xref: /linux/mm/filemap.c (revision af50e4ba34f4c45e92535364133d4deb5931c1c5)
1 /*
2  *	linux/mm/filemap.c
3  *
4  * Copyright (C) 1994-1999  Linus Torvalds
5  */
6 
7 /*
8  * This file handles the generic file mmap semantics used by
9  * most "normal" filesystems (but you don't /have/ to use this:
10  * the NFS filesystem used to do this differently, for example)
11  */
12 #include <linux/export.h>
13 #include <linux/compiler.h>
14 #include <linux/dax.h>
15 #include <linux/fs.h>
16 #include <linux/sched/signal.h>
17 #include <linux/uaccess.h>
18 #include <linux/capability.h>
19 #include <linux/kernel_stat.h>
20 #include <linux/gfp.h>
21 #include <linux/mm.h>
22 #include <linux/swap.h>
23 #include <linux/mman.h>
24 #include <linux/pagemap.h>
25 #include <linux/file.h>
26 #include <linux/uio.h>
27 #include <linux/hash.h>
28 #include <linux/writeback.h>
29 #include <linux/backing-dev.h>
30 #include <linux/pagevec.h>
31 #include <linux/blkdev.h>
32 #include <linux/security.h>
33 #include <linux/cpuset.h>
34 #include <linux/hugetlb.h>
35 #include <linux/memcontrol.h>
36 #include <linux/cleancache.h>
37 #include <linux/shmem_fs.h>
38 #include <linux/rmap.h>
39 #include "internal.h"
40 
41 #define CREATE_TRACE_POINTS
42 #include <trace/events/filemap.h>
43 
44 /*
45  * FIXME: remove all knowledge of the buffer layer from the core VM
46  */
47 #include <linux/buffer_head.h> /* for try_to_free_buffers */
48 
49 #include <asm/mman.h>
50 
51 /*
52  * Shared mappings implemented 30.11.1994. It's not fully working yet,
53  * though.
54  *
55  * Shared mappings now work. 15.8.1995  Bruno.
56  *
57  * finished 'unifying' the page and buffer cache and SMP-threaded the
58  * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
59  *
60  * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
61  */
62 
63 /*
64  * Lock ordering:
65  *
66  *  ->i_mmap_rwsem		(truncate_pagecache)
67  *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
68  *      ->swap_lock		(exclusive_swap_page, others)
69  *        ->i_pages lock
70  *
71  *  ->i_mutex
72  *    ->i_mmap_rwsem		(truncate->unmap_mapping_range)
73  *
74  *  ->mmap_sem
75  *    ->i_mmap_rwsem
76  *      ->page_table_lock or pte_lock	(various, mainly in memory.c)
77  *        ->i_pages lock	(arch-dependent flush_dcache_mmap_lock)
78  *
79  *  ->mmap_sem
80  *    ->lock_page		(access_process_vm)
81  *
82  *  ->i_mutex			(generic_perform_write)
83  *    ->mmap_sem		(fault_in_pages_readable->do_page_fault)
84  *
85  *  bdi->wb.list_lock
86  *    sb_lock			(fs/fs-writeback.c)
87  *    ->i_pages lock		(__sync_single_inode)
88  *
89  *  ->i_mmap_rwsem
90  *    ->anon_vma.lock		(vma_adjust)
91  *
92  *  ->anon_vma.lock
93  *    ->page_table_lock or pte_lock	(anon_vma_prepare and various)
94  *
95  *  ->page_table_lock or pte_lock
96  *    ->swap_lock		(try_to_unmap_one)
97  *    ->private_lock		(try_to_unmap_one)
98  *    ->i_pages lock		(try_to_unmap_one)
99  *    ->zone_lru_lock(zone)	(follow_page->mark_page_accessed)
100  *    ->zone_lru_lock(zone)	(check_pte_range->isolate_lru_page)
101  *    ->private_lock		(page_remove_rmap->set_page_dirty)
102  *    ->i_pages lock		(page_remove_rmap->set_page_dirty)
103  *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
104  *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
105  *    ->memcg->move_lock	(page_remove_rmap->lock_page_memcg)
106  *    bdi.wb->list_lock		(zap_pte_range->set_page_dirty)
107  *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
108  *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
109  *
110  * ->i_mmap_rwsem
111  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
112  */
113 
114 static int page_cache_tree_insert(struct address_space *mapping,
115 				  struct page *page, void **shadowp)
116 {
117 	struct radix_tree_node *node;
118 	void **slot;
119 	int error;
120 
121 	error = __radix_tree_create(&mapping->i_pages, page->index, 0,
122 				    &node, &slot);
123 	if (error)
124 		return error;
125 	if (*slot) {
126 		void *p;
127 
128 		p = radix_tree_deref_slot_protected(slot,
129 						    &mapping->i_pages.xa_lock);
130 		if (!radix_tree_exceptional_entry(p))
131 			return -EEXIST;
132 
133 		mapping->nrexceptional--;
134 		if (shadowp)
135 			*shadowp = p;
136 	}
137 	__radix_tree_replace(&mapping->i_pages, node, slot, page,
138 			     workingset_lookup_update(mapping));
139 	mapping->nrpages++;
140 	return 0;
141 }
142 
143 static void page_cache_tree_delete(struct address_space *mapping,
144 				   struct page *page, void *shadow)
145 {
146 	int i, nr;
147 
148 	/* hugetlb pages are represented by one entry in the radix tree */
149 	nr = PageHuge(page) ? 1 : hpage_nr_pages(page);
150 
151 	VM_BUG_ON_PAGE(!PageLocked(page), page);
152 	VM_BUG_ON_PAGE(PageTail(page), page);
153 	VM_BUG_ON_PAGE(nr != 1 && shadow, page);
154 
155 	for (i = 0; i < nr; i++) {
156 		struct radix_tree_node *node;
157 		void **slot;
158 
159 		__radix_tree_lookup(&mapping->i_pages, page->index + i,
160 				    &node, &slot);
161 
162 		VM_BUG_ON_PAGE(!node && nr != 1, page);
163 
164 		radix_tree_clear_tags(&mapping->i_pages, node, slot);
165 		__radix_tree_replace(&mapping->i_pages, node, slot, shadow,
166 				workingset_lookup_update(mapping));
167 	}
168 
169 	page->mapping = NULL;
170 	/* Leave page->index set: truncation lookup relies upon it */
171 
172 	if (shadow) {
173 		mapping->nrexceptional += nr;
174 		/*
175 		 * Make sure the nrexceptional update is committed before
176 		 * the nrpages update so that final truncate racing
177 		 * with reclaim does not see both counters 0 at the
178 		 * same time and miss a shadow entry.
179 		 */
180 		smp_wmb();
181 	}
182 	mapping->nrpages -= nr;
183 }
184 
185 static void unaccount_page_cache_page(struct address_space *mapping,
186 				      struct page *page)
187 {
188 	int nr;
189 
190 	/*
191 	 * if we're uptodate, flush out into the cleancache, otherwise
192 	 * invalidate any existing cleancache entries.  We can't leave
193 	 * stale data around in the cleancache once our page is gone
194 	 */
195 	if (PageUptodate(page) && PageMappedToDisk(page))
196 		cleancache_put_page(page);
197 	else
198 		cleancache_invalidate_page(mapping, page);
199 
200 	VM_BUG_ON_PAGE(PageTail(page), page);
201 	VM_BUG_ON_PAGE(page_mapped(page), page);
202 	if (!IS_ENABLED(CONFIG_DEBUG_VM) && unlikely(page_mapped(page))) {
203 		int mapcount;
204 
205 		pr_alert("BUG: Bad page cache in process %s  pfn:%05lx\n",
206 			 current->comm, page_to_pfn(page));
207 		dump_page(page, "still mapped when deleted");
208 		dump_stack();
209 		add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
210 
211 		mapcount = page_mapcount(page);
212 		if (mapping_exiting(mapping) &&
213 		    page_count(page) >= mapcount + 2) {
214 			/*
215 			 * All vmas have already been torn down, so it's
216 			 * a good bet that actually the page is unmapped,
217 			 * and we'd prefer not to leak it: if we're wrong,
218 			 * some other bad page check should catch it later.
219 			 */
220 			page_mapcount_reset(page);
221 			page_ref_sub(page, mapcount);
222 		}
223 	}
224 
225 	/* hugetlb pages do not participate in page cache accounting. */
226 	if (PageHuge(page))
227 		return;
228 
229 	nr = hpage_nr_pages(page);
230 
231 	__mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, -nr);
232 	if (PageSwapBacked(page)) {
233 		__mod_node_page_state(page_pgdat(page), NR_SHMEM, -nr);
234 		if (PageTransHuge(page))
235 			__dec_node_page_state(page, NR_SHMEM_THPS);
236 	} else {
237 		VM_BUG_ON_PAGE(PageTransHuge(page), page);
238 	}
239 
240 	/*
241 	 * At this point page must be either written or cleaned by
242 	 * truncate.  Dirty page here signals a bug and loss of
243 	 * unwritten data.
244 	 *
245 	 * This fixes dirty accounting after removing the page entirely
246 	 * but leaves PageDirty set: it has no effect for truncated
247 	 * page and anyway will be cleared before returning page into
248 	 * buddy allocator.
249 	 */
250 	if (WARN_ON_ONCE(PageDirty(page)))
251 		account_page_cleaned(page, mapping, inode_to_wb(mapping->host));
252 }
253 
254 /*
255  * Delete a page from the page cache and free it. Caller has to make
256  * sure the page is locked and that nobody else uses it - or that usage
257  * is safe.  The caller must hold the i_pages lock.
258  */
259 void __delete_from_page_cache(struct page *page, void *shadow)
260 {
261 	struct address_space *mapping = page->mapping;
262 
263 	trace_mm_filemap_delete_from_page_cache(page);
264 
265 	unaccount_page_cache_page(mapping, page);
266 	page_cache_tree_delete(mapping, page, shadow);
267 }
268 
269 static void page_cache_free_page(struct address_space *mapping,
270 				struct page *page)
271 {
272 	void (*freepage)(struct page *);
273 
274 	freepage = mapping->a_ops->freepage;
275 	if (freepage)
276 		freepage(page);
277 
278 	if (PageTransHuge(page) && !PageHuge(page)) {
279 		page_ref_sub(page, HPAGE_PMD_NR);
280 		VM_BUG_ON_PAGE(page_count(page) <= 0, page);
281 	} else {
282 		put_page(page);
283 	}
284 }
285 
286 /**
287  * delete_from_page_cache - delete page from page cache
288  * @page: the page which the kernel is trying to remove from page cache
289  *
290  * This must be called only on pages that have been verified to be in the page
291  * cache and locked.  It will never put the page into the free list, the caller
292  * has a reference on the page.
293  */
294 void delete_from_page_cache(struct page *page)
295 {
296 	struct address_space *mapping = page_mapping(page);
297 	unsigned long flags;
298 
299 	BUG_ON(!PageLocked(page));
300 	xa_lock_irqsave(&mapping->i_pages, flags);
301 	__delete_from_page_cache(page, NULL);
302 	xa_unlock_irqrestore(&mapping->i_pages, flags);
303 
304 	page_cache_free_page(mapping, page);
305 }
306 EXPORT_SYMBOL(delete_from_page_cache);
307 
308 /*
309  * page_cache_tree_delete_batch - delete several pages from page cache
310  * @mapping: the mapping to which pages belong
311  * @pvec: pagevec with pages to delete
312  *
313  * The function walks over mapping->i_pages and removes pages passed in @pvec
314  * from the mapping. The function expects @pvec to be sorted by page index.
315  * It tolerates holes in @pvec (mapping entries at those indices are not
316  * modified). The function expects only THP head pages to be present in the
317  * @pvec and takes care to delete all corresponding tail pages from the
318  * mapping as well.
319  *
320  * The function expects the i_pages lock to be held.
321  */
322 static void
323 page_cache_tree_delete_batch(struct address_space *mapping,
324 			     struct pagevec *pvec)
325 {
326 	struct radix_tree_iter iter;
327 	void **slot;
328 	int total_pages = 0;
329 	int i = 0, tail_pages = 0;
330 	struct page *page;
331 	pgoff_t start;
332 
333 	start = pvec->pages[0]->index;
334 	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
335 		if (i >= pagevec_count(pvec) && !tail_pages)
336 			break;
337 		page = radix_tree_deref_slot_protected(slot,
338 						       &mapping->i_pages.xa_lock);
339 		if (radix_tree_exceptional_entry(page))
340 			continue;
341 		if (!tail_pages) {
342 			/*
343 			 * Some page got inserted in our range? Skip it. We
344 			 * have our pages locked so they are protected from
345 			 * being removed.
346 			 */
347 			if (page != pvec->pages[i])
348 				continue;
349 			WARN_ON_ONCE(!PageLocked(page));
350 			if (PageTransHuge(page) && !PageHuge(page))
351 				tail_pages = HPAGE_PMD_NR - 1;
352 			page->mapping = NULL;
353 			/*
354 			 * Leave page->index set: truncation lookup relies
355 			 * upon it
356 			 */
357 			i++;
358 		} else {
359 			tail_pages--;
360 		}
361 		radix_tree_clear_tags(&mapping->i_pages, iter.node, slot);
362 		__radix_tree_replace(&mapping->i_pages, iter.node, slot, NULL,
363 				workingset_lookup_update(mapping));
364 		total_pages++;
365 	}
366 	mapping->nrpages -= total_pages;
367 }
368 
369 void delete_from_page_cache_batch(struct address_space *mapping,
370 				  struct pagevec *pvec)
371 {
372 	int i;
373 	unsigned long flags;
374 
375 	if (!pagevec_count(pvec))
376 		return;
377 
378 	xa_lock_irqsave(&mapping->i_pages, flags);
379 	for (i = 0; i < pagevec_count(pvec); i++) {
380 		trace_mm_filemap_delete_from_page_cache(pvec->pages[i]);
381 
382 		unaccount_page_cache_page(mapping, pvec->pages[i]);
383 	}
384 	page_cache_tree_delete_batch(mapping, pvec);
385 	xa_unlock_irqrestore(&mapping->i_pages, flags);
386 
387 	for (i = 0; i < pagevec_count(pvec); i++)
388 		page_cache_free_page(mapping, pvec->pages[i]);
389 }
390 
391 int filemap_check_errors(struct address_space *mapping)
392 {
393 	int ret = 0;
394 	/* Check for outstanding write errors */
395 	if (test_bit(AS_ENOSPC, &mapping->flags) &&
396 	    test_and_clear_bit(AS_ENOSPC, &mapping->flags))
397 		ret = -ENOSPC;
398 	if (test_bit(AS_EIO, &mapping->flags) &&
399 	    test_and_clear_bit(AS_EIO, &mapping->flags))
400 		ret = -EIO;
401 	return ret;
402 }
403 EXPORT_SYMBOL(filemap_check_errors);
404 
405 static int filemap_check_and_keep_errors(struct address_space *mapping)
406 {
407 	/* Check for outstanding write errors */
408 	if (test_bit(AS_EIO, &mapping->flags))
409 		return -EIO;
410 	if (test_bit(AS_ENOSPC, &mapping->flags))
411 		return -ENOSPC;
412 	return 0;
413 }
414 
415 /**
416  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
417  * @mapping:	address space structure to write
418  * @start:	offset in bytes where the range starts
419  * @end:	offset in bytes where the range ends (inclusive)
420  * @sync_mode:	enable synchronous operation
421  *
422  * Start writeback against all of a mapping's dirty pages that lie
423  * within the byte offsets <start, end> inclusive.
424  *
425  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
426  * opposed to a regular memory cleansing writeback.  The difference between
427  * these two operations is that if a dirty page/buffer is encountered, it must
428  * be waited upon, and not just skipped over.
429  */
430 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
431 				loff_t end, int sync_mode)
432 {
433 	int ret;
434 	struct writeback_control wbc = {
435 		.sync_mode = sync_mode,
436 		.nr_to_write = LONG_MAX,
437 		.range_start = start,
438 		.range_end = end,
439 	};
440 
441 	if (!mapping_cap_writeback_dirty(mapping))
442 		return 0;
443 
444 	wbc_attach_fdatawrite_inode(&wbc, mapping->host);
445 	ret = do_writepages(mapping, &wbc);
446 	wbc_detach_inode(&wbc);
447 	return ret;
448 }
449 
450 static inline int __filemap_fdatawrite(struct address_space *mapping,
451 	int sync_mode)
452 {
453 	return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
454 }
455 
456 int filemap_fdatawrite(struct address_space *mapping)
457 {
458 	return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
459 }
460 EXPORT_SYMBOL(filemap_fdatawrite);
461 
462 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
463 				loff_t end)
464 {
465 	return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
466 }
467 EXPORT_SYMBOL(filemap_fdatawrite_range);
468 
469 /**
470  * filemap_flush - mostly a non-blocking flush
471  * @mapping:	target address_space
472  *
473  * This is a mostly non-blocking flush.  Not suitable for data-integrity
474  * purposes - I/O may not be started against all dirty pages.
475  */
476 int filemap_flush(struct address_space *mapping)
477 {
478 	return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
479 }
480 EXPORT_SYMBOL(filemap_flush);
481 
482 /**
483  * filemap_range_has_page - check if a page exists in range.
484  * @mapping:           address space within which to check
485  * @start_byte:        offset in bytes where the range starts
486  * @end_byte:          offset in bytes where the range ends (inclusive)
487  *
488  * Find at least one page in the range supplied, usually used to check if
489  * direct writing in this range will trigger a writeback.
490  */
491 bool filemap_range_has_page(struct address_space *mapping,
492 			   loff_t start_byte, loff_t end_byte)
493 {
494 	pgoff_t index = start_byte >> PAGE_SHIFT;
495 	pgoff_t end = end_byte >> PAGE_SHIFT;
496 	struct page *page;
497 
498 	if (end_byte < start_byte)
499 		return false;
500 
501 	if (mapping->nrpages == 0)
502 		return false;
503 
504 	if (!find_get_pages_range(mapping, &index, end, 1, &page))
505 		return false;
506 	put_page(page);
507 	return true;
508 }
509 EXPORT_SYMBOL(filemap_range_has_page);
510 
511 static void __filemap_fdatawait_range(struct address_space *mapping,
512 				     loff_t start_byte, loff_t end_byte)
513 {
514 	pgoff_t index = start_byte >> PAGE_SHIFT;
515 	pgoff_t end = end_byte >> PAGE_SHIFT;
516 	struct pagevec pvec;
517 	int nr_pages;
518 
519 	if (end_byte < start_byte)
520 		return;
521 
522 	pagevec_init(&pvec);
523 	while (index <= end) {
524 		unsigned i;
525 
526 		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
527 				end, PAGECACHE_TAG_WRITEBACK);
528 		if (!nr_pages)
529 			break;
530 
531 		for (i = 0; i < nr_pages; i++) {
532 			struct page *page = pvec.pages[i];
533 
534 			wait_on_page_writeback(page);
535 			ClearPageError(page);
536 		}
537 		pagevec_release(&pvec);
538 		cond_resched();
539 	}
540 }
541 
542 /**
543  * filemap_fdatawait_range - wait for writeback to complete
544  * @mapping:		address space structure to wait for
545  * @start_byte:		offset in bytes where the range starts
546  * @end_byte:		offset in bytes where the range ends (inclusive)
547  *
548  * Walk the list of under-writeback pages of the given address space
549  * in the given range and wait for all of them.  Check error status of
550  * the address space and return it.
551  *
552  * Since the error status of the address space is cleared by this function,
553  * callers are responsible for checking the return value and handling and/or
554  * reporting the error.
555  */
556 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
557 			    loff_t end_byte)
558 {
559 	__filemap_fdatawait_range(mapping, start_byte, end_byte);
560 	return filemap_check_errors(mapping);
561 }
562 EXPORT_SYMBOL(filemap_fdatawait_range);
563 
564 /**
565  * file_fdatawait_range - wait for writeback to complete
566  * @file:		file pointing to address space structure to wait for
567  * @start_byte:		offset in bytes where the range starts
568  * @end_byte:		offset in bytes where the range ends (inclusive)
569  *
570  * Walk the list of under-writeback pages of the address space that file
571  * refers to, in the given range and wait for all of them.  Check error
572  * status of the address space vs. the file->f_wb_err cursor and return it.
573  *
574  * Since the error status of the file is advanced by this function,
575  * callers are responsible for checking the return value and handling and/or
576  * reporting the error.
577  */
578 int file_fdatawait_range(struct file *file, loff_t start_byte, loff_t end_byte)
579 {
580 	struct address_space *mapping = file->f_mapping;
581 
582 	__filemap_fdatawait_range(mapping, start_byte, end_byte);
583 	return file_check_and_advance_wb_err(file);
584 }
585 EXPORT_SYMBOL(file_fdatawait_range);
586 
587 /**
588  * filemap_fdatawait_keep_errors - wait for writeback without clearing errors
589  * @mapping: address space structure to wait for
590  *
591  * Walk the list of under-writeback pages of the given address space
592  * and wait for all of them.  Unlike filemap_fdatawait(), this function
593  * does not clear error status of the address space.
594  *
595  * Use this function if callers don't handle errors themselves.  Expected
596  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
597  * fsfreeze(8)
598  */
599 int filemap_fdatawait_keep_errors(struct address_space *mapping)
600 {
601 	__filemap_fdatawait_range(mapping, 0, LLONG_MAX);
602 	return filemap_check_and_keep_errors(mapping);
603 }
604 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
605 
606 static bool mapping_needs_writeback(struct address_space *mapping)
607 {
608 	return (!dax_mapping(mapping) && mapping->nrpages) ||
609 	    (dax_mapping(mapping) && mapping->nrexceptional);
610 }
611 
612 int filemap_write_and_wait(struct address_space *mapping)
613 {
614 	int err = 0;
615 
616 	if (mapping_needs_writeback(mapping)) {
617 		err = filemap_fdatawrite(mapping);
618 		/*
619 		 * Even if the above returned error, the pages may be
620 		 * written partially (e.g. -ENOSPC), so we wait for it.
621 		 * But the -EIO is special case, it may indicate the worst
622 		 * thing (e.g. bug) happened, so we avoid waiting for it.
623 		 */
624 		if (err != -EIO) {
625 			int err2 = filemap_fdatawait(mapping);
626 			if (!err)
627 				err = err2;
628 		} else {
629 			/* Clear any previously stored errors */
630 			filemap_check_errors(mapping);
631 		}
632 	} else {
633 		err = filemap_check_errors(mapping);
634 	}
635 	return err;
636 }
637 EXPORT_SYMBOL(filemap_write_and_wait);
638 
639 /**
640  * filemap_write_and_wait_range - write out & wait on a file range
641  * @mapping:	the address_space for the pages
642  * @lstart:	offset in bytes where the range starts
643  * @lend:	offset in bytes where the range ends (inclusive)
644  *
645  * Write out and wait upon file offsets lstart->lend, inclusive.
646  *
647  * Note that @lend is inclusive (describes the last byte to be written) so
648  * that this function can be used to write to the very end-of-file (end = -1).
649  */
650 int filemap_write_and_wait_range(struct address_space *mapping,
651 				 loff_t lstart, loff_t lend)
652 {
653 	int err = 0;
654 
655 	if (mapping_needs_writeback(mapping)) {
656 		err = __filemap_fdatawrite_range(mapping, lstart, lend,
657 						 WB_SYNC_ALL);
658 		/* See comment of filemap_write_and_wait() */
659 		if (err != -EIO) {
660 			int err2 = filemap_fdatawait_range(mapping,
661 						lstart, lend);
662 			if (!err)
663 				err = err2;
664 		} else {
665 			/* Clear any previously stored errors */
666 			filemap_check_errors(mapping);
667 		}
668 	} else {
669 		err = filemap_check_errors(mapping);
670 	}
671 	return err;
672 }
673 EXPORT_SYMBOL(filemap_write_and_wait_range);
674 
675 void __filemap_set_wb_err(struct address_space *mapping, int err)
676 {
677 	errseq_t eseq = errseq_set(&mapping->wb_err, err);
678 
679 	trace_filemap_set_wb_err(mapping, eseq);
680 }
681 EXPORT_SYMBOL(__filemap_set_wb_err);
682 
683 /**
684  * file_check_and_advance_wb_err - report wb error (if any) that was previously
685  * 				   and advance wb_err to current one
686  * @file: struct file on which the error is being reported
687  *
688  * When userland calls fsync (or something like nfsd does the equivalent), we
689  * want to report any writeback errors that occurred since the last fsync (or
690  * since the file was opened if there haven't been any).
691  *
692  * Grab the wb_err from the mapping. If it matches what we have in the file,
693  * then just quickly return 0. The file is all caught up.
694  *
695  * If it doesn't match, then take the mapping value, set the "seen" flag in
696  * it and try to swap it into place. If it works, or another task beat us
697  * to it with the new value, then update the f_wb_err and return the error
698  * portion. The error at this point must be reported via proper channels
699  * (a'la fsync, or NFS COMMIT operation, etc.).
700  *
701  * While we handle mapping->wb_err with atomic operations, the f_wb_err
702  * value is protected by the f_lock since we must ensure that it reflects
703  * the latest value swapped in for this file descriptor.
704  */
705 int file_check_and_advance_wb_err(struct file *file)
706 {
707 	int err = 0;
708 	errseq_t old = READ_ONCE(file->f_wb_err);
709 	struct address_space *mapping = file->f_mapping;
710 
711 	/* Locklessly handle the common case where nothing has changed */
712 	if (errseq_check(&mapping->wb_err, old)) {
713 		/* Something changed, must use slow path */
714 		spin_lock(&file->f_lock);
715 		old = file->f_wb_err;
716 		err = errseq_check_and_advance(&mapping->wb_err,
717 						&file->f_wb_err);
718 		trace_file_check_and_advance_wb_err(file, old);
719 		spin_unlock(&file->f_lock);
720 	}
721 
722 	/*
723 	 * We're mostly using this function as a drop in replacement for
724 	 * filemap_check_errors. Clear AS_EIO/AS_ENOSPC to emulate the effect
725 	 * that the legacy code would have had on these flags.
726 	 */
727 	clear_bit(AS_EIO, &mapping->flags);
728 	clear_bit(AS_ENOSPC, &mapping->flags);
729 	return err;
730 }
731 EXPORT_SYMBOL(file_check_and_advance_wb_err);
732 
733 /**
734  * file_write_and_wait_range - write out & wait on a file range
735  * @file:	file pointing to address_space with pages
736  * @lstart:	offset in bytes where the range starts
737  * @lend:	offset in bytes where the range ends (inclusive)
738  *
739  * Write out and wait upon file offsets lstart->lend, inclusive.
740  *
741  * Note that @lend is inclusive (describes the last byte to be written) so
742  * that this function can be used to write to the very end-of-file (end = -1).
743  *
744  * After writing out and waiting on the data, we check and advance the
745  * f_wb_err cursor to the latest value, and return any errors detected there.
746  */
747 int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
748 {
749 	int err = 0, err2;
750 	struct address_space *mapping = file->f_mapping;
751 
752 	if (mapping_needs_writeback(mapping)) {
753 		err = __filemap_fdatawrite_range(mapping, lstart, lend,
754 						 WB_SYNC_ALL);
755 		/* See comment of filemap_write_and_wait() */
756 		if (err != -EIO)
757 			__filemap_fdatawait_range(mapping, lstart, lend);
758 	}
759 	err2 = file_check_and_advance_wb_err(file);
760 	if (!err)
761 		err = err2;
762 	return err;
763 }
764 EXPORT_SYMBOL(file_write_and_wait_range);
765 
766 /**
767  * replace_page_cache_page - replace a pagecache page with a new one
768  * @old:	page to be replaced
769  * @new:	page to replace with
770  * @gfp_mask:	allocation mode
771  *
772  * This function replaces a page in the pagecache with a new one.  On
773  * success it acquires the pagecache reference for the new page and
774  * drops it for the old page.  Both the old and new pages must be
775  * locked.  This function does not add the new page to the LRU, the
776  * caller must do that.
777  *
778  * The remove + add is atomic.  The only way this function can fail is
779  * memory allocation failure.
780  */
781 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
782 {
783 	int error;
784 
785 	VM_BUG_ON_PAGE(!PageLocked(old), old);
786 	VM_BUG_ON_PAGE(!PageLocked(new), new);
787 	VM_BUG_ON_PAGE(new->mapping, new);
788 
789 	error = radix_tree_preload(gfp_mask & GFP_RECLAIM_MASK);
790 	if (!error) {
791 		struct address_space *mapping = old->mapping;
792 		void (*freepage)(struct page *);
793 		unsigned long flags;
794 
795 		pgoff_t offset = old->index;
796 		freepage = mapping->a_ops->freepage;
797 
798 		get_page(new);
799 		new->mapping = mapping;
800 		new->index = offset;
801 
802 		xa_lock_irqsave(&mapping->i_pages, flags);
803 		__delete_from_page_cache(old, NULL);
804 		error = page_cache_tree_insert(mapping, new, NULL);
805 		BUG_ON(error);
806 
807 		/*
808 		 * hugetlb pages do not participate in page cache accounting.
809 		 */
810 		if (!PageHuge(new))
811 			__inc_node_page_state(new, NR_FILE_PAGES);
812 		if (PageSwapBacked(new))
813 			__inc_node_page_state(new, NR_SHMEM);
814 		xa_unlock_irqrestore(&mapping->i_pages, flags);
815 		mem_cgroup_migrate(old, new);
816 		radix_tree_preload_end();
817 		if (freepage)
818 			freepage(old);
819 		put_page(old);
820 	}
821 
822 	return error;
823 }
824 EXPORT_SYMBOL_GPL(replace_page_cache_page);
825 
826 static int __add_to_page_cache_locked(struct page *page,
827 				      struct address_space *mapping,
828 				      pgoff_t offset, gfp_t gfp_mask,
829 				      void **shadowp)
830 {
831 	int huge = PageHuge(page);
832 	struct mem_cgroup *memcg;
833 	int error;
834 
835 	VM_BUG_ON_PAGE(!PageLocked(page), page);
836 	VM_BUG_ON_PAGE(PageSwapBacked(page), page);
837 
838 	if (!huge) {
839 		error = mem_cgroup_try_charge(page, current->mm,
840 					      gfp_mask, &memcg, false);
841 		if (error)
842 			return error;
843 	}
844 
845 	error = radix_tree_maybe_preload(gfp_mask & GFP_RECLAIM_MASK);
846 	if (error) {
847 		if (!huge)
848 			mem_cgroup_cancel_charge(page, memcg, false);
849 		return error;
850 	}
851 
852 	get_page(page);
853 	page->mapping = mapping;
854 	page->index = offset;
855 
856 	xa_lock_irq(&mapping->i_pages);
857 	error = page_cache_tree_insert(mapping, page, shadowp);
858 	radix_tree_preload_end();
859 	if (unlikely(error))
860 		goto err_insert;
861 
862 	/* hugetlb pages do not participate in page cache accounting. */
863 	if (!huge)
864 		__inc_node_page_state(page, NR_FILE_PAGES);
865 	xa_unlock_irq(&mapping->i_pages);
866 	if (!huge)
867 		mem_cgroup_commit_charge(page, memcg, false, false);
868 	trace_mm_filemap_add_to_page_cache(page);
869 	return 0;
870 err_insert:
871 	page->mapping = NULL;
872 	/* Leave page->index set: truncation relies upon it */
873 	xa_unlock_irq(&mapping->i_pages);
874 	if (!huge)
875 		mem_cgroup_cancel_charge(page, memcg, false);
876 	put_page(page);
877 	return error;
878 }
879 
880 /**
881  * add_to_page_cache_locked - add a locked page to the pagecache
882  * @page:	page to add
883  * @mapping:	the page's address_space
884  * @offset:	page index
885  * @gfp_mask:	page allocation mode
886  *
887  * This function is used to add a page to the pagecache. It must be locked.
888  * This function does not add the page to the LRU.  The caller must do that.
889  */
890 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
891 		pgoff_t offset, gfp_t gfp_mask)
892 {
893 	return __add_to_page_cache_locked(page, mapping, offset,
894 					  gfp_mask, NULL);
895 }
896 EXPORT_SYMBOL(add_to_page_cache_locked);
897 
898 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
899 				pgoff_t offset, gfp_t gfp_mask)
900 {
901 	void *shadow = NULL;
902 	int ret;
903 
904 	__SetPageLocked(page);
905 	ret = __add_to_page_cache_locked(page, mapping, offset,
906 					 gfp_mask, &shadow);
907 	if (unlikely(ret))
908 		__ClearPageLocked(page);
909 	else {
910 		/*
911 		 * The page might have been evicted from cache only
912 		 * recently, in which case it should be activated like
913 		 * any other repeatedly accessed page.
914 		 * The exception is pages getting rewritten; evicting other
915 		 * data from the working set, only to cache data that will
916 		 * get overwritten with something else, is a waste of memory.
917 		 */
918 		if (!(gfp_mask & __GFP_WRITE) &&
919 		    shadow && workingset_refault(shadow)) {
920 			SetPageActive(page);
921 			workingset_activation(page);
922 		} else
923 			ClearPageActive(page);
924 		lru_cache_add(page);
925 	}
926 	return ret;
927 }
928 EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
929 
930 #ifdef CONFIG_NUMA
931 struct page *__page_cache_alloc(gfp_t gfp)
932 {
933 	int n;
934 	struct page *page;
935 
936 	if (cpuset_do_page_mem_spread()) {
937 		unsigned int cpuset_mems_cookie;
938 		do {
939 			cpuset_mems_cookie = read_mems_allowed_begin();
940 			n = cpuset_mem_spread_node();
941 			page = __alloc_pages_node(n, gfp, 0);
942 		} while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
943 
944 		return page;
945 	}
946 	return alloc_pages(gfp, 0);
947 }
948 EXPORT_SYMBOL(__page_cache_alloc);
949 #endif
950 
951 /*
952  * In order to wait for pages to become available there must be
953  * waitqueues associated with pages. By using a hash table of
954  * waitqueues where the bucket discipline is to maintain all
955  * waiters on the same queue and wake all when any of the pages
956  * become available, and for the woken contexts to check to be
957  * sure the appropriate page became available, this saves space
958  * at a cost of "thundering herd" phenomena during rare hash
959  * collisions.
960  */
961 #define PAGE_WAIT_TABLE_BITS 8
962 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
963 static wait_queue_head_t page_wait_table[PAGE_WAIT_TABLE_SIZE] __cacheline_aligned;
964 
965 static wait_queue_head_t *page_waitqueue(struct page *page)
966 {
967 	return &page_wait_table[hash_ptr(page, PAGE_WAIT_TABLE_BITS)];
968 }
969 
970 void __init pagecache_init(void)
971 {
972 	int i;
973 
974 	for (i = 0; i < PAGE_WAIT_TABLE_SIZE; i++)
975 		init_waitqueue_head(&page_wait_table[i]);
976 
977 	page_writeback_init();
978 }
979 
980 /* This has the same layout as wait_bit_key - see fs/cachefiles/rdwr.c */
981 struct wait_page_key {
982 	struct page *page;
983 	int bit_nr;
984 	int page_match;
985 };
986 
987 struct wait_page_queue {
988 	struct page *page;
989 	int bit_nr;
990 	wait_queue_entry_t wait;
991 };
992 
993 static int wake_page_function(wait_queue_entry_t *wait, unsigned mode, int sync, void *arg)
994 {
995 	struct wait_page_key *key = arg;
996 	struct wait_page_queue *wait_page
997 		= container_of(wait, struct wait_page_queue, wait);
998 
999 	if (wait_page->page != key->page)
1000 	       return 0;
1001 	key->page_match = 1;
1002 
1003 	if (wait_page->bit_nr != key->bit_nr)
1004 		return 0;
1005 
1006 	/* Stop walking if it's locked */
1007 	if (test_bit(key->bit_nr, &key->page->flags))
1008 		return -1;
1009 
1010 	return autoremove_wake_function(wait, mode, sync, key);
1011 }
1012 
1013 static void wake_up_page_bit(struct page *page, int bit_nr)
1014 {
1015 	wait_queue_head_t *q = page_waitqueue(page);
1016 	struct wait_page_key key;
1017 	unsigned long flags;
1018 	wait_queue_entry_t bookmark;
1019 
1020 	key.page = page;
1021 	key.bit_nr = bit_nr;
1022 	key.page_match = 0;
1023 
1024 	bookmark.flags = 0;
1025 	bookmark.private = NULL;
1026 	bookmark.func = NULL;
1027 	INIT_LIST_HEAD(&bookmark.entry);
1028 
1029 	spin_lock_irqsave(&q->lock, flags);
1030 	__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
1031 
1032 	while (bookmark.flags & WQ_FLAG_BOOKMARK) {
1033 		/*
1034 		 * Take a breather from holding the lock,
1035 		 * allow pages that finish wake up asynchronously
1036 		 * to acquire the lock and remove themselves
1037 		 * from wait queue
1038 		 */
1039 		spin_unlock_irqrestore(&q->lock, flags);
1040 		cpu_relax();
1041 		spin_lock_irqsave(&q->lock, flags);
1042 		__wake_up_locked_key_bookmark(q, TASK_NORMAL, &key, &bookmark);
1043 	}
1044 
1045 	/*
1046 	 * It is possible for other pages to have collided on the waitqueue
1047 	 * hash, so in that case check for a page match. That prevents a long-
1048 	 * term waiter
1049 	 *
1050 	 * It is still possible to miss a case here, when we woke page waiters
1051 	 * and removed them from the waitqueue, but there are still other
1052 	 * page waiters.
1053 	 */
1054 	if (!waitqueue_active(q) || !key.page_match) {
1055 		ClearPageWaiters(page);
1056 		/*
1057 		 * It's possible to miss clearing Waiters here, when we woke
1058 		 * our page waiters, but the hashed waitqueue has waiters for
1059 		 * other pages on it.
1060 		 *
1061 		 * That's okay, it's a rare case. The next waker will clear it.
1062 		 */
1063 	}
1064 	spin_unlock_irqrestore(&q->lock, flags);
1065 }
1066 
1067 static void wake_up_page(struct page *page, int bit)
1068 {
1069 	if (!PageWaiters(page))
1070 		return;
1071 	wake_up_page_bit(page, bit);
1072 }
1073 
1074 static inline int wait_on_page_bit_common(wait_queue_head_t *q,
1075 		struct page *page, int bit_nr, int state, bool lock)
1076 {
1077 	struct wait_page_queue wait_page;
1078 	wait_queue_entry_t *wait = &wait_page.wait;
1079 	int ret = 0;
1080 
1081 	init_wait(wait);
1082 	wait->flags = lock ? WQ_FLAG_EXCLUSIVE : 0;
1083 	wait->func = wake_page_function;
1084 	wait_page.page = page;
1085 	wait_page.bit_nr = bit_nr;
1086 
1087 	for (;;) {
1088 		spin_lock_irq(&q->lock);
1089 
1090 		if (likely(list_empty(&wait->entry))) {
1091 			__add_wait_queue_entry_tail(q, wait);
1092 			SetPageWaiters(page);
1093 		}
1094 
1095 		set_current_state(state);
1096 
1097 		spin_unlock_irq(&q->lock);
1098 
1099 		if (likely(test_bit(bit_nr, &page->flags))) {
1100 			io_schedule();
1101 		}
1102 
1103 		if (lock) {
1104 			if (!test_and_set_bit_lock(bit_nr, &page->flags))
1105 				break;
1106 		} else {
1107 			if (!test_bit(bit_nr, &page->flags))
1108 				break;
1109 		}
1110 
1111 		if (unlikely(signal_pending_state(state, current))) {
1112 			ret = -EINTR;
1113 			break;
1114 		}
1115 	}
1116 
1117 	finish_wait(q, wait);
1118 
1119 	/*
1120 	 * A signal could leave PageWaiters set. Clearing it here if
1121 	 * !waitqueue_active would be possible (by open-coding finish_wait),
1122 	 * but still fail to catch it in the case of wait hash collision. We
1123 	 * already can fail to clear wait hash collision cases, so don't
1124 	 * bother with signals either.
1125 	 */
1126 
1127 	return ret;
1128 }
1129 
1130 void wait_on_page_bit(struct page *page, int bit_nr)
1131 {
1132 	wait_queue_head_t *q = page_waitqueue(page);
1133 	wait_on_page_bit_common(q, page, bit_nr, TASK_UNINTERRUPTIBLE, false);
1134 }
1135 EXPORT_SYMBOL(wait_on_page_bit);
1136 
1137 int wait_on_page_bit_killable(struct page *page, int bit_nr)
1138 {
1139 	wait_queue_head_t *q = page_waitqueue(page);
1140 	return wait_on_page_bit_common(q, page, bit_nr, TASK_KILLABLE, false);
1141 }
1142 EXPORT_SYMBOL(wait_on_page_bit_killable);
1143 
1144 /**
1145  * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
1146  * @page: Page defining the wait queue of interest
1147  * @waiter: Waiter to add to the queue
1148  *
1149  * Add an arbitrary @waiter to the wait queue for the nominated @page.
1150  */
1151 void add_page_wait_queue(struct page *page, wait_queue_entry_t *waiter)
1152 {
1153 	wait_queue_head_t *q = page_waitqueue(page);
1154 	unsigned long flags;
1155 
1156 	spin_lock_irqsave(&q->lock, flags);
1157 	__add_wait_queue_entry_tail(q, waiter);
1158 	SetPageWaiters(page);
1159 	spin_unlock_irqrestore(&q->lock, flags);
1160 }
1161 EXPORT_SYMBOL_GPL(add_page_wait_queue);
1162 
1163 #ifndef clear_bit_unlock_is_negative_byte
1164 
1165 /*
1166  * PG_waiters is the high bit in the same byte as PG_lock.
1167  *
1168  * On x86 (and on many other architectures), we can clear PG_lock and
1169  * test the sign bit at the same time. But if the architecture does
1170  * not support that special operation, we just do this all by hand
1171  * instead.
1172  *
1173  * The read of PG_waiters has to be after (or concurrently with) PG_locked
1174  * being cleared, but a memory barrier should be unneccssary since it is
1175  * in the same byte as PG_locked.
1176  */
1177 static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
1178 {
1179 	clear_bit_unlock(nr, mem);
1180 	/* smp_mb__after_atomic(); */
1181 	return test_bit(PG_waiters, mem);
1182 }
1183 
1184 #endif
1185 
1186 /**
1187  * unlock_page - unlock a locked page
1188  * @page: the page
1189  *
1190  * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
1191  * Also wakes sleepers in wait_on_page_writeback() because the wakeup
1192  * mechanism between PageLocked pages and PageWriteback pages is shared.
1193  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
1194  *
1195  * Note that this depends on PG_waiters being the sign bit in the byte
1196  * that contains PG_locked - thus the BUILD_BUG_ON(). That allows us to
1197  * clear the PG_locked bit and test PG_waiters at the same time fairly
1198  * portably (architectures that do LL/SC can test any bit, while x86 can
1199  * test the sign bit).
1200  */
1201 void unlock_page(struct page *page)
1202 {
1203 	BUILD_BUG_ON(PG_waiters != 7);
1204 	page = compound_head(page);
1205 	VM_BUG_ON_PAGE(!PageLocked(page), page);
1206 	if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
1207 		wake_up_page_bit(page, PG_locked);
1208 }
1209 EXPORT_SYMBOL(unlock_page);
1210 
1211 /**
1212  * end_page_writeback - end writeback against a page
1213  * @page: the page
1214  */
1215 void end_page_writeback(struct page *page)
1216 {
1217 	/*
1218 	 * TestClearPageReclaim could be used here but it is an atomic
1219 	 * operation and overkill in this particular case. Failing to
1220 	 * shuffle a page marked for immediate reclaim is too mild to
1221 	 * justify taking an atomic operation penalty at the end of
1222 	 * ever page writeback.
1223 	 */
1224 	if (PageReclaim(page)) {
1225 		ClearPageReclaim(page);
1226 		rotate_reclaimable_page(page);
1227 	}
1228 
1229 	if (!test_clear_page_writeback(page))
1230 		BUG();
1231 
1232 	smp_mb__after_atomic();
1233 	wake_up_page(page, PG_writeback);
1234 }
1235 EXPORT_SYMBOL(end_page_writeback);
1236 
1237 /*
1238  * After completing I/O on a page, call this routine to update the page
1239  * flags appropriately
1240  */
1241 void page_endio(struct page *page, bool is_write, int err)
1242 {
1243 	if (!is_write) {
1244 		if (!err) {
1245 			SetPageUptodate(page);
1246 		} else {
1247 			ClearPageUptodate(page);
1248 			SetPageError(page);
1249 		}
1250 		unlock_page(page);
1251 	} else {
1252 		if (err) {
1253 			struct address_space *mapping;
1254 
1255 			SetPageError(page);
1256 			mapping = page_mapping(page);
1257 			if (mapping)
1258 				mapping_set_error(mapping, err);
1259 		}
1260 		end_page_writeback(page);
1261 	}
1262 }
1263 EXPORT_SYMBOL_GPL(page_endio);
1264 
1265 /**
1266  * __lock_page - get a lock on the page, assuming we need to sleep to get it
1267  * @__page: the page to lock
1268  */
1269 void __lock_page(struct page *__page)
1270 {
1271 	struct page *page = compound_head(__page);
1272 	wait_queue_head_t *q = page_waitqueue(page);
1273 	wait_on_page_bit_common(q, page, PG_locked, TASK_UNINTERRUPTIBLE, true);
1274 }
1275 EXPORT_SYMBOL(__lock_page);
1276 
1277 int __lock_page_killable(struct page *__page)
1278 {
1279 	struct page *page = compound_head(__page);
1280 	wait_queue_head_t *q = page_waitqueue(page);
1281 	return wait_on_page_bit_common(q, page, PG_locked, TASK_KILLABLE, true);
1282 }
1283 EXPORT_SYMBOL_GPL(__lock_page_killable);
1284 
1285 /*
1286  * Return values:
1287  * 1 - page is locked; mmap_sem is still held.
1288  * 0 - page is not locked.
1289  *     mmap_sem has been released (up_read()), unless flags had both
1290  *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
1291  *     which case mmap_sem is still held.
1292  *
1293  * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
1294  * with the page locked and the mmap_sem unperturbed.
1295  */
1296 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
1297 			 unsigned int flags)
1298 {
1299 	if (flags & FAULT_FLAG_ALLOW_RETRY) {
1300 		/*
1301 		 * CAUTION! In this case, mmap_sem is not released
1302 		 * even though return 0.
1303 		 */
1304 		if (flags & FAULT_FLAG_RETRY_NOWAIT)
1305 			return 0;
1306 
1307 		up_read(&mm->mmap_sem);
1308 		if (flags & FAULT_FLAG_KILLABLE)
1309 			wait_on_page_locked_killable(page);
1310 		else
1311 			wait_on_page_locked(page);
1312 		return 0;
1313 	} else {
1314 		if (flags & FAULT_FLAG_KILLABLE) {
1315 			int ret;
1316 
1317 			ret = __lock_page_killable(page);
1318 			if (ret) {
1319 				up_read(&mm->mmap_sem);
1320 				return 0;
1321 			}
1322 		} else
1323 			__lock_page(page);
1324 		return 1;
1325 	}
1326 }
1327 
1328 /**
1329  * page_cache_next_hole - find the next hole (not-present entry)
1330  * @mapping: mapping
1331  * @index: index
1332  * @max_scan: maximum range to search
1333  *
1334  * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the
1335  * lowest indexed hole.
1336  *
1337  * Returns: the index of the hole if found, otherwise returns an index
1338  * outside of the set specified (in which case 'return - index >=
1339  * max_scan' will be true). In rare cases of index wrap-around, 0 will
1340  * be returned.
1341  *
1342  * page_cache_next_hole may be called under rcu_read_lock. However,
1343  * like radix_tree_gang_lookup, this will not atomically search a
1344  * snapshot of the tree at a single point in time. For example, if a
1345  * hole is created at index 5, then subsequently a hole is created at
1346  * index 10, page_cache_next_hole covering both indexes may return 10
1347  * if called under rcu_read_lock.
1348  */
1349 pgoff_t page_cache_next_hole(struct address_space *mapping,
1350 			     pgoff_t index, unsigned long max_scan)
1351 {
1352 	unsigned long i;
1353 
1354 	for (i = 0; i < max_scan; i++) {
1355 		struct page *page;
1356 
1357 		page = radix_tree_lookup(&mapping->i_pages, index);
1358 		if (!page || radix_tree_exceptional_entry(page))
1359 			break;
1360 		index++;
1361 		if (index == 0)
1362 			break;
1363 	}
1364 
1365 	return index;
1366 }
1367 EXPORT_SYMBOL(page_cache_next_hole);
1368 
1369 /**
1370  * page_cache_prev_hole - find the prev hole (not-present entry)
1371  * @mapping: mapping
1372  * @index: index
1373  * @max_scan: maximum range to search
1374  *
1375  * Search backwards in the range [max(index-max_scan+1, 0), index] for
1376  * the first hole.
1377  *
1378  * Returns: the index of the hole if found, otherwise returns an index
1379  * outside of the set specified (in which case 'index - return >=
1380  * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX
1381  * will be returned.
1382  *
1383  * page_cache_prev_hole may be called under rcu_read_lock. However,
1384  * like radix_tree_gang_lookup, this will not atomically search a
1385  * snapshot of the tree at a single point in time. For example, if a
1386  * hole is created at index 10, then subsequently a hole is created at
1387  * index 5, page_cache_prev_hole covering both indexes may return 5 if
1388  * called under rcu_read_lock.
1389  */
1390 pgoff_t page_cache_prev_hole(struct address_space *mapping,
1391 			     pgoff_t index, unsigned long max_scan)
1392 {
1393 	unsigned long i;
1394 
1395 	for (i = 0; i < max_scan; i++) {
1396 		struct page *page;
1397 
1398 		page = radix_tree_lookup(&mapping->i_pages, index);
1399 		if (!page || radix_tree_exceptional_entry(page))
1400 			break;
1401 		index--;
1402 		if (index == ULONG_MAX)
1403 			break;
1404 	}
1405 
1406 	return index;
1407 }
1408 EXPORT_SYMBOL(page_cache_prev_hole);
1409 
1410 /**
1411  * find_get_entry - find and get a page cache entry
1412  * @mapping: the address_space to search
1413  * @offset: the page cache index
1414  *
1415  * Looks up the page cache slot at @mapping & @offset.  If there is a
1416  * page cache page, it is returned with an increased refcount.
1417  *
1418  * If the slot holds a shadow entry of a previously evicted page, or a
1419  * swap entry from shmem/tmpfs, it is returned.
1420  *
1421  * Otherwise, %NULL is returned.
1422  */
1423 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
1424 {
1425 	void **pagep;
1426 	struct page *head, *page;
1427 
1428 	rcu_read_lock();
1429 repeat:
1430 	page = NULL;
1431 	pagep = radix_tree_lookup_slot(&mapping->i_pages, offset);
1432 	if (pagep) {
1433 		page = radix_tree_deref_slot(pagep);
1434 		if (unlikely(!page))
1435 			goto out;
1436 		if (radix_tree_exception(page)) {
1437 			if (radix_tree_deref_retry(page))
1438 				goto repeat;
1439 			/*
1440 			 * A shadow entry of a recently evicted page,
1441 			 * or a swap entry from shmem/tmpfs.  Return
1442 			 * it without attempting to raise page count.
1443 			 */
1444 			goto out;
1445 		}
1446 
1447 		head = compound_head(page);
1448 		if (!page_cache_get_speculative(head))
1449 			goto repeat;
1450 
1451 		/* The page was split under us? */
1452 		if (compound_head(page) != head) {
1453 			put_page(head);
1454 			goto repeat;
1455 		}
1456 
1457 		/*
1458 		 * Has the page moved?
1459 		 * This is part of the lockless pagecache protocol. See
1460 		 * include/linux/pagemap.h for details.
1461 		 */
1462 		if (unlikely(page != *pagep)) {
1463 			put_page(head);
1464 			goto repeat;
1465 		}
1466 	}
1467 out:
1468 	rcu_read_unlock();
1469 
1470 	return page;
1471 }
1472 EXPORT_SYMBOL(find_get_entry);
1473 
1474 /**
1475  * find_lock_entry - locate, pin and lock a page cache entry
1476  * @mapping: the address_space to search
1477  * @offset: the page cache index
1478  *
1479  * Looks up the page cache slot at @mapping & @offset.  If there is a
1480  * page cache page, it is returned locked and with an increased
1481  * refcount.
1482  *
1483  * If the slot holds a shadow entry of a previously evicted page, or a
1484  * swap entry from shmem/tmpfs, it is returned.
1485  *
1486  * Otherwise, %NULL is returned.
1487  *
1488  * find_lock_entry() may sleep.
1489  */
1490 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
1491 {
1492 	struct page *page;
1493 
1494 repeat:
1495 	page = find_get_entry(mapping, offset);
1496 	if (page && !radix_tree_exception(page)) {
1497 		lock_page(page);
1498 		/* Has the page been truncated? */
1499 		if (unlikely(page_mapping(page) != mapping)) {
1500 			unlock_page(page);
1501 			put_page(page);
1502 			goto repeat;
1503 		}
1504 		VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page);
1505 	}
1506 	return page;
1507 }
1508 EXPORT_SYMBOL(find_lock_entry);
1509 
1510 /**
1511  * pagecache_get_page - find and get a page reference
1512  * @mapping: the address_space to search
1513  * @offset: the page index
1514  * @fgp_flags: PCG flags
1515  * @gfp_mask: gfp mask to use for the page cache data page allocation
1516  *
1517  * Looks up the page cache slot at @mapping & @offset.
1518  *
1519  * PCG flags modify how the page is returned.
1520  *
1521  * @fgp_flags can be:
1522  *
1523  * - FGP_ACCESSED: the page will be marked accessed
1524  * - FGP_LOCK: Page is return locked
1525  * - FGP_CREAT: If page is not present then a new page is allocated using
1526  *   @gfp_mask and added to the page cache and the VM's LRU
1527  *   list. The page is returned locked and with an increased
1528  *   refcount. Otherwise, NULL is returned.
1529  *
1530  * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
1531  * if the GFP flags specified for FGP_CREAT are atomic.
1532  *
1533  * If there is a page cache page, it is returned with an increased refcount.
1534  */
1535 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
1536 	int fgp_flags, gfp_t gfp_mask)
1537 {
1538 	struct page *page;
1539 
1540 repeat:
1541 	page = find_get_entry(mapping, offset);
1542 	if (radix_tree_exceptional_entry(page))
1543 		page = NULL;
1544 	if (!page)
1545 		goto no_page;
1546 
1547 	if (fgp_flags & FGP_LOCK) {
1548 		if (fgp_flags & FGP_NOWAIT) {
1549 			if (!trylock_page(page)) {
1550 				put_page(page);
1551 				return NULL;
1552 			}
1553 		} else {
1554 			lock_page(page);
1555 		}
1556 
1557 		/* Has the page been truncated? */
1558 		if (unlikely(page->mapping != mapping)) {
1559 			unlock_page(page);
1560 			put_page(page);
1561 			goto repeat;
1562 		}
1563 		VM_BUG_ON_PAGE(page->index != offset, page);
1564 	}
1565 
1566 	if (page && (fgp_flags & FGP_ACCESSED))
1567 		mark_page_accessed(page);
1568 
1569 no_page:
1570 	if (!page && (fgp_flags & FGP_CREAT)) {
1571 		int err;
1572 		if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
1573 			gfp_mask |= __GFP_WRITE;
1574 		if (fgp_flags & FGP_NOFS)
1575 			gfp_mask &= ~__GFP_FS;
1576 
1577 		page = __page_cache_alloc(gfp_mask);
1578 		if (!page)
1579 			return NULL;
1580 
1581 		if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
1582 			fgp_flags |= FGP_LOCK;
1583 
1584 		/* Init accessed so avoid atomic mark_page_accessed later */
1585 		if (fgp_flags & FGP_ACCESSED)
1586 			__SetPageReferenced(page);
1587 
1588 		err = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
1589 		if (unlikely(err)) {
1590 			put_page(page);
1591 			page = NULL;
1592 			if (err == -EEXIST)
1593 				goto repeat;
1594 		}
1595 	}
1596 
1597 	return page;
1598 }
1599 EXPORT_SYMBOL(pagecache_get_page);
1600 
1601 /**
1602  * find_get_entries - gang pagecache lookup
1603  * @mapping:	The address_space to search
1604  * @start:	The starting page cache index
1605  * @nr_entries:	The maximum number of entries
1606  * @entries:	Where the resulting entries are placed
1607  * @indices:	The cache indices corresponding to the entries in @entries
1608  *
1609  * find_get_entries() will search for and return a group of up to
1610  * @nr_entries entries in the mapping.  The entries are placed at
1611  * @entries.  find_get_entries() takes a reference against any actual
1612  * pages it returns.
1613  *
1614  * The search returns a group of mapping-contiguous page cache entries
1615  * with ascending indexes.  There may be holes in the indices due to
1616  * not-present pages.
1617  *
1618  * Any shadow entries of evicted pages, or swap entries from
1619  * shmem/tmpfs, are included in the returned array.
1620  *
1621  * find_get_entries() returns the number of pages and shadow entries
1622  * which were found.
1623  */
1624 unsigned find_get_entries(struct address_space *mapping,
1625 			  pgoff_t start, unsigned int nr_entries,
1626 			  struct page **entries, pgoff_t *indices)
1627 {
1628 	void **slot;
1629 	unsigned int ret = 0;
1630 	struct radix_tree_iter iter;
1631 
1632 	if (!nr_entries)
1633 		return 0;
1634 
1635 	rcu_read_lock();
1636 	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) {
1637 		struct page *head, *page;
1638 repeat:
1639 		page = radix_tree_deref_slot(slot);
1640 		if (unlikely(!page))
1641 			continue;
1642 		if (radix_tree_exception(page)) {
1643 			if (radix_tree_deref_retry(page)) {
1644 				slot = radix_tree_iter_retry(&iter);
1645 				continue;
1646 			}
1647 			/*
1648 			 * A shadow entry of a recently evicted page, a swap
1649 			 * entry from shmem/tmpfs or a DAX entry.  Return it
1650 			 * without attempting to raise page count.
1651 			 */
1652 			goto export;
1653 		}
1654 
1655 		head = compound_head(page);
1656 		if (!page_cache_get_speculative(head))
1657 			goto repeat;
1658 
1659 		/* The page was split under us? */
1660 		if (compound_head(page) != head) {
1661 			put_page(head);
1662 			goto repeat;
1663 		}
1664 
1665 		/* Has the page moved? */
1666 		if (unlikely(page != *slot)) {
1667 			put_page(head);
1668 			goto repeat;
1669 		}
1670 export:
1671 		indices[ret] = iter.index;
1672 		entries[ret] = page;
1673 		if (++ret == nr_entries)
1674 			break;
1675 	}
1676 	rcu_read_unlock();
1677 	return ret;
1678 }
1679 
1680 /**
1681  * find_get_pages_range - gang pagecache lookup
1682  * @mapping:	The address_space to search
1683  * @start:	The starting page index
1684  * @end:	The final page index (inclusive)
1685  * @nr_pages:	The maximum number of pages
1686  * @pages:	Where the resulting pages are placed
1687  *
1688  * find_get_pages_range() will search for and return a group of up to @nr_pages
1689  * pages in the mapping starting at index @start and up to index @end
1690  * (inclusive).  The pages are placed at @pages.  find_get_pages_range() takes
1691  * a reference against the returned pages.
1692  *
1693  * The search returns a group of mapping-contiguous pages with ascending
1694  * indexes.  There may be holes in the indices due to not-present pages.
1695  * We also update @start to index the next page for the traversal.
1696  *
1697  * find_get_pages_range() returns the number of pages which were found. If this
1698  * number is smaller than @nr_pages, the end of specified range has been
1699  * reached.
1700  */
1701 unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
1702 			      pgoff_t end, unsigned int nr_pages,
1703 			      struct page **pages)
1704 {
1705 	struct radix_tree_iter iter;
1706 	void **slot;
1707 	unsigned ret = 0;
1708 
1709 	if (unlikely(!nr_pages))
1710 		return 0;
1711 
1712 	rcu_read_lock();
1713 	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, *start) {
1714 		struct page *head, *page;
1715 
1716 		if (iter.index > end)
1717 			break;
1718 repeat:
1719 		page = radix_tree_deref_slot(slot);
1720 		if (unlikely(!page))
1721 			continue;
1722 
1723 		if (radix_tree_exception(page)) {
1724 			if (radix_tree_deref_retry(page)) {
1725 				slot = radix_tree_iter_retry(&iter);
1726 				continue;
1727 			}
1728 			/*
1729 			 * A shadow entry of a recently evicted page,
1730 			 * or a swap entry from shmem/tmpfs.  Skip
1731 			 * over it.
1732 			 */
1733 			continue;
1734 		}
1735 
1736 		head = compound_head(page);
1737 		if (!page_cache_get_speculative(head))
1738 			goto repeat;
1739 
1740 		/* The page was split under us? */
1741 		if (compound_head(page) != head) {
1742 			put_page(head);
1743 			goto repeat;
1744 		}
1745 
1746 		/* Has the page moved? */
1747 		if (unlikely(page != *slot)) {
1748 			put_page(head);
1749 			goto repeat;
1750 		}
1751 
1752 		pages[ret] = page;
1753 		if (++ret == nr_pages) {
1754 			*start = pages[ret - 1]->index + 1;
1755 			goto out;
1756 		}
1757 	}
1758 
1759 	/*
1760 	 * We come here when there is no page beyond @end. We take care to not
1761 	 * overflow the index @start as it confuses some of the callers. This
1762 	 * breaks the iteration when there is page at index -1 but that is
1763 	 * already broken anyway.
1764 	 */
1765 	if (end == (pgoff_t)-1)
1766 		*start = (pgoff_t)-1;
1767 	else
1768 		*start = end + 1;
1769 out:
1770 	rcu_read_unlock();
1771 
1772 	return ret;
1773 }
1774 
1775 /**
1776  * find_get_pages_contig - gang contiguous pagecache lookup
1777  * @mapping:	The address_space to search
1778  * @index:	The starting page index
1779  * @nr_pages:	The maximum number of pages
1780  * @pages:	Where the resulting pages are placed
1781  *
1782  * find_get_pages_contig() works exactly like find_get_pages(), except
1783  * that the returned number of pages are guaranteed to be contiguous.
1784  *
1785  * find_get_pages_contig() returns the number of pages which were found.
1786  */
1787 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
1788 			       unsigned int nr_pages, struct page **pages)
1789 {
1790 	struct radix_tree_iter iter;
1791 	void **slot;
1792 	unsigned int ret = 0;
1793 
1794 	if (unlikely(!nr_pages))
1795 		return 0;
1796 
1797 	rcu_read_lock();
1798 	radix_tree_for_each_contig(slot, &mapping->i_pages, &iter, index) {
1799 		struct page *head, *page;
1800 repeat:
1801 		page = radix_tree_deref_slot(slot);
1802 		/* The hole, there no reason to continue */
1803 		if (unlikely(!page))
1804 			break;
1805 
1806 		if (radix_tree_exception(page)) {
1807 			if (radix_tree_deref_retry(page)) {
1808 				slot = radix_tree_iter_retry(&iter);
1809 				continue;
1810 			}
1811 			/*
1812 			 * A shadow entry of a recently evicted page,
1813 			 * or a swap entry from shmem/tmpfs.  Stop
1814 			 * looking for contiguous pages.
1815 			 */
1816 			break;
1817 		}
1818 
1819 		head = compound_head(page);
1820 		if (!page_cache_get_speculative(head))
1821 			goto repeat;
1822 
1823 		/* The page was split under us? */
1824 		if (compound_head(page) != head) {
1825 			put_page(head);
1826 			goto repeat;
1827 		}
1828 
1829 		/* Has the page moved? */
1830 		if (unlikely(page != *slot)) {
1831 			put_page(head);
1832 			goto repeat;
1833 		}
1834 
1835 		/*
1836 		 * must check mapping and index after taking the ref.
1837 		 * otherwise we can get both false positives and false
1838 		 * negatives, which is just confusing to the caller.
1839 		 */
1840 		if (page->mapping == NULL || page_to_pgoff(page) != iter.index) {
1841 			put_page(page);
1842 			break;
1843 		}
1844 
1845 		pages[ret] = page;
1846 		if (++ret == nr_pages)
1847 			break;
1848 	}
1849 	rcu_read_unlock();
1850 	return ret;
1851 }
1852 EXPORT_SYMBOL(find_get_pages_contig);
1853 
1854 /**
1855  * find_get_pages_range_tag - find and return pages in given range matching @tag
1856  * @mapping:	the address_space to search
1857  * @index:	the starting page index
1858  * @end:	The final page index (inclusive)
1859  * @tag:	the tag index
1860  * @nr_pages:	the maximum number of pages
1861  * @pages:	where the resulting pages are placed
1862  *
1863  * Like find_get_pages, except we only return pages which are tagged with
1864  * @tag.   We update @index to index the next page for the traversal.
1865  */
1866 unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
1867 			pgoff_t end, int tag, unsigned int nr_pages,
1868 			struct page **pages)
1869 {
1870 	struct radix_tree_iter iter;
1871 	void **slot;
1872 	unsigned ret = 0;
1873 
1874 	if (unlikely(!nr_pages))
1875 		return 0;
1876 
1877 	rcu_read_lock();
1878 	radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter, *index, tag) {
1879 		struct page *head, *page;
1880 
1881 		if (iter.index > end)
1882 			break;
1883 repeat:
1884 		page = radix_tree_deref_slot(slot);
1885 		if (unlikely(!page))
1886 			continue;
1887 
1888 		if (radix_tree_exception(page)) {
1889 			if (radix_tree_deref_retry(page)) {
1890 				slot = radix_tree_iter_retry(&iter);
1891 				continue;
1892 			}
1893 			/*
1894 			 * A shadow entry of a recently evicted page.
1895 			 *
1896 			 * Those entries should never be tagged, but
1897 			 * this tree walk is lockless and the tags are
1898 			 * looked up in bulk, one radix tree node at a
1899 			 * time, so there is a sizable window for page
1900 			 * reclaim to evict a page we saw tagged.
1901 			 *
1902 			 * Skip over it.
1903 			 */
1904 			continue;
1905 		}
1906 
1907 		head = compound_head(page);
1908 		if (!page_cache_get_speculative(head))
1909 			goto repeat;
1910 
1911 		/* The page was split under us? */
1912 		if (compound_head(page) != head) {
1913 			put_page(head);
1914 			goto repeat;
1915 		}
1916 
1917 		/* Has the page moved? */
1918 		if (unlikely(page != *slot)) {
1919 			put_page(head);
1920 			goto repeat;
1921 		}
1922 
1923 		pages[ret] = page;
1924 		if (++ret == nr_pages) {
1925 			*index = pages[ret - 1]->index + 1;
1926 			goto out;
1927 		}
1928 	}
1929 
1930 	/*
1931 	 * We come here when we got at @end. We take care to not overflow the
1932 	 * index @index as it confuses some of the callers. This breaks the
1933 	 * iteration when there is page at index -1 but that is already broken
1934 	 * anyway.
1935 	 */
1936 	if (end == (pgoff_t)-1)
1937 		*index = (pgoff_t)-1;
1938 	else
1939 		*index = end + 1;
1940 out:
1941 	rcu_read_unlock();
1942 
1943 	return ret;
1944 }
1945 EXPORT_SYMBOL(find_get_pages_range_tag);
1946 
1947 /**
1948  * find_get_entries_tag - find and return entries that match @tag
1949  * @mapping:	the address_space to search
1950  * @start:	the starting page cache index
1951  * @tag:	the tag index
1952  * @nr_entries:	the maximum number of entries
1953  * @entries:	where the resulting entries are placed
1954  * @indices:	the cache indices corresponding to the entries in @entries
1955  *
1956  * Like find_get_entries, except we only return entries which are tagged with
1957  * @tag.
1958  */
1959 unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
1960 			int tag, unsigned int nr_entries,
1961 			struct page **entries, pgoff_t *indices)
1962 {
1963 	void **slot;
1964 	unsigned int ret = 0;
1965 	struct radix_tree_iter iter;
1966 
1967 	if (!nr_entries)
1968 		return 0;
1969 
1970 	rcu_read_lock();
1971 	radix_tree_for_each_tagged(slot, &mapping->i_pages, &iter, start, tag) {
1972 		struct page *head, *page;
1973 repeat:
1974 		page = radix_tree_deref_slot(slot);
1975 		if (unlikely(!page))
1976 			continue;
1977 		if (radix_tree_exception(page)) {
1978 			if (radix_tree_deref_retry(page)) {
1979 				slot = radix_tree_iter_retry(&iter);
1980 				continue;
1981 			}
1982 
1983 			/*
1984 			 * A shadow entry of a recently evicted page, a swap
1985 			 * entry from shmem/tmpfs or a DAX entry.  Return it
1986 			 * without attempting to raise page count.
1987 			 */
1988 			goto export;
1989 		}
1990 
1991 		head = compound_head(page);
1992 		if (!page_cache_get_speculative(head))
1993 			goto repeat;
1994 
1995 		/* The page was split under us? */
1996 		if (compound_head(page) != head) {
1997 			put_page(head);
1998 			goto repeat;
1999 		}
2000 
2001 		/* Has the page moved? */
2002 		if (unlikely(page != *slot)) {
2003 			put_page(head);
2004 			goto repeat;
2005 		}
2006 export:
2007 		indices[ret] = iter.index;
2008 		entries[ret] = page;
2009 		if (++ret == nr_entries)
2010 			break;
2011 	}
2012 	rcu_read_unlock();
2013 	return ret;
2014 }
2015 EXPORT_SYMBOL(find_get_entries_tag);
2016 
2017 /*
2018  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
2019  * a _large_ part of the i/o request. Imagine the worst scenario:
2020  *
2021  *      ---R__________________________________________B__________
2022  *         ^ reading here                             ^ bad block(assume 4k)
2023  *
2024  * read(R) => miss => readahead(R...B) => media error => frustrating retries
2025  * => failing the whole request => read(R) => read(R+1) =>
2026  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
2027  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
2028  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
2029  *
2030  * It is going insane. Fix it by quickly scaling down the readahead size.
2031  */
2032 static void shrink_readahead_size_eio(struct file *filp,
2033 					struct file_ra_state *ra)
2034 {
2035 	ra->ra_pages /= 4;
2036 }
2037 
2038 /**
2039  * generic_file_buffered_read - generic file read routine
2040  * @iocb:	the iocb to read
2041  * @iter:	data destination
2042  * @written:	already copied
2043  *
2044  * This is a generic file read routine, and uses the
2045  * mapping->a_ops->readpage() function for the actual low-level stuff.
2046  *
2047  * This is really ugly. But the goto's actually try to clarify some
2048  * of the logic when it comes to error handling etc.
2049  */
2050 static ssize_t generic_file_buffered_read(struct kiocb *iocb,
2051 		struct iov_iter *iter, ssize_t written)
2052 {
2053 	struct file *filp = iocb->ki_filp;
2054 	struct address_space *mapping = filp->f_mapping;
2055 	struct inode *inode = mapping->host;
2056 	struct file_ra_state *ra = &filp->f_ra;
2057 	loff_t *ppos = &iocb->ki_pos;
2058 	pgoff_t index;
2059 	pgoff_t last_index;
2060 	pgoff_t prev_index;
2061 	unsigned long offset;      /* offset into pagecache page */
2062 	unsigned int prev_offset;
2063 	int error = 0;
2064 
2065 	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
2066 		return 0;
2067 	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
2068 
2069 	index = *ppos >> PAGE_SHIFT;
2070 	prev_index = ra->prev_pos >> PAGE_SHIFT;
2071 	prev_offset = ra->prev_pos & (PAGE_SIZE-1);
2072 	last_index = (*ppos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
2073 	offset = *ppos & ~PAGE_MASK;
2074 
2075 	for (;;) {
2076 		struct page *page;
2077 		pgoff_t end_index;
2078 		loff_t isize;
2079 		unsigned long nr, ret;
2080 
2081 		cond_resched();
2082 find_page:
2083 		if (fatal_signal_pending(current)) {
2084 			error = -EINTR;
2085 			goto out;
2086 		}
2087 
2088 		page = find_get_page(mapping, index);
2089 		if (!page) {
2090 			if (iocb->ki_flags & IOCB_NOWAIT)
2091 				goto would_block;
2092 			page_cache_sync_readahead(mapping,
2093 					ra, filp,
2094 					index, last_index - index);
2095 			page = find_get_page(mapping, index);
2096 			if (unlikely(page == NULL))
2097 				goto no_cached_page;
2098 		}
2099 		if (PageReadahead(page)) {
2100 			page_cache_async_readahead(mapping,
2101 					ra, filp, page,
2102 					index, last_index - index);
2103 		}
2104 		if (!PageUptodate(page)) {
2105 			if (iocb->ki_flags & IOCB_NOWAIT) {
2106 				put_page(page);
2107 				goto would_block;
2108 			}
2109 
2110 			/*
2111 			 * See comment in do_read_cache_page on why
2112 			 * wait_on_page_locked is used to avoid unnecessarily
2113 			 * serialisations and why it's safe.
2114 			 */
2115 			error = wait_on_page_locked_killable(page);
2116 			if (unlikely(error))
2117 				goto readpage_error;
2118 			if (PageUptodate(page))
2119 				goto page_ok;
2120 
2121 			if (inode->i_blkbits == PAGE_SHIFT ||
2122 					!mapping->a_ops->is_partially_uptodate)
2123 				goto page_not_up_to_date;
2124 			/* pipes can't handle partially uptodate pages */
2125 			if (unlikely(iter->type & ITER_PIPE))
2126 				goto page_not_up_to_date;
2127 			if (!trylock_page(page))
2128 				goto page_not_up_to_date;
2129 			/* Did it get truncated before we got the lock? */
2130 			if (!page->mapping)
2131 				goto page_not_up_to_date_locked;
2132 			if (!mapping->a_ops->is_partially_uptodate(page,
2133 							offset, iter->count))
2134 				goto page_not_up_to_date_locked;
2135 			unlock_page(page);
2136 		}
2137 page_ok:
2138 		/*
2139 		 * i_size must be checked after we know the page is Uptodate.
2140 		 *
2141 		 * Checking i_size after the check allows us to calculate
2142 		 * the correct value for "nr", which means the zero-filled
2143 		 * part of the page is not copied back to userspace (unless
2144 		 * another truncate extends the file - this is desired though).
2145 		 */
2146 
2147 		isize = i_size_read(inode);
2148 		end_index = (isize - 1) >> PAGE_SHIFT;
2149 		if (unlikely(!isize || index > end_index)) {
2150 			put_page(page);
2151 			goto out;
2152 		}
2153 
2154 		/* nr is the maximum number of bytes to copy from this page */
2155 		nr = PAGE_SIZE;
2156 		if (index == end_index) {
2157 			nr = ((isize - 1) & ~PAGE_MASK) + 1;
2158 			if (nr <= offset) {
2159 				put_page(page);
2160 				goto out;
2161 			}
2162 		}
2163 		nr = nr - offset;
2164 
2165 		/* If users can be writing to this page using arbitrary
2166 		 * virtual addresses, take care about potential aliasing
2167 		 * before reading the page on the kernel side.
2168 		 */
2169 		if (mapping_writably_mapped(mapping))
2170 			flush_dcache_page(page);
2171 
2172 		/*
2173 		 * When a sequential read accesses a page several times,
2174 		 * only mark it as accessed the first time.
2175 		 */
2176 		if (prev_index != index || offset != prev_offset)
2177 			mark_page_accessed(page);
2178 		prev_index = index;
2179 
2180 		/*
2181 		 * Ok, we have the page, and it's up-to-date, so
2182 		 * now we can copy it to user space...
2183 		 */
2184 
2185 		ret = copy_page_to_iter(page, offset, nr, iter);
2186 		offset += ret;
2187 		index += offset >> PAGE_SHIFT;
2188 		offset &= ~PAGE_MASK;
2189 		prev_offset = offset;
2190 
2191 		put_page(page);
2192 		written += ret;
2193 		if (!iov_iter_count(iter))
2194 			goto out;
2195 		if (ret < nr) {
2196 			error = -EFAULT;
2197 			goto out;
2198 		}
2199 		continue;
2200 
2201 page_not_up_to_date:
2202 		/* Get exclusive access to the page ... */
2203 		error = lock_page_killable(page);
2204 		if (unlikely(error))
2205 			goto readpage_error;
2206 
2207 page_not_up_to_date_locked:
2208 		/* Did it get truncated before we got the lock? */
2209 		if (!page->mapping) {
2210 			unlock_page(page);
2211 			put_page(page);
2212 			continue;
2213 		}
2214 
2215 		/* Did somebody else fill it already? */
2216 		if (PageUptodate(page)) {
2217 			unlock_page(page);
2218 			goto page_ok;
2219 		}
2220 
2221 readpage:
2222 		/*
2223 		 * A previous I/O error may have been due to temporary
2224 		 * failures, eg. multipath errors.
2225 		 * PG_error will be set again if readpage fails.
2226 		 */
2227 		ClearPageError(page);
2228 		/* Start the actual read. The read will unlock the page. */
2229 		error = mapping->a_ops->readpage(filp, page);
2230 
2231 		if (unlikely(error)) {
2232 			if (error == AOP_TRUNCATED_PAGE) {
2233 				put_page(page);
2234 				error = 0;
2235 				goto find_page;
2236 			}
2237 			goto readpage_error;
2238 		}
2239 
2240 		if (!PageUptodate(page)) {
2241 			error = lock_page_killable(page);
2242 			if (unlikely(error))
2243 				goto readpage_error;
2244 			if (!PageUptodate(page)) {
2245 				if (page->mapping == NULL) {
2246 					/*
2247 					 * invalidate_mapping_pages got it
2248 					 */
2249 					unlock_page(page);
2250 					put_page(page);
2251 					goto find_page;
2252 				}
2253 				unlock_page(page);
2254 				shrink_readahead_size_eio(filp, ra);
2255 				error = -EIO;
2256 				goto readpage_error;
2257 			}
2258 			unlock_page(page);
2259 		}
2260 
2261 		goto page_ok;
2262 
2263 readpage_error:
2264 		/* UHHUH! A synchronous read error occurred. Report it */
2265 		put_page(page);
2266 		goto out;
2267 
2268 no_cached_page:
2269 		/*
2270 		 * Ok, it wasn't cached, so we need to create a new
2271 		 * page..
2272 		 */
2273 		page = page_cache_alloc(mapping);
2274 		if (!page) {
2275 			error = -ENOMEM;
2276 			goto out;
2277 		}
2278 		error = add_to_page_cache_lru(page, mapping, index,
2279 				mapping_gfp_constraint(mapping, GFP_KERNEL));
2280 		if (error) {
2281 			put_page(page);
2282 			if (error == -EEXIST) {
2283 				error = 0;
2284 				goto find_page;
2285 			}
2286 			goto out;
2287 		}
2288 		goto readpage;
2289 	}
2290 
2291 would_block:
2292 	error = -EAGAIN;
2293 out:
2294 	ra->prev_pos = prev_index;
2295 	ra->prev_pos <<= PAGE_SHIFT;
2296 	ra->prev_pos |= prev_offset;
2297 
2298 	*ppos = ((loff_t)index << PAGE_SHIFT) + offset;
2299 	file_accessed(filp);
2300 	return written ? written : error;
2301 }
2302 
2303 /**
2304  * generic_file_read_iter - generic filesystem read routine
2305  * @iocb:	kernel I/O control block
2306  * @iter:	destination for the data read
2307  *
2308  * This is the "read_iter()" routine for all filesystems
2309  * that can use the page cache directly.
2310  */
2311 ssize_t
2312 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
2313 {
2314 	size_t count = iov_iter_count(iter);
2315 	ssize_t retval = 0;
2316 
2317 	if (!count)
2318 		goto out; /* skip atime */
2319 
2320 	if (iocb->ki_flags & IOCB_DIRECT) {
2321 		struct file *file = iocb->ki_filp;
2322 		struct address_space *mapping = file->f_mapping;
2323 		struct inode *inode = mapping->host;
2324 		loff_t size;
2325 
2326 		size = i_size_read(inode);
2327 		if (iocb->ki_flags & IOCB_NOWAIT) {
2328 			if (filemap_range_has_page(mapping, iocb->ki_pos,
2329 						   iocb->ki_pos + count - 1))
2330 				return -EAGAIN;
2331 		} else {
2332 			retval = filemap_write_and_wait_range(mapping,
2333 						iocb->ki_pos,
2334 					        iocb->ki_pos + count - 1);
2335 			if (retval < 0)
2336 				goto out;
2337 		}
2338 
2339 		file_accessed(file);
2340 
2341 		retval = mapping->a_ops->direct_IO(iocb, iter);
2342 		if (retval >= 0) {
2343 			iocb->ki_pos += retval;
2344 			count -= retval;
2345 		}
2346 		iov_iter_revert(iter, count - iov_iter_count(iter));
2347 
2348 		/*
2349 		 * Btrfs can have a short DIO read if we encounter
2350 		 * compressed extents, so if there was an error, or if
2351 		 * we've already read everything we wanted to, or if
2352 		 * there was a short read because we hit EOF, go ahead
2353 		 * and return.  Otherwise fallthrough to buffered io for
2354 		 * the rest of the read.  Buffered reads will not work for
2355 		 * DAX files, so don't bother trying.
2356 		 */
2357 		if (retval < 0 || !count || iocb->ki_pos >= size ||
2358 		    IS_DAX(inode))
2359 			goto out;
2360 	}
2361 
2362 	retval = generic_file_buffered_read(iocb, iter, retval);
2363 out:
2364 	return retval;
2365 }
2366 EXPORT_SYMBOL(generic_file_read_iter);
2367 
2368 #ifdef CONFIG_MMU
2369 /**
2370  * page_cache_read - adds requested page to the page cache if not already there
2371  * @file:	file to read
2372  * @offset:	page index
2373  * @gfp_mask:	memory allocation flags
2374  *
2375  * This adds the requested page to the page cache if it isn't already there,
2376  * and schedules an I/O to read in its contents from disk.
2377  */
2378 static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
2379 {
2380 	struct address_space *mapping = file->f_mapping;
2381 	struct page *page;
2382 	int ret;
2383 
2384 	do {
2385 		page = __page_cache_alloc(gfp_mask);
2386 		if (!page)
2387 			return -ENOMEM;
2388 
2389 		ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
2390 		if (ret == 0)
2391 			ret = mapping->a_ops->readpage(file, page);
2392 		else if (ret == -EEXIST)
2393 			ret = 0; /* losing race to add is OK */
2394 
2395 		put_page(page);
2396 
2397 	} while (ret == AOP_TRUNCATED_PAGE);
2398 
2399 	return ret;
2400 }
2401 
2402 #define MMAP_LOTSAMISS  (100)
2403 
2404 /*
2405  * Synchronous readahead happens when we don't even find
2406  * a page in the page cache at all.
2407  */
2408 static void do_sync_mmap_readahead(struct vm_area_struct *vma,
2409 				   struct file_ra_state *ra,
2410 				   struct file *file,
2411 				   pgoff_t offset)
2412 {
2413 	struct address_space *mapping = file->f_mapping;
2414 
2415 	/* If we don't want any read-ahead, don't bother */
2416 	if (vma->vm_flags & VM_RAND_READ)
2417 		return;
2418 	if (!ra->ra_pages)
2419 		return;
2420 
2421 	if (vma->vm_flags & VM_SEQ_READ) {
2422 		page_cache_sync_readahead(mapping, ra, file, offset,
2423 					  ra->ra_pages);
2424 		return;
2425 	}
2426 
2427 	/* Avoid banging the cache line if not needed */
2428 	if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
2429 		ra->mmap_miss++;
2430 
2431 	/*
2432 	 * Do we miss much more than hit in this file? If so,
2433 	 * stop bothering with read-ahead. It will only hurt.
2434 	 */
2435 	if (ra->mmap_miss > MMAP_LOTSAMISS)
2436 		return;
2437 
2438 	/*
2439 	 * mmap read-around
2440 	 */
2441 	ra->start = max_t(long, 0, offset - ra->ra_pages / 2);
2442 	ra->size = ra->ra_pages;
2443 	ra->async_size = ra->ra_pages / 4;
2444 	ra_submit(ra, mapping, file);
2445 }
2446 
2447 /*
2448  * Asynchronous readahead happens when we find the page and PG_readahead,
2449  * so we want to possibly extend the readahead further..
2450  */
2451 static void do_async_mmap_readahead(struct vm_area_struct *vma,
2452 				    struct file_ra_state *ra,
2453 				    struct file *file,
2454 				    struct page *page,
2455 				    pgoff_t offset)
2456 {
2457 	struct address_space *mapping = file->f_mapping;
2458 
2459 	/* If we don't want any read-ahead, don't bother */
2460 	if (vma->vm_flags & VM_RAND_READ)
2461 		return;
2462 	if (ra->mmap_miss > 0)
2463 		ra->mmap_miss--;
2464 	if (PageReadahead(page))
2465 		page_cache_async_readahead(mapping, ra, file,
2466 					   page, offset, ra->ra_pages);
2467 }
2468 
2469 /**
2470  * filemap_fault - read in file data for page fault handling
2471  * @vmf:	struct vm_fault containing details of the fault
2472  *
2473  * filemap_fault() is invoked via the vma operations vector for a
2474  * mapped memory region to read in file data during a page fault.
2475  *
2476  * The goto's are kind of ugly, but this streamlines the normal case of having
2477  * it in the page cache, and handles the special cases reasonably without
2478  * having a lot of duplicated code.
2479  *
2480  * vma->vm_mm->mmap_sem must be held on entry.
2481  *
2482  * If our return value has VM_FAULT_RETRY set, it's because
2483  * lock_page_or_retry() returned 0.
2484  * The mmap_sem has usually been released in this case.
2485  * See __lock_page_or_retry() for the exception.
2486  *
2487  * If our return value does not have VM_FAULT_RETRY set, the mmap_sem
2488  * has not been released.
2489  *
2490  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
2491  */
2492 int filemap_fault(struct vm_fault *vmf)
2493 {
2494 	int error;
2495 	struct file *file = vmf->vma->vm_file;
2496 	struct address_space *mapping = file->f_mapping;
2497 	struct file_ra_state *ra = &file->f_ra;
2498 	struct inode *inode = mapping->host;
2499 	pgoff_t offset = vmf->pgoff;
2500 	pgoff_t max_off;
2501 	struct page *page;
2502 	int ret = 0;
2503 
2504 	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
2505 	if (unlikely(offset >= max_off))
2506 		return VM_FAULT_SIGBUS;
2507 
2508 	/*
2509 	 * Do we have something in the page cache already?
2510 	 */
2511 	page = find_get_page(mapping, offset);
2512 	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
2513 		/*
2514 		 * We found the page, so try async readahead before
2515 		 * waiting for the lock.
2516 		 */
2517 		do_async_mmap_readahead(vmf->vma, ra, file, page, offset);
2518 	} else if (!page) {
2519 		/* No page in the page cache at all */
2520 		do_sync_mmap_readahead(vmf->vma, ra, file, offset);
2521 		count_vm_event(PGMAJFAULT);
2522 		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
2523 		ret = VM_FAULT_MAJOR;
2524 retry_find:
2525 		page = find_get_page(mapping, offset);
2526 		if (!page)
2527 			goto no_cached_page;
2528 	}
2529 
2530 	if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
2531 		put_page(page);
2532 		return ret | VM_FAULT_RETRY;
2533 	}
2534 
2535 	/* Did it get truncated? */
2536 	if (unlikely(page->mapping != mapping)) {
2537 		unlock_page(page);
2538 		put_page(page);
2539 		goto retry_find;
2540 	}
2541 	VM_BUG_ON_PAGE(page->index != offset, page);
2542 
2543 	/*
2544 	 * We have a locked page in the page cache, now we need to check
2545 	 * that it's up-to-date. If not, it is going to be due to an error.
2546 	 */
2547 	if (unlikely(!PageUptodate(page)))
2548 		goto page_not_uptodate;
2549 
2550 	/*
2551 	 * Found the page and have a reference on it.
2552 	 * We must recheck i_size under page lock.
2553 	 */
2554 	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
2555 	if (unlikely(offset >= max_off)) {
2556 		unlock_page(page);
2557 		put_page(page);
2558 		return VM_FAULT_SIGBUS;
2559 	}
2560 
2561 	vmf->page = page;
2562 	return ret | VM_FAULT_LOCKED;
2563 
2564 no_cached_page:
2565 	/*
2566 	 * We're only likely to ever get here if MADV_RANDOM is in
2567 	 * effect.
2568 	 */
2569 	error = page_cache_read(file, offset, vmf->gfp_mask);
2570 
2571 	/*
2572 	 * The page we want has now been added to the page cache.
2573 	 * In the unlikely event that someone removed it in the
2574 	 * meantime, we'll just come back here and read it again.
2575 	 */
2576 	if (error >= 0)
2577 		goto retry_find;
2578 
2579 	/*
2580 	 * An error return from page_cache_read can result if the
2581 	 * system is low on memory, or a problem occurs while trying
2582 	 * to schedule I/O.
2583 	 */
2584 	if (error == -ENOMEM)
2585 		return VM_FAULT_OOM;
2586 	return VM_FAULT_SIGBUS;
2587 
2588 page_not_uptodate:
2589 	/*
2590 	 * Umm, take care of errors if the page isn't up-to-date.
2591 	 * Try to re-read it _once_. We do this synchronously,
2592 	 * because there really aren't any performance issues here
2593 	 * and we need to check for errors.
2594 	 */
2595 	ClearPageError(page);
2596 	error = mapping->a_ops->readpage(file, page);
2597 	if (!error) {
2598 		wait_on_page_locked(page);
2599 		if (!PageUptodate(page))
2600 			error = -EIO;
2601 	}
2602 	put_page(page);
2603 
2604 	if (!error || error == AOP_TRUNCATED_PAGE)
2605 		goto retry_find;
2606 
2607 	/* Things didn't work out. Return zero to tell the mm layer so. */
2608 	shrink_readahead_size_eio(file, ra);
2609 	return VM_FAULT_SIGBUS;
2610 }
2611 EXPORT_SYMBOL(filemap_fault);
2612 
2613 void filemap_map_pages(struct vm_fault *vmf,
2614 		pgoff_t start_pgoff, pgoff_t end_pgoff)
2615 {
2616 	struct radix_tree_iter iter;
2617 	void **slot;
2618 	struct file *file = vmf->vma->vm_file;
2619 	struct address_space *mapping = file->f_mapping;
2620 	pgoff_t last_pgoff = start_pgoff;
2621 	unsigned long max_idx;
2622 	struct page *head, *page;
2623 
2624 	rcu_read_lock();
2625 	radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start_pgoff) {
2626 		if (iter.index > end_pgoff)
2627 			break;
2628 repeat:
2629 		page = radix_tree_deref_slot(slot);
2630 		if (unlikely(!page))
2631 			goto next;
2632 		if (radix_tree_exception(page)) {
2633 			if (radix_tree_deref_retry(page)) {
2634 				slot = radix_tree_iter_retry(&iter);
2635 				continue;
2636 			}
2637 			goto next;
2638 		}
2639 
2640 		head = compound_head(page);
2641 		if (!page_cache_get_speculative(head))
2642 			goto repeat;
2643 
2644 		/* The page was split under us? */
2645 		if (compound_head(page) != head) {
2646 			put_page(head);
2647 			goto repeat;
2648 		}
2649 
2650 		/* Has the page moved? */
2651 		if (unlikely(page != *slot)) {
2652 			put_page(head);
2653 			goto repeat;
2654 		}
2655 
2656 		if (!PageUptodate(page) ||
2657 				PageReadahead(page) ||
2658 				PageHWPoison(page))
2659 			goto skip;
2660 		if (!trylock_page(page))
2661 			goto skip;
2662 
2663 		if (page->mapping != mapping || !PageUptodate(page))
2664 			goto unlock;
2665 
2666 		max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
2667 		if (page->index >= max_idx)
2668 			goto unlock;
2669 
2670 		if (file->f_ra.mmap_miss > 0)
2671 			file->f_ra.mmap_miss--;
2672 
2673 		vmf->address += (iter.index - last_pgoff) << PAGE_SHIFT;
2674 		if (vmf->pte)
2675 			vmf->pte += iter.index - last_pgoff;
2676 		last_pgoff = iter.index;
2677 		if (alloc_set_pte(vmf, NULL, page))
2678 			goto unlock;
2679 		unlock_page(page);
2680 		goto next;
2681 unlock:
2682 		unlock_page(page);
2683 skip:
2684 		put_page(page);
2685 next:
2686 		/* Huge page is mapped? No need to proceed. */
2687 		if (pmd_trans_huge(*vmf->pmd))
2688 			break;
2689 		if (iter.index == end_pgoff)
2690 			break;
2691 	}
2692 	rcu_read_unlock();
2693 }
2694 EXPORT_SYMBOL(filemap_map_pages);
2695 
2696 int filemap_page_mkwrite(struct vm_fault *vmf)
2697 {
2698 	struct page *page = vmf->page;
2699 	struct inode *inode = file_inode(vmf->vma->vm_file);
2700 	int ret = VM_FAULT_LOCKED;
2701 
2702 	sb_start_pagefault(inode->i_sb);
2703 	file_update_time(vmf->vma->vm_file);
2704 	lock_page(page);
2705 	if (page->mapping != inode->i_mapping) {
2706 		unlock_page(page);
2707 		ret = VM_FAULT_NOPAGE;
2708 		goto out;
2709 	}
2710 	/*
2711 	 * We mark the page dirty already here so that when freeze is in
2712 	 * progress, we are guaranteed that writeback during freezing will
2713 	 * see the dirty page and writeprotect it again.
2714 	 */
2715 	set_page_dirty(page);
2716 	wait_for_stable_page(page);
2717 out:
2718 	sb_end_pagefault(inode->i_sb);
2719 	return ret;
2720 }
2721 
2722 const struct vm_operations_struct generic_file_vm_ops = {
2723 	.fault		= filemap_fault,
2724 	.map_pages	= filemap_map_pages,
2725 	.page_mkwrite	= filemap_page_mkwrite,
2726 };
2727 
2728 /* This is used for a general mmap of a disk file */
2729 
2730 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2731 {
2732 	struct address_space *mapping = file->f_mapping;
2733 
2734 	if (!mapping->a_ops->readpage)
2735 		return -ENOEXEC;
2736 	file_accessed(file);
2737 	vma->vm_ops = &generic_file_vm_ops;
2738 	return 0;
2739 }
2740 
2741 /*
2742  * This is for filesystems which do not implement ->writepage.
2743  */
2744 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
2745 {
2746 	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
2747 		return -EINVAL;
2748 	return generic_file_mmap(file, vma);
2749 }
2750 #else
2751 int filemap_page_mkwrite(struct vm_fault *vmf)
2752 {
2753 	return -ENOSYS;
2754 }
2755 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2756 {
2757 	return -ENOSYS;
2758 }
2759 int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
2760 {
2761 	return -ENOSYS;
2762 }
2763 #endif /* CONFIG_MMU */
2764 
2765 EXPORT_SYMBOL(filemap_page_mkwrite);
2766 EXPORT_SYMBOL(generic_file_mmap);
2767 EXPORT_SYMBOL(generic_file_readonly_mmap);
2768 
2769 static struct page *wait_on_page_read(struct page *page)
2770 {
2771 	if (!IS_ERR(page)) {
2772 		wait_on_page_locked(page);
2773 		if (!PageUptodate(page)) {
2774 			put_page(page);
2775 			page = ERR_PTR(-EIO);
2776 		}
2777 	}
2778 	return page;
2779 }
2780 
2781 static struct page *do_read_cache_page(struct address_space *mapping,
2782 				pgoff_t index,
2783 				int (*filler)(void *, struct page *),
2784 				void *data,
2785 				gfp_t gfp)
2786 {
2787 	struct page *page;
2788 	int err;
2789 repeat:
2790 	page = find_get_page(mapping, index);
2791 	if (!page) {
2792 		page = __page_cache_alloc(gfp);
2793 		if (!page)
2794 			return ERR_PTR(-ENOMEM);
2795 		err = add_to_page_cache_lru(page, mapping, index, gfp);
2796 		if (unlikely(err)) {
2797 			put_page(page);
2798 			if (err == -EEXIST)
2799 				goto repeat;
2800 			/* Presumably ENOMEM for radix tree node */
2801 			return ERR_PTR(err);
2802 		}
2803 
2804 filler:
2805 		err = filler(data, page);
2806 		if (err < 0) {
2807 			put_page(page);
2808 			return ERR_PTR(err);
2809 		}
2810 
2811 		page = wait_on_page_read(page);
2812 		if (IS_ERR(page))
2813 			return page;
2814 		goto out;
2815 	}
2816 	if (PageUptodate(page))
2817 		goto out;
2818 
2819 	/*
2820 	 * Page is not up to date and may be locked due one of the following
2821 	 * case a: Page is being filled and the page lock is held
2822 	 * case b: Read/write error clearing the page uptodate status
2823 	 * case c: Truncation in progress (page locked)
2824 	 * case d: Reclaim in progress
2825 	 *
2826 	 * Case a, the page will be up to date when the page is unlocked.
2827 	 *    There is no need to serialise on the page lock here as the page
2828 	 *    is pinned so the lock gives no additional protection. Even if the
2829 	 *    the page is truncated, the data is still valid if PageUptodate as
2830 	 *    it's a race vs truncate race.
2831 	 * Case b, the page will not be up to date
2832 	 * Case c, the page may be truncated but in itself, the data may still
2833 	 *    be valid after IO completes as it's a read vs truncate race. The
2834 	 *    operation must restart if the page is not uptodate on unlock but
2835 	 *    otherwise serialising on page lock to stabilise the mapping gives
2836 	 *    no additional guarantees to the caller as the page lock is
2837 	 *    released before return.
2838 	 * Case d, similar to truncation. If reclaim holds the page lock, it
2839 	 *    will be a race with remove_mapping that determines if the mapping
2840 	 *    is valid on unlock but otherwise the data is valid and there is
2841 	 *    no need to serialise with page lock.
2842 	 *
2843 	 * As the page lock gives no additional guarantee, we optimistically
2844 	 * wait on the page to be unlocked and check if it's up to date and
2845 	 * use the page if it is. Otherwise, the page lock is required to
2846 	 * distinguish between the different cases. The motivation is that we
2847 	 * avoid spurious serialisations and wakeups when multiple processes
2848 	 * wait on the same page for IO to complete.
2849 	 */
2850 	wait_on_page_locked(page);
2851 	if (PageUptodate(page))
2852 		goto out;
2853 
2854 	/* Distinguish between all the cases under the safety of the lock */
2855 	lock_page(page);
2856 
2857 	/* Case c or d, restart the operation */
2858 	if (!page->mapping) {
2859 		unlock_page(page);
2860 		put_page(page);
2861 		goto repeat;
2862 	}
2863 
2864 	/* Someone else locked and filled the page in a very small window */
2865 	if (PageUptodate(page)) {
2866 		unlock_page(page);
2867 		goto out;
2868 	}
2869 	goto filler;
2870 
2871 out:
2872 	mark_page_accessed(page);
2873 	return page;
2874 }
2875 
2876 /**
2877  * read_cache_page - read into page cache, fill it if needed
2878  * @mapping:	the page's address_space
2879  * @index:	the page index
2880  * @filler:	function to perform the read
2881  * @data:	first arg to filler(data, page) function, often left as NULL
2882  *
2883  * Read into the page cache. If a page already exists, and PageUptodate() is
2884  * not set, try to fill the page and wait for it to become unlocked.
2885  *
2886  * If the page does not get brought uptodate, return -EIO.
2887  */
2888 struct page *read_cache_page(struct address_space *mapping,
2889 				pgoff_t index,
2890 				int (*filler)(void *, struct page *),
2891 				void *data)
2892 {
2893 	return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
2894 }
2895 EXPORT_SYMBOL(read_cache_page);
2896 
2897 /**
2898  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
2899  * @mapping:	the page's address_space
2900  * @index:	the page index
2901  * @gfp:	the page allocator flags to use if allocating
2902  *
2903  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
2904  * any new page allocations done using the specified allocation flags.
2905  *
2906  * If the page does not get brought uptodate, return -EIO.
2907  */
2908 struct page *read_cache_page_gfp(struct address_space *mapping,
2909 				pgoff_t index,
2910 				gfp_t gfp)
2911 {
2912 	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
2913 
2914 	return do_read_cache_page(mapping, index, filler, NULL, gfp);
2915 }
2916 EXPORT_SYMBOL(read_cache_page_gfp);
2917 
2918 /*
2919  * Performs necessary checks before doing a write
2920  *
2921  * Can adjust writing position or amount of bytes to write.
2922  * Returns appropriate error code that caller should return or
2923  * zero in case that write should be allowed.
2924  */
2925 inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
2926 {
2927 	struct file *file = iocb->ki_filp;
2928 	struct inode *inode = file->f_mapping->host;
2929 	unsigned long limit = rlimit(RLIMIT_FSIZE);
2930 	loff_t pos;
2931 
2932 	if (!iov_iter_count(from))
2933 		return 0;
2934 
2935 	/* FIXME: this is for backwards compatibility with 2.4 */
2936 	if (iocb->ki_flags & IOCB_APPEND)
2937 		iocb->ki_pos = i_size_read(inode);
2938 
2939 	pos = iocb->ki_pos;
2940 
2941 	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
2942 		return -EINVAL;
2943 
2944 	if (limit != RLIM_INFINITY) {
2945 		if (iocb->ki_pos >= limit) {
2946 			send_sig(SIGXFSZ, current, 0);
2947 			return -EFBIG;
2948 		}
2949 		iov_iter_truncate(from, limit - (unsigned long)pos);
2950 	}
2951 
2952 	/*
2953 	 * LFS rule
2954 	 */
2955 	if (unlikely(pos + iov_iter_count(from) > MAX_NON_LFS &&
2956 				!(file->f_flags & O_LARGEFILE))) {
2957 		if (pos >= MAX_NON_LFS)
2958 			return -EFBIG;
2959 		iov_iter_truncate(from, MAX_NON_LFS - (unsigned long)pos);
2960 	}
2961 
2962 	/*
2963 	 * Are we about to exceed the fs block limit ?
2964 	 *
2965 	 * If we have written data it becomes a short write.  If we have
2966 	 * exceeded without writing data we send a signal and return EFBIG.
2967 	 * Linus frestrict idea will clean these up nicely..
2968 	 */
2969 	if (unlikely(pos >= inode->i_sb->s_maxbytes))
2970 		return -EFBIG;
2971 
2972 	iov_iter_truncate(from, inode->i_sb->s_maxbytes - pos);
2973 	return iov_iter_count(from);
2974 }
2975 EXPORT_SYMBOL(generic_write_checks);
2976 
2977 int pagecache_write_begin(struct file *file, struct address_space *mapping,
2978 				loff_t pos, unsigned len, unsigned flags,
2979 				struct page **pagep, void **fsdata)
2980 {
2981 	const struct address_space_operations *aops = mapping->a_ops;
2982 
2983 	return aops->write_begin(file, mapping, pos, len, flags,
2984 							pagep, fsdata);
2985 }
2986 EXPORT_SYMBOL(pagecache_write_begin);
2987 
2988 int pagecache_write_end(struct file *file, struct address_space *mapping,
2989 				loff_t pos, unsigned len, unsigned copied,
2990 				struct page *page, void *fsdata)
2991 {
2992 	const struct address_space_operations *aops = mapping->a_ops;
2993 
2994 	return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2995 }
2996 EXPORT_SYMBOL(pagecache_write_end);
2997 
2998 ssize_t
2999 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
3000 {
3001 	struct file	*file = iocb->ki_filp;
3002 	struct address_space *mapping = file->f_mapping;
3003 	struct inode	*inode = mapping->host;
3004 	loff_t		pos = iocb->ki_pos;
3005 	ssize_t		written;
3006 	size_t		write_len;
3007 	pgoff_t		end;
3008 
3009 	write_len = iov_iter_count(from);
3010 	end = (pos + write_len - 1) >> PAGE_SHIFT;
3011 
3012 	if (iocb->ki_flags & IOCB_NOWAIT) {
3013 		/* If there are pages to writeback, return */
3014 		if (filemap_range_has_page(inode->i_mapping, pos,
3015 					   pos + iov_iter_count(from)))
3016 			return -EAGAIN;
3017 	} else {
3018 		written = filemap_write_and_wait_range(mapping, pos,
3019 							pos + write_len - 1);
3020 		if (written)
3021 			goto out;
3022 	}
3023 
3024 	/*
3025 	 * After a write we want buffered reads to be sure to go to disk to get
3026 	 * the new data.  We invalidate clean cached page from the region we're
3027 	 * about to write.  We do this *before* the write so that we can return
3028 	 * without clobbering -EIOCBQUEUED from ->direct_IO().
3029 	 */
3030 	written = invalidate_inode_pages2_range(mapping,
3031 					pos >> PAGE_SHIFT, end);
3032 	/*
3033 	 * If a page can not be invalidated, return 0 to fall back
3034 	 * to buffered write.
3035 	 */
3036 	if (written) {
3037 		if (written == -EBUSY)
3038 			return 0;
3039 		goto out;
3040 	}
3041 
3042 	written = mapping->a_ops->direct_IO(iocb, from);
3043 
3044 	/*
3045 	 * Finally, try again to invalidate clean pages which might have been
3046 	 * cached by non-direct readahead, or faulted in by get_user_pages()
3047 	 * if the source of the write was an mmap'ed region of the file
3048 	 * we're writing.  Either one is a pretty crazy thing to do,
3049 	 * so we don't support it 100%.  If this invalidation
3050 	 * fails, tough, the write still worked...
3051 	 *
3052 	 * Most of the time we do not need this since dio_complete() will do
3053 	 * the invalidation for us. However there are some file systems that
3054 	 * do not end up with dio_complete() being called, so let's not break
3055 	 * them by removing it completely
3056 	 */
3057 	if (mapping->nrpages)
3058 		invalidate_inode_pages2_range(mapping,
3059 					pos >> PAGE_SHIFT, end);
3060 
3061 	if (written > 0) {
3062 		pos += written;
3063 		write_len -= written;
3064 		if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
3065 			i_size_write(inode, pos);
3066 			mark_inode_dirty(inode);
3067 		}
3068 		iocb->ki_pos = pos;
3069 	}
3070 	iov_iter_revert(from, write_len - iov_iter_count(from));
3071 out:
3072 	return written;
3073 }
3074 EXPORT_SYMBOL(generic_file_direct_write);
3075 
3076 /*
3077  * Find or create a page at the given pagecache position. Return the locked
3078  * page. This function is specifically for buffered writes.
3079  */
3080 struct page *grab_cache_page_write_begin(struct address_space *mapping,
3081 					pgoff_t index, unsigned flags)
3082 {
3083 	struct page *page;
3084 	int fgp_flags = FGP_LOCK|FGP_WRITE|FGP_CREAT;
3085 
3086 	if (flags & AOP_FLAG_NOFS)
3087 		fgp_flags |= FGP_NOFS;
3088 
3089 	page = pagecache_get_page(mapping, index, fgp_flags,
3090 			mapping_gfp_mask(mapping));
3091 	if (page)
3092 		wait_for_stable_page(page);
3093 
3094 	return page;
3095 }
3096 EXPORT_SYMBOL(grab_cache_page_write_begin);
3097 
3098 ssize_t generic_perform_write(struct file *file,
3099 				struct iov_iter *i, loff_t pos)
3100 {
3101 	struct address_space *mapping = file->f_mapping;
3102 	const struct address_space_operations *a_ops = mapping->a_ops;
3103 	long status = 0;
3104 	ssize_t written = 0;
3105 	unsigned int flags = 0;
3106 
3107 	do {
3108 		struct page *page;
3109 		unsigned long offset;	/* Offset into pagecache page */
3110 		unsigned long bytes;	/* Bytes to write to page */
3111 		size_t copied;		/* Bytes copied from user */
3112 		void *fsdata;
3113 
3114 		offset = (pos & (PAGE_SIZE - 1));
3115 		bytes = min_t(unsigned long, PAGE_SIZE - offset,
3116 						iov_iter_count(i));
3117 
3118 again:
3119 		/*
3120 		 * Bring in the user page that we will copy from _first_.
3121 		 * Otherwise there's a nasty deadlock on copying from the
3122 		 * same page as we're writing to, without it being marked
3123 		 * up-to-date.
3124 		 *
3125 		 * Not only is this an optimisation, but it is also required
3126 		 * to check that the address is actually valid, when atomic
3127 		 * usercopies are used, below.
3128 		 */
3129 		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
3130 			status = -EFAULT;
3131 			break;
3132 		}
3133 
3134 		if (fatal_signal_pending(current)) {
3135 			status = -EINTR;
3136 			break;
3137 		}
3138 
3139 		status = a_ops->write_begin(file, mapping, pos, bytes, flags,
3140 						&page, &fsdata);
3141 		if (unlikely(status < 0))
3142 			break;
3143 
3144 		if (mapping_writably_mapped(mapping))
3145 			flush_dcache_page(page);
3146 
3147 		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
3148 		flush_dcache_page(page);
3149 
3150 		status = a_ops->write_end(file, mapping, pos, bytes, copied,
3151 						page, fsdata);
3152 		if (unlikely(status < 0))
3153 			break;
3154 		copied = status;
3155 
3156 		cond_resched();
3157 
3158 		iov_iter_advance(i, copied);
3159 		if (unlikely(copied == 0)) {
3160 			/*
3161 			 * If we were unable to copy any data at all, we must
3162 			 * fall back to a single segment length write.
3163 			 *
3164 			 * If we didn't fallback here, we could livelock
3165 			 * because not all segments in the iov can be copied at
3166 			 * once without a pagefault.
3167 			 */
3168 			bytes = min_t(unsigned long, PAGE_SIZE - offset,
3169 						iov_iter_single_seg_count(i));
3170 			goto again;
3171 		}
3172 		pos += copied;
3173 		written += copied;
3174 
3175 		balance_dirty_pages_ratelimited(mapping);
3176 	} while (iov_iter_count(i));
3177 
3178 	return written ? written : status;
3179 }
3180 EXPORT_SYMBOL(generic_perform_write);
3181 
3182 /**
3183  * __generic_file_write_iter - write data to a file
3184  * @iocb:	IO state structure (file, offset, etc.)
3185  * @from:	iov_iter with data to write
3186  *
3187  * This function does all the work needed for actually writing data to a
3188  * file. It does all basic checks, removes SUID from the file, updates
3189  * modification times and calls proper subroutines depending on whether we
3190  * do direct IO or a standard buffered write.
3191  *
3192  * It expects i_mutex to be grabbed unless we work on a block device or similar
3193  * object which does not need locking at all.
3194  *
3195  * This function does *not* take care of syncing data in case of O_SYNC write.
3196  * A caller has to handle it. This is mainly due to the fact that we want to
3197  * avoid syncing under i_mutex.
3198  */
3199 ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
3200 {
3201 	struct file *file = iocb->ki_filp;
3202 	struct address_space * mapping = file->f_mapping;
3203 	struct inode 	*inode = mapping->host;
3204 	ssize_t		written = 0;
3205 	ssize_t		err;
3206 	ssize_t		status;
3207 
3208 	/* We can write back this queue in page reclaim */
3209 	current->backing_dev_info = inode_to_bdi(inode);
3210 	err = file_remove_privs(file);
3211 	if (err)
3212 		goto out;
3213 
3214 	err = file_update_time(file);
3215 	if (err)
3216 		goto out;
3217 
3218 	if (iocb->ki_flags & IOCB_DIRECT) {
3219 		loff_t pos, endbyte;
3220 
3221 		written = generic_file_direct_write(iocb, from);
3222 		/*
3223 		 * If the write stopped short of completing, fall back to
3224 		 * buffered writes.  Some filesystems do this for writes to
3225 		 * holes, for example.  For DAX files, a buffered write will
3226 		 * not succeed (even if it did, DAX does not handle dirty
3227 		 * page-cache pages correctly).
3228 		 */
3229 		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
3230 			goto out;
3231 
3232 		status = generic_perform_write(file, from, pos = iocb->ki_pos);
3233 		/*
3234 		 * If generic_perform_write() returned a synchronous error
3235 		 * then we want to return the number of bytes which were
3236 		 * direct-written, or the error code if that was zero.  Note
3237 		 * that this differs from normal direct-io semantics, which
3238 		 * will return -EFOO even if some bytes were written.
3239 		 */
3240 		if (unlikely(status < 0)) {
3241 			err = status;
3242 			goto out;
3243 		}
3244 		/*
3245 		 * We need to ensure that the page cache pages are written to
3246 		 * disk and invalidated to preserve the expected O_DIRECT
3247 		 * semantics.
3248 		 */
3249 		endbyte = pos + status - 1;
3250 		err = filemap_write_and_wait_range(mapping, pos, endbyte);
3251 		if (err == 0) {
3252 			iocb->ki_pos = endbyte + 1;
3253 			written += status;
3254 			invalidate_mapping_pages(mapping,
3255 						 pos >> PAGE_SHIFT,
3256 						 endbyte >> PAGE_SHIFT);
3257 		} else {
3258 			/*
3259 			 * We don't know how much we wrote, so just return
3260 			 * the number of bytes which were direct-written
3261 			 */
3262 		}
3263 	} else {
3264 		written = generic_perform_write(file, from, iocb->ki_pos);
3265 		if (likely(written > 0))
3266 			iocb->ki_pos += written;
3267 	}
3268 out:
3269 	current->backing_dev_info = NULL;
3270 	return written ? written : err;
3271 }
3272 EXPORT_SYMBOL(__generic_file_write_iter);
3273 
3274 /**
3275  * generic_file_write_iter - write data to a file
3276  * @iocb:	IO state structure
3277  * @from:	iov_iter with data to write
3278  *
3279  * This is a wrapper around __generic_file_write_iter() to be used by most
3280  * filesystems. It takes care of syncing the file in case of O_SYNC file
3281  * and acquires i_mutex as needed.
3282  */
3283 ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
3284 {
3285 	struct file *file = iocb->ki_filp;
3286 	struct inode *inode = file->f_mapping->host;
3287 	ssize_t ret;
3288 
3289 	inode_lock(inode);
3290 	ret = generic_write_checks(iocb, from);
3291 	if (ret > 0)
3292 		ret = __generic_file_write_iter(iocb, from);
3293 	inode_unlock(inode);
3294 
3295 	if (ret > 0)
3296 		ret = generic_write_sync(iocb, ret);
3297 	return ret;
3298 }
3299 EXPORT_SYMBOL(generic_file_write_iter);
3300 
3301 /**
3302  * try_to_release_page() - release old fs-specific metadata on a page
3303  *
3304  * @page: the page which the kernel is trying to free
3305  * @gfp_mask: memory allocation flags (and I/O mode)
3306  *
3307  * The address_space is to try to release any data against the page
3308  * (presumably at page->private).  If the release was successful, return '1'.
3309  * Otherwise return zero.
3310  *
3311  * This may also be called if PG_fscache is set on a page, indicating that the
3312  * page is known to the local caching routines.
3313  *
3314  * The @gfp_mask argument specifies whether I/O may be performed to release
3315  * this page (__GFP_IO), and whether the call may block (__GFP_RECLAIM & __GFP_FS).
3316  *
3317  */
3318 int try_to_release_page(struct page *page, gfp_t gfp_mask)
3319 {
3320 	struct address_space * const mapping = page->mapping;
3321 
3322 	BUG_ON(!PageLocked(page));
3323 	if (PageWriteback(page))
3324 		return 0;
3325 
3326 	if (mapping && mapping->a_ops->releasepage)
3327 		return mapping->a_ops->releasepage(page, gfp_mask);
3328 	return try_to_free_buffers(page);
3329 }
3330 
3331 EXPORT_SYMBOL(try_to_release_page);
3332