xref: /titanic_51/usr/src/uts/common/vm/page_retire.c (revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 
26 /*
27  * Page Retire - Big Theory Statement.
28  *
29  * This file handles removing sections of faulty memory from use when the
30  * user land FMA Diagnosis Engine requests that a page be removed or when
31  * a CE or UE is detected by the hardware.
32  *
33  * In the bad old days, the kernel side of Page Retire did a lot of the work
34  * on its own. Now, with the DE keeping track of errors, the kernel side is
35  * rather simple minded on most platforms.
36  *
37  * Errors are all reflected to the DE, and after digesting the error and
38  * looking at all previously reported errors, the DE decides what should
39  * be done about the current error. If the DE wants a particular page to
40  * be retired, then the kernel page retire code is invoked via an ioctl.
41  * On non-FMA platforms, the ue_drain and ce_drain paths ends up calling
42  * page retire to handle the error. Since page retire is just a simple
43  * mechanism it doesn't need to differentiate between the different callers.
44  *
45  * The p_toxic field in the page_t is used to indicate which errors have
46  * occurred and what action has been taken on a given page. Because errors are
47  * reported without regard to the locked state of a page, no locks are used
48  * to SET the error bits in p_toxic. However, in order to clear the error
49  * bits, the page_t must be held exclusively locked.
50  *
51  * When page_retire() is called, it must be able to acquire locks, sleep, etc.
52  * It must not be called from high-level interrupt context.
53  *
54  * Depending on how the requested page is being used at the time of the retire
55  * request (and on the availability of sufficient system resources), the page
56  * may be retired immediately, or just marked for retirement later. For
57  * example, locked pages are marked, while free pages are retired. Multiple
58  * requests may be made to retire the same page, although there is no need
59  * to: once the p_toxic flags are set, the page will be retired as soon as it
60  * can be exclusively locked.
61  *
62  * The retire mechanism is driven centrally out of page_unlock(). To expedite
63  * the retirement of pages, further requests for SE_SHARED locks are denied
64  * as long as a page retirement is pending. In addition, as long as pages are
65  * pending retirement a background thread runs periodically trying to retire
66  * those pages. Pages which could not be retired while the system is running
67  * are scrubbed prior to rebooting to avoid latent errors on the next boot.
68  *
69  * UE pages without persistent errors are scrubbed and returned to service.
70  * Recidivist pages, as well as FMA-directed requests for retirement, result
71  * in the page being taken out of service. Once the decision is made to take
72  * a page out of service, the page is cleared, hashed onto the retired_pages
73  * vnode, marked as retired, and it is unlocked.  No other requesters (except
74  * for unretire) are allowed to lock retired pages.
75  *
76  * The public routines return (sadly) 0 if they worked and a non-zero error
77  * value if something went wrong. This is done for the ioctl side of the
78  * world to allow errors to be reflected all the way out to user land. The
79  * non-zero values are explained in comments atop each function.
80  */
81 
82 /*
83  * Things to fix:
84  *
85  * 	1. Trying to retire non-relocatable kvp pages may result in a
86  *      quagmire. This is because seg_kmem() no longer keeps its pages locked,
87  *      and calls page_lookup() in the free path; since kvp pages are modified
88  *      and don't have a usable backing store, page_retire() can't do anything
89  *      with them, and we'll keep denying the lock to seg_kmem_free() in a
90  *      vicious cycle. To prevent that, we don't deny locks to kvp pages, and
91  *      hence only try to retire a page from page_unlock() in the free path.
92  *      Since most kernel pages are indefinitely held anyway, and don't
93  *      participate in I/O, this is of little consequence.
94  *
95  *      2. Low memory situations will be interesting. If we don't have
96  *      enough memory for page_relocate() to succeed, we won't be able to
97  *      retire dirty pages; nobody will be able to push them out to disk
98  *      either, since we aggressively deny the page lock. We could change
99  *      fsflush so it can recognize this situation, grab the lock, and push
100  *      the page out, where we'll catch it in the free path and retire it.
101  *
102  *	3. Beware of places that have code like this in them:
103  *
104  *		if (! page_tryupgrade(pp)) {
105  *			page_unlock(pp);
106  *			while (! page_lock(pp, SE_EXCL, NULL, P_RECLAIM)) {
107  *				/ *NOTHING* /
108  *			}
109  *		}
110  *		page_free(pp);
111  *
112  *	The problem is that pp can change identity right after the
113  *	page_unlock() call.  In particular, page_retire() can step in
114  *	there, change pp's identity, and hash pp onto the retired_vnode.
115  *
116  *	Of course, other functions besides page_retire() can have the
117  *	same effect. A kmem reader can waltz by, set up a mapping to the
118  *	page, and then unlock the page. Page_free() will then go castors
119  *	up. So if anybody is doing this, it's already a bug.
120  *
121  *      4. mdboot()'s call into page_retire_mdboot() should probably be
122  *      moved lower. Where the call is made now, we can get into trouble
123  *      by scrubbing a kernel page that is then accessed later.
124  */
125 
126 #include <sys/types.h>
127 #include <sys/param.h>
128 #include <sys/systm.h>
129 #include <sys/mman.h>
130 #include <sys/vnode.h>
131 #include <sys/vfs_opreg.h>
132 #include <sys/cmn_err.h>
133 #include <sys/ksynch.h>
134 #include <sys/thread.h>
135 #include <sys/disp.h>
136 #include <sys/ontrap.h>
137 #include <sys/vmsystm.h>
138 #include <sys/mem_config.h>
139 #include <sys/atomic.h>
140 #include <sys/callb.h>
141 #include <sys/kobj.h>
142 #include <vm/page.h>
143 #include <vm/vm_dep.h>
144 #include <vm/as.h>
145 #include <vm/hat.h>
146 #include <vm/seg_kmem.h>
147 
148 /*
149  * vnode for all pages which are retired from the VM system;
150  */
151 vnode_t *retired_pages;
152 
153 static int page_retire_pp_finish(page_t *, void *, uint_t);
154 
155 /*
156  * Make a list of all of the pages that have been marked for retirement
157  * but are not yet retired.  At system shutdown, we will scrub all of the
158  * pages in the list in case there are outstanding UEs.  Then, we
159  * cross-check this list against the number of pages that are yet to be
160  * retired, and if we find inconsistencies, we scan every page_t in the
161  * whole system looking for any pages that need to be scrubbed for UEs.
162  * The background thread also uses this queue to determine which pages
163  * it should keep trying to retire.
164  */
165 #ifdef	DEBUG
166 #define	PR_PENDING_QMAX	32
167 #else	/* DEBUG */
168 #define	PR_PENDING_QMAX	256
169 #endif	/* DEBUG */
170 page_t		*pr_pending_q[PR_PENDING_QMAX];
171 kmutex_t	pr_q_mutex;
172 
173 /*
174  * Page retire global kstats
175  */
176 struct page_retire_kstat {
177 	kstat_named_t	pr_retired;
178 	kstat_named_t	pr_requested;
179 	kstat_named_t	pr_requested_free;
180 	kstat_named_t	pr_enqueue_fail;
181 	kstat_named_t	pr_dequeue_fail;
182 	kstat_named_t	pr_pending;
183 	kstat_named_t	pr_pending_kas;
184 	kstat_named_t	pr_failed;
185 	kstat_named_t	pr_failed_kernel;
186 	kstat_named_t	pr_limit;
187 	kstat_named_t	pr_limit_exceeded;
188 	kstat_named_t	pr_fma;
189 	kstat_named_t	pr_mce;
190 	kstat_named_t	pr_ue;
191 	kstat_named_t	pr_ue_cleared_retire;
192 	kstat_named_t	pr_ue_cleared_free;
193 	kstat_named_t	pr_ue_persistent;
194 	kstat_named_t	pr_unretired;
195 };
196 
197 static struct page_retire_kstat page_retire_kstat = {
198 	{ "pages_retired",		KSTAT_DATA_UINT64},
199 	{ "pages_retire_request",	KSTAT_DATA_UINT64},
200 	{ "pages_retire_request_free",	KSTAT_DATA_UINT64},
201 	{ "pages_notenqueued", 		KSTAT_DATA_UINT64},
202 	{ "pages_notdequeued", 		KSTAT_DATA_UINT64},
203 	{ "pages_pending", 		KSTAT_DATA_UINT64},
204 	{ "pages_pending_kas", 		KSTAT_DATA_UINT64},
205 	{ "pages_deferred",		KSTAT_DATA_UINT64},
206 	{ "pages_deferred_kernel",	KSTAT_DATA_UINT64},
207 	{ "pages_limit",		KSTAT_DATA_UINT64},
208 	{ "pages_limit_exceeded",	KSTAT_DATA_UINT64},
209 	{ "pages_fma",			KSTAT_DATA_UINT64},
210 	{ "pages_multiple_ce",		KSTAT_DATA_UINT64},
211 	{ "pages_ue",			KSTAT_DATA_UINT64},
212 	{ "pages_ue_cleared_retired",	KSTAT_DATA_UINT64},
213 	{ "pages_ue_cleared_freed",	KSTAT_DATA_UINT64},
214 	{ "pages_ue_persistent",	KSTAT_DATA_UINT64},
215 	{ "pages_unretired",		KSTAT_DATA_UINT64},
216 };
217 
218 static kstat_t  *page_retire_ksp = NULL;
219 
220 #define	PR_INCR_KSTAT(stat)	\
221 	atomic_inc_64(&(page_retire_kstat.stat.value.ui64))
222 #define	PR_DECR_KSTAT(stat)	\
223 	atomic_dec_64(&(page_retire_kstat.stat.value.ui64))
224 
225 #define	PR_KSTAT_RETIRED_CE	(page_retire_kstat.pr_mce.value.ui64)
226 #define	PR_KSTAT_RETIRED_FMA	(page_retire_kstat.pr_fma.value.ui64)
227 #define	PR_KSTAT_RETIRED_NOTUE	(PR_KSTAT_RETIRED_CE + PR_KSTAT_RETIRED_FMA)
228 #define	PR_KSTAT_PENDING	(page_retire_kstat.pr_pending.value.ui64)
229 #define	PR_KSTAT_PENDING_KAS	(page_retire_kstat.pr_pending_kas.value.ui64)
230 #define	PR_KSTAT_EQFAIL		(page_retire_kstat.pr_enqueue_fail.value.ui64)
231 #define	PR_KSTAT_DQFAIL		(page_retire_kstat.pr_dequeue_fail.value.ui64)
232 
233 /*
234  * page retire kstats to list all retired pages
235  */
236 static int pr_list_kstat_update(kstat_t *ksp, int rw);
237 static int pr_list_kstat_snapshot(kstat_t *ksp, void *buf, int rw);
238 kmutex_t pr_list_kstat_mutex;
239 
240 /*
241  * Limit the number of multiple CE page retires.
242  * The default is 0.1% of physmem, or 1 in 1000 pages. This is set in
243  * basis points, where 100 basis points equals one percent.
244  */
245 #define	MCE_BPT	10
246 uint64_t	max_pages_retired_bps = MCE_BPT;
247 #define	PAGE_RETIRE_LIMIT	((physmem * max_pages_retired_bps) / 10000)
248 
249 /*
250  * Control over the verbosity of page retirement.
251  *
252  * When set to zero (the default), no messages will be printed.
253  * When set to one, summary messages will be printed.
254  * When set > one, all messages will be printed.
255  *
256  * A value of one will trigger detailed messages for retirement operations,
257  * and is intended as a platform tunable for processors where FMA's DE does
258  * not run (e.g., spitfire). Values > one are intended for debugging only.
259  */
260 int page_retire_messages = 0;
261 
262 /*
263  * Control whether or not we return scrubbed UE pages to service.
264  * By default we do not since FMA wants to run its diagnostics first
265  * and then ask us to unretire the page if it passes. Non-FMA platforms
266  * may set this to zero so we will only retire recidivist pages. It should
267  * not be changed by the user.
268  */
269 int page_retire_first_ue = 1;
270 
271 /*
272  * Master enable for page retire. This prevents a CE or UE early in boot
273  * from trying to retire a page before page_retire_init() has finished
274  * setting things up. This is internal only and is not a tunable!
275  */
276 static int pr_enable = 0;
277 
278 static void (*memscrub_notify_func)(uint64_t);
279 
280 #ifdef	DEBUG
281 struct page_retire_debug {
282 	int prd_dup1;
283 	int prd_dup2;
284 	int prd_qdup;
285 	int prd_noaction;
286 	int prd_queued;
287 	int prd_notqueued;
288 	int prd_dequeue;
289 	int prd_top;
290 	int prd_locked;
291 	int prd_reloc;
292 	int prd_relocfail;
293 	int prd_mod;
294 	int prd_mod_late;
295 	int prd_kern;
296 	int prd_free;
297 	int prd_noreclaim;
298 	int prd_hashout;
299 	int prd_fma;
300 	int prd_uescrubbed;
301 	int prd_uenotscrubbed;
302 	int prd_mce;
303 	int prd_prlocked;
304 	int prd_prnotlocked;
305 	int prd_prretired;
306 	int prd_ulocked;
307 	int prd_unotretired;
308 	int prd_udestroy;
309 	int prd_uhashout;
310 	int prd_uunretired;
311 	int prd_unotlocked;
312 	int prd_checkhit;
313 	int prd_checkmiss_pend;
314 	int prd_checkmiss_noerr;
315 	int prd_tctop;
316 	int prd_tclocked;
317 	int prd_hunt;
318 	int prd_dohunt;
319 	int prd_earlyhunt;
320 	int prd_latehunt;
321 	int prd_nofreedemote;
322 	int prd_nodemote;
323 	int prd_demoted;
324 } pr_debug;
325 
326 #define	PR_DEBUG(foo)	((pr_debug.foo)++)
327 
328 /*
329  * A type histogram. We record the incidence of the various toxic
330  * flag combinations along with the interesting page attributes. The
331  * goal is to get as many combinations as we can while driving all
332  * pr_debug values nonzero (indicating we've exercised all possible
333  * code paths across all possible page types). Not all combinations
334  * will make sense -- e.g. PRT_MOD|PRT_KERNEL.
335  *
336  * pr_type offset bit encoding (when examining with a debugger):
337  *
338  *    PRT_NAMED  - 0x4
339  *    PRT_KERNEL - 0x8
340  *    PRT_FREE   - 0x10
341  *    PRT_MOD    - 0x20
342  *    PRT_FMA    - 0x0
343  *    PRT_MCE    - 0x40
344  *    PRT_UE     - 0x80
345  */
346 
347 #define	PRT_NAMED	0x01
348 #define	PRT_KERNEL	0x02
349 #define	PRT_FREE	0x04
350 #define	PRT_MOD		0x08
351 #define	PRT_FMA		0x00	/* yes, this is not a mistake */
352 #define	PRT_MCE		0x10
353 #define	PRT_UE		0x20
354 #define	PRT_ALL		0x3F
355 
356 int pr_types[PRT_ALL+1];
357 
358 #define	PR_TYPES(pp)	{			\
359 	int whichtype = 0;			\
360 	if (pp->p_vnode)			\
361 		whichtype |= PRT_NAMED;		\
362 	if (PP_ISKAS(pp))			\
363 		whichtype |= PRT_KERNEL;	\
364 	if (PP_ISFREE(pp))			\
365 		whichtype |= PRT_FREE;		\
366 	if (hat_ismod(pp))			\
367 		whichtype |= PRT_MOD;		\
368 	if (pp->p_toxic & PR_UE)		\
369 		whichtype |= PRT_UE;		\
370 	if (pp->p_toxic & PR_MCE)		\
371 		whichtype |= PRT_MCE;		\
372 	pr_types[whichtype]++;			\
373 }
374 
375 int recl_calls;
376 int recl_mtbf = 3;
377 int reloc_calls;
378 int reloc_mtbf = 7;
379 int pr_calls;
380 int pr_mtbf = 15;
381 
382 #define	MTBF(v, f)	(((++(v)) & (f)) != (f))
383 
384 #else	/* DEBUG */
385 
386 #define	PR_DEBUG(foo)	/* nothing */
387 #define	PR_TYPES(foo)	/* nothing */
388 #define	MTBF(v, f)	(1)
389 
390 #endif	/* DEBUG */
391 
392 /*
393  * page_retire_done() - completion processing
394  *
395  * Used by the page_retire code for common completion processing.
396  * It keeps track of how many times a given result has happened,
397  * and writes out an occasional message.
398  *
399  * May be called with a NULL pp (PRD_INVALID_PA case).
400  */
401 #define	PRD_INVALID_KEY		-1
402 #define	PRD_SUCCESS		0
403 #define	PRD_PENDING		1
404 #define	PRD_FAILED		2
405 #define	PRD_DUPLICATE		3
406 #define	PRD_INVALID_PA		4
407 #define	PRD_LIMIT		5
408 #define	PRD_UE_SCRUBBED		6
409 #define	PRD_UNR_SUCCESS		7
410 #define	PRD_UNR_CANTLOCK	8
411 #define	PRD_UNR_NOT		9
412 
413 typedef struct page_retire_op {
414 	int	pr_key;		/* one of the PRD_* defines from above */
415 	int	pr_count;	/* How many times this has happened */
416 	int	pr_retval;	/* return value */
417 	int	pr_msglvl;	/* message level - when to print */
418 	char	*pr_message;	/* Cryptic message for field service */
419 } page_retire_op_t;
420 
421 static page_retire_op_t page_retire_ops[] = {
422 	/* key			count	retval	msglvl	message */
423 	{PRD_SUCCESS,		0,	0,	1,
424 		"Page 0x%08x.%08x removed from service"},
425 	{PRD_PENDING,		0,	EAGAIN,	2,
426 		"Page 0x%08x.%08x will be retired on free"},
427 	{PRD_FAILED,		0,	EAGAIN,	0, NULL},
428 	{PRD_DUPLICATE,		0,	EIO,	2,
429 		"Page 0x%08x.%08x already retired or pending"},
430 	{PRD_INVALID_PA,	0,	EINVAL, 2,
431 		"PA 0x%08x.%08x is not a relocatable page"},
432 	{PRD_LIMIT,		0,	0,	1,
433 		"Page 0x%08x.%08x not retired due to limit exceeded"},
434 	{PRD_UE_SCRUBBED,	0,	0,	1,
435 		"Previously reported error on page 0x%08x.%08x cleared"},
436 	{PRD_UNR_SUCCESS,	0,	0,	1,
437 		"Page 0x%08x.%08x returned to service"},
438 	{PRD_UNR_CANTLOCK,	0,	EAGAIN,	2,
439 		"Page 0x%08x.%08x could not be unretired"},
440 	{PRD_UNR_NOT,		0,	EIO,	2,
441 		"Page 0x%08x.%08x is not retired"},
442 	{PRD_INVALID_KEY,	0,	0,	0, NULL} /* MUST BE LAST! */
443 };
444 
445 /*
446  * print a message if page_retire_messages is true.
447  */
448 #define	PR_MESSAGE(debuglvl, msglvl, msg, pa)				\
449 {									\
450 	uint64_t p = (uint64_t)pa;					\
451 	if (page_retire_messages >= msglvl && msg != NULL) {		\
452 		cmn_err(debuglvl, msg,					\
453 		    (uint32_t)(p >> 32), (uint32_t)p);			\
454 	}								\
455 }
456 
457 /*
458  * Note that multiple bits may be set in a single settoxic operation.
459  * May be called without the page locked.
460  */
461 void
462 page_settoxic(page_t *pp, uchar_t bits)
463 {
464 	atomic_or_8(&pp->p_toxic, bits);
465 }
466 
467 /*
468  * Note that multiple bits may cleared in a single clrtoxic operation.
469  * Must be called with the page exclusively locked to prevent races which
470  * may attempt to retire a page without any toxic bits set.
471  * Note that the PR_CAPTURE bit can be cleared without the exclusive lock
472  * being held as there is a separate mutex which protects that bit.
473  */
474 void
475 page_clrtoxic(page_t *pp, uchar_t bits)
476 {
477 	ASSERT((bits & PR_CAPTURE) || PAGE_EXCL(pp));
478 	atomic_and_8(&pp->p_toxic, ~bits);
479 }
480 
481 /*
482  * Prints any page retire messages to the user, and decides what
483  * error code is appropriate for the condition reported.
484  */
485 static int
486 page_retire_done(page_t *pp, int code)
487 {
488 	page_retire_op_t *prop;
489 	uint64_t	pa = 0;
490 	int		i;
491 
492 	if (pp != NULL) {
493 		pa = mmu_ptob((uint64_t)pp->p_pagenum);
494 	}
495 
496 	prop = NULL;
497 	for (i = 0; page_retire_ops[i].pr_key != PRD_INVALID_KEY; i++) {
498 		if (page_retire_ops[i].pr_key == code) {
499 			prop = &page_retire_ops[i];
500 			break;
501 		}
502 	}
503 
504 #ifdef	DEBUG
505 	if (page_retire_ops[i].pr_key == PRD_INVALID_KEY) {
506 		cmn_err(CE_PANIC, "page_retire_done: Invalid opcode %d", code);
507 	}
508 #endif
509 
510 	ASSERT(prop->pr_key == code);
511 
512 	prop->pr_count++;
513 
514 	PR_MESSAGE(CE_NOTE, prop->pr_msglvl, prop->pr_message, pa);
515 	if (pp != NULL) {
516 		page_settoxic(pp, PR_MSG);
517 	}
518 
519 	return (prop->pr_retval);
520 }
521 
522 /*
523  * Act like page_destroy(), but instead of freeing the page, hash it onto
524  * the retired_pages vnode, and mark it retired.
525  *
526  * For fun, we try to scrub the page until it's squeaky clean.
527  * availrmem is adjusted here.
528  */
529 static void
530 page_retire_destroy(page_t *pp)
531 {
532 	u_offset_t off = (u_offset_t)((uintptr_t)pp);
533 
534 	ASSERT(PAGE_EXCL(pp));
535 	ASSERT(!PP_ISFREE(pp));
536 	ASSERT(pp->p_szc == 0);
537 	ASSERT(!hat_page_is_mapped(pp));
538 	ASSERT(!pp->p_vnode);
539 
540 	page_clr_all_props(pp);
541 	pagescrub(pp, 0, MMU_PAGESIZE);
542 
543 	pp->p_next = NULL;
544 	pp->p_prev = NULL;
545 	if (page_hashin(pp, retired_pages, off, NULL) == 0) {
546 		cmn_err(CE_PANIC, "retired page %p hashin failed", (void *)pp);
547 	}
548 
549 	page_settoxic(pp, PR_RETIRED);
550 	PR_INCR_KSTAT(pr_retired);
551 
552 	if (pp->p_toxic & PR_FMA) {
553 		PR_INCR_KSTAT(pr_fma);
554 	} else if (pp->p_toxic & PR_UE) {
555 		PR_INCR_KSTAT(pr_ue);
556 	} else {
557 		PR_INCR_KSTAT(pr_mce);
558 	}
559 
560 	mutex_enter(&freemem_lock);
561 	availrmem--;
562 	mutex_exit(&freemem_lock);
563 
564 	page_unlock(pp);
565 }
566 
567 /*
568  * Check whether the number of pages which have been retired already exceeds
569  * the maximum allowable percentage of memory which may be retired.
570  *
571  * Returns 1 if the limit has been exceeded.
572  */
573 static int
574 page_retire_limit(void)
575 {
576 	if (PR_KSTAT_RETIRED_NOTUE >= (uint64_t)PAGE_RETIRE_LIMIT) {
577 		PR_INCR_KSTAT(pr_limit_exceeded);
578 		return (1);
579 	}
580 
581 	return (0);
582 }
583 
584 #define	MSG_DM	"Data Mismatch occurred at PA 0x%08x.%08x"		\
585 	"[ 0x%x != 0x%x ] while attempting to clear previously "	\
586 	"reported error; page removed from service"
587 
588 #define	MSG_UE	"Uncorrectable Error occurred at PA 0x%08x.%08x while "	\
589 	"attempting to clear previously reported error; page removed "	\
590 	"from service"
591 
592 /*
593  * Attempt to clear a UE from a page.
594  * Returns 1 if the error has been successfully cleared.
595  */
596 static int
597 page_clear_transient_ue(page_t *pp)
598 {
599 	caddr_t		kaddr;
600 	uint8_t		rb, wb;
601 	uint64_t	pa;
602 	uint32_t	pa_hi, pa_lo;
603 	on_trap_data_t	otd;
604 	int		errors = 0;
605 	int		i;
606 
607 	ASSERT(PAGE_EXCL(pp));
608 	ASSERT(PP_PR_REQ(pp));
609 	ASSERT(pp->p_szc == 0);
610 	ASSERT(!hat_page_is_mapped(pp));
611 
612 	/*
613 	 * Clear the page and attempt to clear the UE.  If we trap
614 	 * on the next access to the page, we know the UE has recurred.
615 	 */
616 	pagescrub(pp, 0, PAGESIZE);
617 
618 	/*
619 	 * Map the page and write a bunch of bit patterns to compare
620 	 * what we wrote with what we read back.  This isn't a perfect
621 	 * test but it should be good enough to catch most of the
622 	 * recurring UEs. If this fails to catch a recurrent UE, we'll
623 	 * retire the page the next time we see a UE on the page.
624 	 */
625 	kaddr = ppmapin(pp, PROT_READ|PROT_WRITE, (caddr_t)-1);
626 
627 	pa = ptob((uint64_t)page_pptonum(pp));
628 	pa_hi = (uint32_t)(pa >> 32);
629 	pa_lo = (uint32_t)pa;
630 
631 	/*
632 	 * Disable preemption to prevent the off chance that
633 	 * we migrate while in the middle of running through
634 	 * the bit pattern and run on a different processor
635 	 * than what we started on.
636 	 */
637 	kpreempt_disable();
638 
639 	/*
640 	 * Fill the page with each (0x00 - 0xFF] bit pattern, flushing
641 	 * the cache in between reading and writing.  We do this under
642 	 * on_trap() protection to avoid recursion.
643 	 */
644 	if (on_trap(&otd, OT_DATA_EC)) {
645 		PR_MESSAGE(CE_WARN, 1, MSG_UE, pa);
646 		errors = 1;
647 	} else {
648 		for (wb = 0xff; wb > 0; wb--) {
649 			for (i = 0; i < PAGESIZE; i++) {
650 				kaddr[i] = wb;
651 			}
652 
653 			sync_data_memory(kaddr, PAGESIZE);
654 
655 			for (i = 0; i < PAGESIZE; i++) {
656 				rb = kaddr[i];
657 				if (rb != wb) {
658 					/*
659 					 * We had a mismatch without a trap.
660 					 * Uh-oh. Something is really wrong
661 					 * with this system.
662 					 */
663 					if (page_retire_messages) {
664 						cmn_err(CE_WARN, MSG_DM,
665 						    pa_hi, pa_lo, rb, wb);
666 					}
667 					errors = 1;
668 					goto out;	/* double break */
669 				}
670 			}
671 		}
672 	}
673 out:
674 	no_trap();
675 	kpreempt_enable();
676 	ppmapout(kaddr);
677 
678 	return (errors ? 0 : 1);
679 }
680 
681 /*
682  * Try to clear a page_t with a single UE. If the UE was transient, it is
683  * returned to service, and we return 1. Otherwise we return 0 meaning
684  * that further processing is required to retire the page.
685  */
686 static int
687 page_retire_transient_ue(page_t *pp)
688 {
689 	ASSERT(PAGE_EXCL(pp));
690 	ASSERT(!hat_page_is_mapped(pp));
691 
692 	/*
693 	 * If this page is a repeat offender, retire him under the
694 	 * "two strikes and you're out" rule. The caller is responsible
695 	 * for scrubbing the page to try to clear the error.
696 	 */
697 	if (pp->p_toxic & PR_UE_SCRUBBED) {
698 		PR_INCR_KSTAT(pr_ue_persistent);
699 		return (0);
700 	}
701 
702 	if (page_clear_transient_ue(pp)) {
703 		/*
704 		 * We set the PR_SCRUBBED_UE bit; if we ever see this
705 		 * page again, we will retire it, no questions asked.
706 		 */
707 		page_settoxic(pp, PR_UE_SCRUBBED);
708 
709 		if (page_retire_first_ue) {
710 			PR_INCR_KSTAT(pr_ue_cleared_retire);
711 			return (0);
712 		} else {
713 			PR_INCR_KSTAT(pr_ue_cleared_free);
714 
715 			page_clrtoxic(pp, PR_UE | PR_MCE | PR_MSG);
716 
717 			/* LINTED: CONSTCOND */
718 			VN_DISPOSE(pp, B_FREE, 1, kcred);
719 			return (1);
720 		}
721 	}
722 
723 	PR_INCR_KSTAT(pr_ue_persistent);
724 	return (0);
725 }
726 
727 /*
728  * Update the statistics dynamically when our kstat is read.
729  */
730 static int
731 page_retire_kstat_update(kstat_t *ksp, int rw)
732 {
733 	struct page_retire_kstat *pr;
734 
735 	if (ksp == NULL)
736 		return (EINVAL);
737 
738 	switch (rw) {
739 
740 	case KSTAT_READ:
741 		pr = (struct page_retire_kstat *)ksp->ks_data;
742 		ASSERT(pr == &page_retire_kstat);
743 		pr->pr_limit.value.ui64 = PAGE_RETIRE_LIMIT;
744 		return (0);
745 
746 	case KSTAT_WRITE:
747 		return (EACCES);
748 
749 	default:
750 		return (EINVAL);
751 	}
752 	/*NOTREACHED*/
753 }
754 
755 static int
756 pr_list_kstat_update(kstat_t *ksp, int rw)
757 {
758 	uint_t count;
759 	page_t *pp;
760 	kmutex_t *vphm;
761 
762 	if (rw == KSTAT_WRITE)
763 		return (EACCES);
764 
765 	vphm = page_vnode_mutex(retired_pages);
766 	mutex_enter(vphm);
767 	/* Needs to be under a lock so that for loop will work right */
768 	if (retired_pages->v_pages == NULL) {
769 		mutex_exit(vphm);
770 		ksp->ks_ndata = 0;
771 		ksp->ks_data_size = 0;
772 		return (0);
773 	}
774 
775 	count = 1;
776 	for (pp = retired_pages->v_pages->p_vpnext;
777 	    pp != retired_pages->v_pages; pp = pp->p_vpnext) {
778 		count++;
779 	}
780 	mutex_exit(vphm);
781 
782 	ksp->ks_ndata = count;
783 	ksp->ks_data_size = count * 2 * sizeof (uint64_t);
784 
785 	return (0);
786 }
787 
788 /*
789  * all spans will be pagesize and no coalescing will be done with the
790  * list produced.
791  */
792 static int
793 pr_list_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
794 {
795 	kmutex_t *vphm;
796 	page_t *pp;
797 	struct memunit {
798 		uint64_t address;
799 		uint64_t size;
800 	} *kspmem;
801 
802 	if (rw == KSTAT_WRITE)
803 		return (EACCES);
804 
805 	ksp->ks_snaptime = gethrtime();
806 
807 	kspmem = (struct memunit *)buf;
808 
809 	vphm = page_vnode_mutex(retired_pages);
810 	mutex_enter(vphm);
811 	pp = retired_pages->v_pages;
812 	if (((caddr_t)kspmem >= (caddr_t)buf + ksp->ks_data_size) ||
813 	    (pp == NULL)) {
814 		mutex_exit(vphm);
815 		return (0);
816 	}
817 	kspmem->address = ptob(pp->p_pagenum);
818 	kspmem->size = PAGESIZE;
819 	kspmem++;
820 	for (pp = pp->p_vpnext; pp != retired_pages->v_pages;
821 	    pp = pp->p_vpnext, kspmem++) {
822 		if ((caddr_t)kspmem >= (caddr_t)buf + ksp->ks_data_size)
823 			break;
824 		kspmem->address = ptob(pp->p_pagenum);
825 		kspmem->size = PAGESIZE;
826 	}
827 	mutex_exit(vphm);
828 
829 	return (0);
830 }
831 
832 /*
833  * page_retire_pend_count -- helper function for page_capture_thread,
834  * returns the number of pages pending retirement.
835  */
836 uint64_t
837 page_retire_pend_count(void)
838 {
839 	return (PR_KSTAT_PENDING);
840 }
841 
842 uint64_t
843 page_retire_pend_kas_count(void)
844 {
845 	return (PR_KSTAT_PENDING_KAS);
846 }
847 
848 void
849 page_retire_incr_pend_count(void *datap)
850 {
851 	PR_INCR_KSTAT(pr_pending);
852 
853 	if ((datap == &kvp) || (datap == &zvp)) {
854 		PR_INCR_KSTAT(pr_pending_kas);
855 	}
856 }
857 
858 void
859 page_retire_decr_pend_count(void *datap)
860 {
861 	PR_DECR_KSTAT(pr_pending);
862 
863 	if ((datap == &kvp) || (datap == &zvp)) {
864 		PR_DECR_KSTAT(pr_pending_kas);
865 	}
866 }
867 
868 /*
869  * Initialize the page retire mechanism:
870  *
871  *   - Establish the correctable error retire limit.
872  *   - Initialize locks.
873  *   - Build the retired_pages vnode.
874  *   - Set up the kstats.
875  *   - Fire off the background thread.
876  *   - Tell page_retire() it's OK to start retiring pages.
877  */
878 void
879 page_retire_init(void)
880 {
881 	const fs_operation_def_t retired_vnodeops_template[] = {
882 		{ NULL, NULL }
883 	};
884 	struct vnodeops *vops;
885 	kstat_t *ksp;
886 
887 	const uint_t page_retire_ndata =
888 	    sizeof (page_retire_kstat) / sizeof (kstat_named_t);
889 
890 	ASSERT(page_retire_ksp == NULL);
891 
892 	if (max_pages_retired_bps <= 0) {
893 		max_pages_retired_bps = MCE_BPT;
894 	}
895 
896 	mutex_init(&pr_q_mutex, NULL, MUTEX_DEFAULT, NULL);
897 
898 	retired_pages = vn_alloc(KM_SLEEP);
899 	if (vn_make_ops("retired_pages", retired_vnodeops_template, &vops)) {
900 		cmn_err(CE_PANIC,
901 		    "page_retired_init: can't make retired vnodeops");
902 	}
903 	vn_setops(retired_pages, vops);
904 
905 	if ((page_retire_ksp = kstat_create("unix", 0, "page_retire",
906 	    "misc", KSTAT_TYPE_NAMED, page_retire_ndata,
907 	    KSTAT_FLAG_VIRTUAL)) == NULL) {
908 		cmn_err(CE_WARN, "kstat_create for page_retire failed");
909 	} else {
910 		page_retire_ksp->ks_data = (void *)&page_retire_kstat;
911 		page_retire_ksp->ks_update = page_retire_kstat_update;
912 		kstat_install(page_retire_ksp);
913 	}
914 
915 	mutex_init(&pr_list_kstat_mutex, NULL, MUTEX_DEFAULT, NULL);
916 	ksp = kstat_create("unix", 0, "page_retire_list", "misc",
917 	    KSTAT_TYPE_RAW, 0, KSTAT_FLAG_VAR_SIZE | KSTAT_FLAG_VIRTUAL);
918 	if (ksp != NULL) {
919 		ksp->ks_update = pr_list_kstat_update;
920 		ksp->ks_snapshot = pr_list_kstat_snapshot;
921 		ksp->ks_lock = &pr_list_kstat_mutex;
922 		kstat_install(ksp);
923 	}
924 
925 	memscrub_notify_func =
926 	    (void(*)(uint64_t))kobj_getsymvalue("memscrub_notify", 0);
927 
928 	page_capture_register_callback(PC_RETIRE, -1, page_retire_pp_finish);
929 	pr_enable = 1;
930 }
931 
932 /*
933  * page_retire_hunt() callback for the retire thread.
934  */
935 static void
936 page_retire_thread_cb(page_t *pp)
937 {
938 	PR_DEBUG(prd_tctop);
939 	if (!PP_ISKAS(pp) && page_trylock(pp, SE_EXCL)) {
940 		PR_DEBUG(prd_tclocked);
941 		page_unlock(pp);
942 	}
943 }
944 
945 /*
946  * Callback used by page_trycapture() to finish off retiring a page.
947  * The page has already been cleaned and we've been given sole access to
948  * it.
949  * Always returns 0 to indicate that callback succeded as the callback never
950  * fails to finish retiring the given page.
951  */
952 /*ARGSUSED*/
953 static int
954 page_retire_pp_finish(page_t *pp, void *notused, uint_t flags)
955 {
956 	int		toxic;
957 
958 	ASSERT(PAGE_EXCL(pp));
959 	ASSERT(pp->p_iolock_state == 0);
960 	ASSERT(pp->p_szc == 0);
961 
962 	toxic = pp->p_toxic;
963 
964 	/*
965 	 * The problem page is locked, demoted, unmapped, not free,
966 	 * hashed out, and not COW or mlocked (whew!).
967 	 *
968 	 * Now we select our ammunition, take it around back, and shoot it.
969 	 */
970 	if (toxic & PR_UE) {
971 ue_error:
972 		if (page_retire_transient_ue(pp)) {
973 			PR_DEBUG(prd_uescrubbed);
974 			(void) page_retire_done(pp, PRD_UE_SCRUBBED);
975 		} else {
976 			PR_DEBUG(prd_uenotscrubbed);
977 			page_retire_destroy(pp);
978 			(void) page_retire_done(pp, PRD_SUCCESS);
979 		}
980 		return (0);
981 	} else if (toxic & PR_FMA) {
982 		PR_DEBUG(prd_fma);
983 		page_retire_destroy(pp);
984 		(void) page_retire_done(pp, PRD_SUCCESS);
985 		return (0);
986 	} else if (toxic & PR_MCE) {
987 		PR_DEBUG(prd_mce);
988 		page_retire_destroy(pp);
989 		(void) page_retire_done(pp, PRD_SUCCESS);
990 		return (0);
991 	}
992 
993 	/*
994 	 * When page_retire_first_ue is set to zero and a UE occurs which is
995 	 * transient, it's possible that we clear some flags set by a second
996 	 * UE error on the page which occurs while the first is currently being
997 	 * handled and thus we need to handle the case where none of the above
998 	 * are set.  In this instance, PR_UE_SCRUBBED should be set and thus
999 	 * we should execute the UE code above.
1000 	 */
1001 	if (toxic & PR_UE_SCRUBBED) {
1002 		goto ue_error;
1003 	}
1004 
1005 	/*
1006 	 * It's impossible to get here.
1007 	 */
1008 	panic("bad toxic flags 0x%x in page_retire_pp_finish\n", toxic);
1009 	return (0);
1010 }
1011 
1012 /*
1013  * page_retire() - the front door in to retire a page.
1014  *
1015  * Ideally, page_retire() would instantly retire the requested page.
1016  * Unfortunately, some pages are locked or otherwise tied up and cannot be
1017  * retired right away.  We use the page capture logic to deal with this
1018  * situation as it will continuously try to retire the page in the background
1019  * if the first attempt fails.  Success is determined by looking to see whether
1020  * the page has been retired after the page_trycapture() attempt.
1021  *
1022  * Returns:
1023  *
1024  *   - 0 on success,
1025  *   - EINVAL when the PA is whacko,
1026  *   - EIO if the page is already retired or already pending retirement, or
1027  *   - EAGAIN if the page could not be _immediately_ retired but is pending.
1028  */
1029 int
1030 page_retire(uint64_t pa, uchar_t reason)
1031 {
1032 	page_t	*pp;
1033 
1034 	ASSERT(reason & PR_REASONS);		/* there must be a reason */
1035 	ASSERT(!(reason & ~PR_REASONS));	/* but no other bits */
1036 
1037 	pp = page_numtopp_nolock(mmu_btop(pa));
1038 	if (pp == NULL) {
1039 		PR_MESSAGE(CE_WARN, 1, "Cannot schedule clearing of error on"
1040 		    " page 0x%08x.%08x; page is not relocatable memory", pa);
1041 		return (page_retire_done(pp, PRD_INVALID_PA));
1042 	}
1043 	if (PP_RETIRED(pp)) {
1044 		PR_DEBUG(prd_dup1);
1045 		return (page_retire_done(pp, PRD_DUPLICATE));
1046 	}
1047 
1048 	if (memscrub_notify_func != NULL) {
1049 		(void) memscrub_notify_func(pa);
1050 	}
1051 
1052 	if ((reason & PR_UE) && !PP_TOXIC(pp)) {
1053 		PR_MESSAGE(CE_NOTE, 1, "Scheduling clearing of error on"
1054 		    " page 0x%08x.%08x", pa);
1055 	} else if (PP_PR_REQ(pp)) {
1056 		PR_DEBUG(prd_dup2);
1057 		return (page_retire_done(pp, PRD_DUPLICATE));
1058 	} else {
1059 		PR_MESSAGE(CE_NOTE, 1, "Scheduling removal of"
1060 		    " page 0x%08x.%08x", pa);
1061 	}
1062 
1063 	/* Avoid setting toxic bits in the first place */
1064 	if ((reason & (PR_FMA | PR_MCE)) && !(reason & PR_UE) &&
1065 	    page_retire_limit()) {
1066 		return (page_retire_done(pp, PRD_LIMIT));
1067 	}
1068 
1069 	if (MTBF(pr_calls, pr_mtbf)) {
1070 		page_settoxic(pp, reason);
1071 		if (page_trycapture(pp, 0, CAPTURE_RETIRE, pp->p_vnode) == 0) {
1072 			PR_DEBUG(prd_prlocked);
1073 		} else {
1074 			PR_DEBUG(prd_prnotlocked);
1075 		}
1076 	} else {
1077 		PR_DEBUG(prd_prnotlocked);
1078 	}
1079 
1080 	if (PP_RETIRED(pp)) {
1081 		PR_DEBUG(prd_prretired);
1082 		return (0);
1083 	} else {
1084 		cv_signal(&pc_cv);
1085 		PR_INCR_KSTAT(pr_failed);
1086 
1087 		if (pp->p_toxic & PR_MSG) {
1088 			return (page_retire_done(pp, PRD_FAILED));
1089 		} else {
1090 			return (page_retire_done(pp, PRD_PENDING));
1091 		}
1092 	}
1093 }
1094 
1095 /*
1096  * Take a retired page off the retired-pages vnode and clear the toxic flags.
1097  * If "free" is nonzero, lock it and put it back on the freelist. If "free"
1098  * is zero, the caller already holds SE_EXCL lock so we simply unretire it
1099  * and don't do anything else with it.
1100  *
1101  * Any unretire messages are printed from this routine.
1102  *
1103  * Returns 0 if page pp was unretired; else an error code.
1104  *
1105  * If flags is:
1106  *	PR_UNR_FREE - lock the page, clear the toxic flags and free it
1107  *	    to the freelist.
1108  *	PR_UNR_TEMP - lock the page, unretire it, leave the toxic
1109  *	    bits set as is and return it to the caller.
1110  *	PR_UNR_CLEAN - page is SE_EXCL locked, unretire it, clear the
1111  *	    toxic flags and return it to caller as is.
1112  */
1113 int
1114 page_unretire_pp(page_t *pp, int flags)
1115 {
1116 	/*
1117 	 * To be retired, a page has to be hashed onto the retired_pages vnode
1118 	 * and have PR_RETIRED set in p_toxic.
1119 	 */
1120 	if (flags == PR_UNR_CLEAN ||
1121 	    page_try_reclaim_lock(pp, SE_EXCL, SE_RETIRED)) {
1122 		ASSERT(PAGE_EXCL(pp));
1123 		PR_DEBUG(prd_ulocked);
1124 		if (!PP_RETIRED(pp)) {
1125 			PR_DEBUG(prd_unotretired);
1126 			page_unlock(pp);
1127 			return (page_retire_done(pp, PRD_UNR_NOT));
1128 		}
1129 
1130 		PR_MESSAGE(CE_NOTE, 1, "unretiring retired"
1131 		    " page 0x%08x.%08x", mmu_ptob((uint64_t)pp->p_pagenum));
1132 		if (pp->p_toxic & PR_FMA) {
1133 			PR_DECR_KSTAT(pr_fma);
1134 		} else if (pp->p_toxic & PR_UE) {
1135 			PR_DECR_KSTAT(pr_ue);
1136 		} else {
1137 			PR_DECR_KSTAT(pr_mce);
1138 		}
1139 
1140 		if (flags == PR_UNR_TEMP)
1141 			page_clrtoxic(pp, PR_RETIRED);
1142 		else
1143 			page_clrtoxic(pp, PR_TOXICFLAGS);
1144 
1145 		if (flags == PR_UNR_FREE) {
1146 			PR_DEBUG(prd_udestroy);
1147 			page_destroy(pp, 0);
1148 		} else {
1149 			PR_DEBUG(prd_uhashout);
1150 			page_hashout(pp, NULL);
1151 		}
1152 
1153 		mutex_enter(&freemem_lock);
1154 		availrmem++;
1155 		mutex_exit(&freemem_lock);
1156 
1157 		PR_DEBUG(prd_uunretired);
1158 		PR_DECR_KSTAT(pr_retired);
1159 		PR_INCR_KSTAT(pr_unretired);
1160 		return (page_retire_done(pp, PRD_UNR_SUCCESS));
1161 	}
1162 	PR_DEBUG(prd_unotlocked);
1163 	return (page_retire_done(pp, PRD_UNR_CANTLOCK));
1164 }
1165 
1166 /*
1167  * Return a page to service by moving it from the retired_pages vnode
1168  * onto the freelist.
1169  *
1170  * Called from mmioctl_page_retire() on behalf of the FMA DE.
1171  *
1172  * Returns:
1173  *
1174  *   - 0 if the page is unretired,
1175  *   - EAGAIN if the pp can not be locked,
1176  *   - EINVAL if the PA is whacko, and
1177  *   - EIO if the pp is not retired.
1178  */
1179 int
1180 page_unretire(uint64_t pa)
1181 {
1182 	page_t	*pp;
1183 
1184 	pp = page_numtopp_nolock(mmu_btop(pa));
1185 	if (pp == NULL) {
1186 		return (page_retire_done(pp, PRD_INVALID_PA));
1187 	}
1188 
1189 	return (page_unretire_pp(pp, PR_UNR_FREE));
1190 }
1191 
1192 /*
1193  * Test a page to see if it is retired. If errors is non-NULL, the toxic
1194  * bits of the page are returned. Returns 0 on success, error code on failure.
1195  */
1196 int
1197 page_retire_check_pp(page_t *pp, uint64_t *errors)
1198 {
1199 	int rc;
1200 
1201 	if (PP_RETIRED(pp)) {
1202 		PR_DEBUG(prd_checkhit);
1203 		rc = 0;
1204 	} else if (PP_PR_REQ(pp)) {
1205 		PR_DEBUG(prd_checkmiss_pend);
1206 		rc = EAGAIN;
1207 	} else {
1208 		PR_DEBUG(prd_checkmiss_noerr);
1209 		rc = EIO;
1210 	}
1211 
1212 	/*
1213 	 * We have magically arranged the bit values returned to fmd(1M)
1214 	 * to line up with the FMA, MCE, and UE bits of the page_t.
1215 	 */
1216 	if (errors) {
1217 		uint64_t toxic = (uint64_t)(pp->p_toxic & PR_ERRMASK);
1218 		if (toxic & PR_UE_SCRUBBED) {
1219 			toxic &= ~PR_UE_SCRUBBED;
1220 			toxic |= PR_UE;
1221 		}
1222 		*errors = toxic;
1223 	}
1224 
1225 	return (rc);
1226 }
1227 
1228 /*
1229  * Test to see if the page_t for a given PA is retired, and return the
1230  * hardware errors we have seen on the page if requested.
1231  *
1232  * Called from mmioctl_page_retire on behalf of the FMA DE.
1233  *
1234  * Returns:
1235  *
1236  *   - 0 if the page is retired,
1237  *   - EIO if the page is not retired and has no errors,
1238  *   - EAGAIN if the page is not retired but is pending; and
1239  *   - EINVAL if the PA is whacko.
1240  */
1241 int
1242 page_retire_check(uint64_t pa, uint64_t *errors)
1243 {
1244 	page_t	*pp;
1245 
1246 	if (errors) {
1247 		*errors = 0;
1248 	}
1249 
1250 	pp = page_numtopp_nolock(mmu_btop(pa));
1251 	if (pp == NULL) {
1252 		return (page_retire_done(pp, PRD_INVALID_PA));
1253 	}
1254 
1255 	return (page_retire_check_pp(pp, errors));
1256 }
1257 
1258 /*
1259  * Page retire self-test. For now, it always returns 0.
1260  */
1261 int
1262 page_retire_test(void)
1263 {
1264 	page_t *first, *pp, *cpp, *cpp2, *lpp;
1265 
1266 	/*
1267 	 * Tests the corner case where a large page can't be retired
1268 	 * because one of the constituent pages is locked. We mark
1269 	 * one page to be retired and try to retire it, and mark the
1270 	 * other page to be retired but don't try to retire it, so
1271 	 * that page_unlock() in the failure path will recurse and try
1272 	 * to retire THAT page. This is the worst possible situation
1273 	 * we can get ourselves into.
1274 	 */
1275 	memsegs_lock(0);
1276 	pp = first = page_first();
1277 	do {
1278 		if (pp->p_szc && PP_PAGEROOT(pp) == pp) {
1279 			cpp = pp + 1;
1280 			lpp = PP_ISFREE(pp)? pp : pp + 2;
1281 			cpp2 = pp + 3;
1282 			if (!page_trylock(lpp, pp == lpp? SE_EXCL : SE_SHARED))
1283 				continue;
1284 			if (!page_trylock(cpp, SE_EXCL)) {
1285 				page_unlock(lpp);
1286 				continue;
1287 			}
1288 
1289 			/* fails */
1290 			(void) page_retire(ptob(cpp->p_pagenum), PR_FMA);
1291 
1292 			page_unlock(lpp);
1293 			page_unlock(cpp);
1294 			(void) page_retire(ptob(cpp->p_pagenum), PR_FMA);
1295 			(void) page_retire(ptob(cpp2->p_pagenum), PR_FMA);
1296 		}
1297 	} while ((pp = page_next(pp)) != first);
1298 	memsegs_unlock(0);
1299 
1300 	return (0);
1301 }
1302