1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
4 * Copyright (c) 2010 David Chinner.
5 * Copyright (c) 2011 Christoph Hellwig.
6 * All Rights Reserved.
7 */
8 #include "xfs_platform.h"
9 #include "xfs_fs.h"
10 #include "xfs_format.h"
11 #include "xfs_log_format.h"
12 #include "xfs_shared.h"
13 #include "xfs_trans_resv.h"
14 #include "xfs_mount.h"
15 #include "xfs_alloc.h"
16 #include "xfs_extent_busy.h"
17 #include "xfs_trace.h"
18 #include "xfs_trans.h"
19 #include "xfs_log.h"
20 #include "xfs_ag.h"
21 #include "xfs_rtgroup.h"
22
23 struct xfs_extent_busy_tree {
24 spinlock_t eb_lock;
25 struct rb_root eb_tree;
26 unsigned int eb_gen;
27 wait_queue_head_t eb_wait;
28 };
29
30 static void
xfs_extent_busy_insert_list(struct xfs_group * xg,xfs_agblock_t bno,xfs_extlen_t len,unsigned int flags,struct list_head * busy_list)31 xfs_extent_busy_insert_list(
32 struct xfs_group *xg,
33 xfs_agblock_t bno,
34 xfs_extlen_t len,
35 unsigned int flags,
36 struct list_head *busy_list)
37 {
38 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
39 struct xfs_extent_busy *new;
40 struct xfs_extent_busy *busyp;
41 struct rb_node **rbp;
42 struct rb_node *parent = NULL;
43
44 new = kzalloc_obj(struct xfs_extent_busy, GFP_KERNEL | __GFP_NOFAIL);
45 new->group = xfs_group_hold(xg);
46 new->bno = bno;
47 new->length = len;
48 INIT_LIST_HEAD(&new->list);
49 new->flags = flags;
50
51 /* trace before insert to be able to see failed inserts */
52 trace_xfs_extent_busy(xg, bno, len);
53
54 spin_lock(&eb->eb_lock);
55 rbp = &eb->eb_tree.rb_node;
56 while (*rbp) {
57 parent = *rbp;
58 busyp = rb_entry(parent, struct xfs_extent_busy, rb_node);
59
60 if (new->bno < busyp->bno) {
61 rbp = &(*rbp)->rb_left;
62 ASSERT(new->bno + new->length <= busyp->bno);
63 } else if (new->bno > busyp->bno) {
64 rbp = &(*rbp)->rb_right;
65 ASSERT(bno >= busyp->bno + busyp->length);
66 } else {
67 ASSERT(0);
68 }
69 }
70
71 rb_link_node(&new->rb_node, parent, rbp);
72 rb_insert_color(&new->rb_node, &eb->eb_tree);
73
74 /* always process discard lists in fifo order */
75 list_add_tail(&new->list, busy_list);
76 spin_unlock(&eb->eb_lock);
77 }
78
79 void
xfs_extent_busy_insert(struct xfs_trans * tp,struct xfs_group * xg,xfs_agblock_t bno,xfs_extlen_t len,unsigned int flags)80 xfs_extent_busy_insert(
81 struct xfs_trans *tp,
82 struct xfs_group *xg,
83 xfs_agblock_t bno,
84 xfs_extlen_t len,
85 unsigned int flags)
86 {
87 xfs_extent_busy_insert_list(xg, bno, len, flags, &tp->t_busy);
88 }
89
90 void
xfs_extent_busy_insert_discard(struct xfs_group * xg,xfs_agblock_t bno,xfs_extlen_t len,struct list_head * busy_list)91 xfs_extent_busy_insert_discard(
92 struct xfs_group *xg,
93 xfs_agblock_t bno,
94 xfs_extlen_t len,
95 struct list_head *busy_list)
96 {
97 xfs_extent_busy_insert_list(xg, bno, len, XFS_EXTENT_BUSY_DISCARDED,
98 busy_list);
99 }
100
101 /*
102 * Search for a busy extent within the range of the extent we are about to
103 * allocate. You need to be holding the busy extent tree lock when calling
104 * xfs_extent_busy_search(). This function returns 0 for no overlapping busy
105 * extent, -1 for an overlapping but not exact busy extent, and 1 for an exact
106 * match. This is done so that a non-zero return indicates an overlap that
107 * will require a synchronous transaction, but it can still be
108 * used to distinguish between a partial or exact match.
109 */
110 int
xfs_extent_busy_search(struct xfs_group * xg,xfs_agblock_t bno,xfs_extlen_t len)111 xfs_extent_busy_search(
112 struct xfs_group *xg,
113 xfs_agblock_t bno,
114 xfs_extlen_t len)
115 {
116 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
117 struct rb_node *rbp;
118 struct xfs_extent_busy *busyp;
119 int match = 0;
120
121 /* find closest start bno overlap */
122 spin_lock(&eb->eb_lock);
123 rbp = eb->eb_tree.rb_node;
124 while (rbp) {
125 busyp = rb_entry(rbp, struct xfs_extent_busy, rb_node);
126 if (bno < busyp->bno) {
127 /* may overlap, but exact start block is lower */
128 if (bno + len > busyp->bno)
129 match = -1;
130 rbp = rbp->rb_left;
131 } else if (bno > busyp->bno) {
132 /* may overlap, but exact start block is higher */
133 if (bno < busyp->bno + busyp->length)
134 match = -1;
135 rbp = rbp->rb_right;
136 } else {
137 /* bno matches busyp, length determines exact match */
138 match = (busyp->length == len) ? 1 : -1;
139 break;
140 }
141 }
142 spin_unlock(&eb->eb_lock);
143 return match;
144 }
145
146 /*
147 * The found free extent [fbno, fend] overlaps part or all of the given busy
148 * extent. If the overlap covers the beginning, the end, or all of the busy
149 * extent, the overlapping portion can be made unbusy and used for the
150 * allocation. We can't split a busy extent because we can't modify a
151 * transaction/CIL context busy list, but we can update an entry's block
152 * number or length.
153 *
154 * Returns true if the extent can safely be reused, or false if the search
155 * needs to be restarted.
156 */
157 STATIC bool
xfs_extent_busy_update_extent(struct xfs_group * xg,struct xfs_extent_busy * busyp,xfs_agblock_t fbno,xfs_extlen_t flen,bool userdata)158 xfs_extent_busy_update_extent(
159 struct xfs_group *xg,
160 struct xfs_extent_busy *busyp,
161 xfs_agblock_t fbno,
162 xfs_extlen_t flen,
163 bool userdata)
164 __releases(&eb->eb_lock)
165 __acquires(&eb->eb_lock)
166 {
167 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
168 xfs_agblock_t fend = fbno + flen;
169 xfs_agblock_t bbno = busyp->bno;
170 xfs_agblock_t bend = bbno + busyp->length;
171
172 /*
173 * This extent is currently being discarded. Give the thread
174 * performing the discard a chance to mark the extent unbusy
175 * and retry.
176 */
177 if (busyp->flags & XFS_EXTENT_BUSY_DISCARDED) {
178 spin_unlock(&eb->eb_lock);
179 delay(1);
180 spin_lock(&eb->eb_lock);
181 return false;
182 }
183
184 /*
185 * If there is a busy extent overlapping a user allocation, we have
186 * no choice but to force the log and retry the search.
187 *
188 * Fortunately this does not happen during normal operation, but
189 * only if the filesystem is very low on space and has to dip into
190 * the AGFL for normal allocations.
191 */
192 if (userdata)
193 goto out_force_log;
194
195 if (bbno < fbno && bend > fend) {
196 /*
197 * Case 1:
198 * bbno bend
199 * +BBBBBBBBBBBBBBBBB+
200 * +---------+
201 * fbno fend
202 */
203
204 /*
205 * We would have to split the busy extent to be able to track
206 * it correct, which we cannot do because we would have to
207 * modify the list of busy extents attached to the transaction
208 * or CIL context, which is immutable.
209 *
210 * Force out the log to clear the busy extent and retry the
211 * search.
212 */
213 goto out_force_log;
214 } else if (bbno >= fbno && bend <= fend) {
215 /*
216 * Case 2:
217 * bbno bend
218 * +BBBBBBBBBBBBBBBBB+
219 * +-----------------+
220 * fbno fend
221 *
222 * Case 3:
223 * bbno bend
224 * +BBBBBBBBBBBBBBBBB+
225 * +--------------------------+
226 * fbno fend
227 *
228 * Case 4:
229 * bbno bend
230 * +BBBBBBBBBBBBBBBBB+
231 * +--------------------------+
232 * fbno fend
233 *
234 * Case 5:
235 * bbno bend
236 * +BBBBBBBBBBBBBBBBB+
237 * +-----------------------------------+
238 * fbno fend
239 *
240 */
241
242 /*
243 * The busy extent is fully covered by the extent we are
244 * allocating, and can simply be removed from the rbtree.
245 * However we cannot remove it from the immutable list
246 * tracking busy extents in the transaction or CIL context,
247 * so set the length to zero to mark it invalid.
248 *
249 * We also need to restart the busy extent search from the
250 * tree root, because erasing the node can rearrange the
251 * tree topology.
252 */
253 rb_erase(&busyp->rb_node, &eb->eb_tree);
254 busyp->length = 0;
255 return false;
256 } else if (fend < bend) {
257 /*
258 * Case 6:
259 * bbno bend
260 * +BBBBBBBBBBBBBBBBB+
261 * +---------+
262 * fbno fend
263 *
264 * Case 7:
265 * bbno bend
266 * +BBBBBBBBBBBBBBBBB+
267 * +------------------+
268 * fbno fend
269 *
270 */
271 busyp->bno = fend;
272 busyp->length = bend - fend;
273 } else if (bbno < fbno) {
274 /*
275 * Case 8:
276 * bbno bend
277 * +BBBBBBBBBBBBBBBBB+
278 * +-------------+
279 * fbno fend
280 *
281 * Case 9:
282 * bbno bend
283 * +BBBBBBBBBBBBBBBBB+
284 * +----------------------+
285 * fbno fend
286 */
287 busyp->length = fbno - busyp->bno;
288 } else {
289 ASSERT(0);
290 }
291
292 trace_xfs_extent_busy_reuse(xg, fbno, flen);
293 return true;
294
295 out_force_log:
296 spin_unlock(&eb->eb_lock);
297 xfs_log_force(xg->xg_mount, XFS_LOG_SYNC);
298 trace_xfs_extent_busy_force(xg, fbno, flen);
299 spin_lock(&eb->eb_lock);
300 return false;
301 }
302
303 /*
304 * For a given extent [fbno, flen], make sure we can reuse it safely.
305 */
306 void
xfs_extent_busy_reuse(struct xfs_group * xg,xfs_agblock_t fbno,xfs_extlen_t flen,bool userdata)307 xfs_extent_busy_reuse(
308 struct xfs_group *xg,
309 xfs_agblock_t fbno,
310 xfs_extlen_t flen,
311 bool userdata)
312 {
313 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
314 struct rb_node *rbp;
315
316 ASSERT(flen > 0);
317 spin_lock(&eb->eb_lock);
318 restart:
319 rbp = eb->eb_tree.rb_node;
320 while (rbp) {
321 struct xfs_extent_busy *busyp =
322 rb_entry(rbp, struct xfs_extent_busy, rb_node);
323 xfs_agblock_t bbno = busyp->bno;
324 xfs_agblock_t bend = bbno + busyp->length;
325
326 if (fbno + flen <= bbno) {
327 rbp = rbp->rb_left;
328 continue;
329 } else if (fbno >= bend) {
330 rbp = rbp->rb_right;
331 continue;
332 }
333
334 if (!xfs_extent_busy_update_extent(xg, busyp, fbno, flen,
335 userdata))
336 goto restart;
337 }
338 spin_unlock(&eb->eb_lock);
339 }
340
341 /*
342 * For a given extent [fbno, flen], search the busy extent list to find a
343 * subset of the extent that is not busy. If *rlen is smaller than
344 * args->minlen no suitable extent could be found, and the higher level
345 * code needs to force out the log and retry the allocation.
346 *
347 * Return the current busy generation for the group if the extent is busy. This
348 * value can be used to wait for at least one of the currently busy extents
349 * to be cleared. Note that the busy list is not guaranteed to be empty after
350 * the gen is woken. The state of a specific extent must always be confirmed
351 * with another call to xfs_extent_busy_trim() before it can be used.
352 */
353 bool
xfs_extent_busy_trim(struct xfs_group * xg,xfs_extlen_t minlen,xfs_extlen_t maxlen,xfs_agblock_t * bno,xfs_extlen_t * len,unsigned * busy_gen)354 xfs_extent_busy_trim(
355 struct xfs_group *xg,
356 xfs_extlen_t minlen,
357 xfs_extlen_t maxlen,
358 xfs_agblock_t *bno,
359 xfs_extlen_t *len,
360 unsigned *busy_gen)
361 {
362 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
363 xfs_agblock_t fbno;
364 xfs_extlen_t flen;
365 struct rb_node *rbp;
366 bool ret = false;
367
368 ASSERT(*len > 0);
369
370 spin_lock(&eb->eb_lock);
371 fbno = *bno;
372 flen = *len;
373 rbp = eb->eb_tree.rb_node;
374 while (rbp && flen >= minlen) {
375 struct xfs_extent_busy *busyp =
376 rb_entry(rbp, struct xfs_extent_busy, rb_node);
377 xfs_agblock_t fend = fbno + flen;
378 xfs_agblock_t bbno = busyp->bno;
379 xfs_agblock_t bend = bbno + busyp->length;
380
381 if (fend <= bbno) {
382 rbp = rbp->rb_left;
383 continue;
384 } else if (fbno >= bend) {
385 rbp = rbp->rb_right;
386 continue;
387 }
388
389 if (bbno <= fbno) {
390 /* start overlap */
391
392 /*
393 * Case 1:
394 * bbno bend
395 * +BBBBBBBBBBBBBBBBB+
396 * +---------+
397 * fbno fend
398 *
399 * Case 2:
400 * bbno bend
401 * +BBBBBBBBBBBBBBBBB+
402 * +-------------+
403 * fbno fend
404 *
405 * Case 3:
406 * bbno bend
407 * +BBBBBBBBBBBBBBBBB+
408 * +-------------+
409 * fbno fend
410 *
411 * Case 4:
412 * bbno bend
413 * +BBBBBBBBBBBBBBBBB+
414 * +-----------------+
415 * fbno fend
416 *
417 * No unbusy region in extent, return failure.
418 */
419 if (fend <= bend)
420 goto fail;
421
422 /*
423 * Case 5:
424 * bbno bend
425 * +BBBBBBBBBBBBBBBBB+
426 * +----------------------+
427 * fbno fend
428 *
429 * Case 6:
430 * bbno bend
431 * +BBBBBBBBBBBBBBBBB+
432 * +--------------------------+
433 * fbno fend
434 *
435 * Needs to be trimmed to:
436 * +-------+
437 * fbno fend
438 */
439 fbno = bend;
440 } else if (bend >= fend) {
441 /* end overlap */
442
443 /*
444 * Case 7:
445 * bbno bend
446 * +BBBBBBBBBBBBBBBBB+
447 * +------------------+
448 * fbno fend
449 *
450 * Case 8:
451 * bbno bend
452 * +BBBBBBBBBBBBBBBBB+
453 * +--------------------------+
454 * fbno fend
455 *
456 * Needs to be trimmed to:
457 * +-------+
458 * fbno fend
459 */
460 fend = bbno;
461 } else {
462 /* middle overlap */
463
464 /*
465 * Case 9:
466 * bbno bend
467 * +BBBBBBBBBBBBBBBBB+
468 * +-----------------------------------+
469 * fbno fend
470 *
471 * Can be trimmed to:
472 * +-------+ OR +-------+
473 * fbno fend fbno fend
474 *
475 * Backward allocation leads to significant
476 * fragmentation of directories, which degrades
477 * directory performance, therefore we always want to
478 * choose the option that produces forward allocation
479 * patterns.
480 * Preferring the lower bno extent will make the next
481 * request use "fend" as the start of the next
482 * allocation; if the segment is no longer busy at
483 * that point, we'll get a contiguous allocation, but
484 * even if it is still busy, we will get a forward
485 * allocation.
486 * We try to avoid choosing the segment at "bend",
487 * because that can lead to the next allocation
488 * taking the segment at "fbno", which would be a
489 * backward allocation. We only use the segment at
490 * "fbno" if it is much larger than the current
491 * requested size, because in that case there's a
492 * good chance subsequent allocations will be
493 * contiguous.
494 */
495 if (bbno - fbno >= maxlen) {
496 /* left candidate fits perfect */
497 fend = bbno;
498 } else if (fend - bend >= maxlen * 4) {
499 /* right candidate has enough free space */
500 fbno = bend;
501 } else if (bbno - fbno >= minlen) {
502 /* left candidate fits minimum requirement */
503 fend = bbno;
504 } else {
505 goto fail;
506 }
507 }
508
509 flen = fend - fbno;
510 }
511 out:
512
513 if (fbno != *bno || flen != *len) {
514 trace_xfs_extent_busy_trim(xg, *bno, *len, fbno, flen);
515 *bno = fbno;
516 *len = flen;
517 *busy_gen = eb->eb_gen;
518 ret = true;
519 }
520 spin_unlock(&eb->eb_lock);
521 return ret;
522 fail:
523 /*
524 * Return a zero extent length as failure indications. All callers
525 * re-check if the trimmed extent satisfies the minlen requirement.
526 */
527 flen = 0;
528 goto out;
529 }
530
531 static bool
xfs_extent_busy_clear_one(struct xfs_extent_busy * busyp,bool do_discard)532 xfs_extent_busy_clear_one(
533 struct xfs_extent_busy *busyp,
534 bool do_discard)
535 {
536 struct xfs_extent_busy_tree *eb = busyp->group->xg_busy_extents;
537
538 if (busyp->length) {
539 if (do_discard &&
540 !(busyp->flags & XFS_EXTENT_BUSY_SKIP_DISCARD)) {
541 busyp->flags = XFS_EXTENT_BUSY_DISCARDED;
542 return false;
543 }
544 trace_xfs_extent_busy_clear(busyp->group, busyp->bno,
545 busyp->length);
546 rb_erase(&busyp->rb_node, &eb->eb_tree);
547 }
548
549 list_del_init(&busyp->list);
550 xfs_group_put(busyp->group);
551 kfree(busyp);
552 return true;
553 }
554
555 /*
556 * Remove all extents on the passed in list from the busy extents tree.
557 * If do_discard is set skip extents that need to be discarded, and mark
558 * these as undergoing a discard operation instead.
559 */
560 void
xfs_extent_busy_clear(struct list_head * list,bool do_discard)561 xfs_extent_busy_clear(
562 struct list_head *list,
563 bool do_discard)
564 {
565 struct xfs_extent_busy *busyp, *next;
566
567 busyp = list_first_entry_or_null(list, typeof(*busyp), list);
568 if (!busyp)
569 return;
570
571 do {
572 struct xfs_group *xg = xfs_group_hold(busyp->group);
573 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
574 bool wakeup = false;
575
576 spin_lock(&eb->eb_lock);
577 do {
578 next = list_next_entry(busyp, list);
579 if (xfs_extent_busy_clear_one(busyp, do_discard))
580 wakeup = true;
581 busyp = next;
582 } while (!list_entry_is_head(busyp, list, list) &&
583 busyp->group == xg);
584
585 if (wakeup) {
586 eb->eb_gen++;
587 wake_up_all(&eb->eb_wait);
588 }
589 spin_unlock(&eb->eb_lock);
590 xfs_group_put(xg);
591 } while (!list_entry_is_head(busyp, list, list));
592 }
593
594 /*
595 * Flush out all busy extents for this group.
596 *
597 * If the current transaction is holding busy extents, the caller may not want
598 * to wait for committed busy extents to resolve. If we are being told just to
599 * try a flush or progress has been made since we last skipped a busy extent,
600 * return immediately to allow the caller to try again.
601 *
602 * If we are freeing extents, we might actually be holding the only free extents
603 * in the transaction busy list and the log force won't resolve that situation.
604 * In this case, we must return -EAGAIN to avoid a deadlock by informing the
605 * caller it needs to commit the busy extents it holds before retrying the
606 * extent free operation.
607 */
608 int
xfs_extent_busy_flush(struct xfs_trans * tp,struct xfs_group * xg,unsigned busy_gen,uint32_t alloc_flags)609 xfs_extent_busy_flush(
610 struct xfs_trans *tp,
611 struct xfs_group *xg,
612 unsigned busy_gen,
613 uint32_t alloc_flags)
614 {
615 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
616 DEFINE_WAIT (wait);
617 int error;
618
619 error = xfs_log_force(tp->t_mountp, XFS_LOG_SYNC);
620 if (error)
621 return error;
622
623 /* Avoid deadlocks on uncommitted busy extents. */
624 if (!list_empty(&tp->t_busy)) {
625 if (alloc_flags & XFS_ALLOC_FLAG_TRYFLUSH)
626 return 0;
627
628 if (busy_gen != READ_ONCE(eb->eb_gen))
629 return 0;
630
631 if (alloc_flags & XFS_ALLOC_FLAG_FREEING)
632 return -EAGAIN;
633 }
634
635 /* Wait for committed busy extents to resolve. */
636 do {
637 prepare_to_wait(&eb->eb_wait, &wait, TASK_KILLABLE);
638 if (busy_gen != READ_ONCE(eb->eb_gen))
639 break;
640 schedule();
641 } while (1);
642
643 finish_wait(&eb->eb_wait, &wait);
644 return 0;
645 }
646
647 static void
xfs_extent_busy_wait_group(struct xfs_group * xg)648 xfs_extent_busy_wait_group(
649 struct xfs_group *xg)
650 {
651 DEFINE_WAIT (wait);
652 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
653
654 do {
655 prepare_to_wait(&eb->eb_wait, &wait, TASK_KILLABLE);
656 if (RB_EMPTY_ROOT(&eb->eb_tree))
657 break;
658 schedule();
659 } while (1);
660 finish_wait(&eb->eb_wait, &wait);
661 }
662
663 void
xfs_extent_busy_wait_all(struct xfs_mount * mp)664 xfs_extent_busy_wait_all(
665 struct xfs_mount *mp)
666 {
667 struct xfs_perag *pag = NULL;
668 struct xfs_rtgroup *rtg = NULL;
669
670 while ((pag = xfs_perag_next(mp, pag)))
671 xfs_extent_busy_wait_group(pag_group(pag));
672
673 if (xfs_has_rtgroups(mp) && !xfs_has_zoned(mp))
674 while ((rtg = xfs_rtgroup_next(mp, rtg)))
675 xfs_extent_busy_wait_group(rtg_group(rtg));
676 }
677
678 /*
679 * Callback for list_sort to sort busy extents by the group they reside in.
680 */
681 int
xfs_extent_busy_ag_cmp(void * priv,const struct list_head * l1,const struct list_head * l2)682 xfs_extent_busy_ag_cmp(
683 void *priv,
684 const struct list_head *l1,
685 const struct list_head *l2)
686 {
687 struct xfs_extent_busy *b1 =
688 container_of(l1, struct xfs_extent_busy, list);
689 struct xfs_extent_busy *b2 =
690 container_of(l2, struct xfs_extent_busy, list);
691 s32 diff;
692
693 diff = b1->group->xg_gno - b2->group->xg_gno;
694 if (!diff)
695 diff = b1->bno - b2->bno;
696 return diff;
697 }
698
699 /* Are there any busy extents in this group? */
700 bool
xfs_extent_busy_list_empty(struct xfs_group * xg,unsigned * busy_gen)701 xfs_extent_busy_list_empty(
702 struct xfs_group *xg,
703 unsigned *busy_gen)
704 {
705 struct xfs_extent_busy_tree *eb = xg->xg_busy_extents;
706 bool res;
707
708 spin_lock(&eb->eb_lock);
709 res = RB_EMPTY_ROOT(&eb->eb_tree);
710 *busy_gen = READ_ONCE(eb->eb_gen);
711 spin_unlock(&eb->eb_lock);
712 return res;
713 }
714
715 struct xfs_extent_busy_tree *
xfs_extent_busy_alloc(void)716 xfs_extent_busy_alloc(void)
717 {
718 struct xfs_extent_busy_tree *eb;
719
720 eb = kzalloc_obj(*eb);
721 if (!eb)
722 return NULL;
723 spin_lock_init(&eb->eb_lock);
724 init_waitqueue_head(&eb->eb_wait);
725 eb->eb_tree = RB_ROOT;
726 return eb;
727 }
728