xref: /openbmc/linux/fs/xfs/xfs_buf.c (revision be58f710)
1  // SPDX-License-Identifier: GPL-2.0
2  /*
3   * Copyright (c) 2000-2006 Silicon Graphics, Inc.
4   * All Rights Reserved.
5   */
6  #include "xfs.h"
7  #include <linux/backing-dev.h>
8  
9  #include "xfs_shared.h"
10  #include "xfs_format.h"
11  #include "xfs_log_format.h"
12  #include "xfs_trans_resv.h"
13  #include "xfs_mount.h"
14  #include "xfs_trace.h"
15  #include "xfs_log.h"
16  #include "xfs_log_recover.h"
17  #include "xfs_trans.h"
18  #include "xfs_buf_item.h"
19  #include "xfs_errortag.h"
20  #include "xfs_error.h"
21  #include "xfs_ag.h"
22  
23  static kmem_zone_t *xfs_buf_zone;
24  
25  /*
26   * Locking orders
27   *
28   * xfs_buf_ioacct_inc:
29   * xfs_buf_ioacct_dec:
30   *	b_sema (caller holds)
31   *	  b_lock
32   *
33   * xfs_buf_stale:
34   *	b_sema (caller holds)
35   *	  b_lock
36   *	    lru_lock
37   *
38   * xfs_buf_rele:
39   *	b_lock
40   *	  pag_buf_lock
41   *	    lru_lock
42   *
43   * xfs_buftarg_drain_rele
44   *	lru_lock
45   *	  b_lock (trylock due to inversion)
46   *
47   * xfs_buftarg_isolate
48   *	lru_lock
49   *	  b_lock (trylock due to inversion)
50   */
51  
52  static int __xfs_buf_submit(struct xfs_buf *bp, bool wait);
53  
54  static inline int
55  xfs_buf_submit(
56  	struct xfs_buf		*bp)
57  {
58  	return __xfs_buf_submit(bp, !(bp->b_flags & XBF_ASYNC));
59  }
60  
61  static inline int
62  xfs_buf_is_vmapped(
63  	struct xfs_buf	*bp)
64  {
65  	/*
66  	 * Return true if the buffer is vmapped.
67  	 *
68  	 * b_addr is null if the buffer is not mapped, but the code is clever
69  	 * enough to know it doesn't have to map a single page, so the check has
70  	 * to be both for b_addr and bp->b_page_count > 1.
71  	 */
72  	return bp->b_addr && bp->b_page_count > 1;
73  }
74  
75  static inline int
76  xfs_buf_vmap_len(
77  	struct xfs_buf	*bp)
78  {
79  	return (bp->b_page_count * PAGE_SIZE);
80  }
81  
82  /*
83   * Bump the I/O in flight count on the buftarg if we haven't yet done so for
84   * this buffer. The count is incremented once per buffer (per hold cycle)
85   * because the corresponding decrement is deferred to buffer release. Buffers
86   * can undergo I/O multiple times in a hold-release cycle and per buffer I/O
87   * tracking adds unnecessary overhead. This is used for sychronization purposes
88   * with unmount (see xfs_buftarg_drain()), so all we really need is a count of
89   * in-flight buffers.
90   *
91   * Buffers that are never released (e.g., superblock, iclog buffers) must set
92   * the XBF_NO_IOACCT flag before I/O submission. Otherwise, the buftarg count
93   * never reaches zero and unmount hangs indefinitely.
94   */
95  static inline void
96  xfs_buf_ioacct_inc(
97  	struct xfs_buf	*bp)
98  {
99  	if (bp->b_flags & XBF_NO_IOACCT)
100  		return;
101  
102  	ASSERT(bp->b_flags & XBF_ASYNC);
103  	spin_lock(&bp->b_lock);
104  	if (!(bp->b_state & XFS_BSTATE_IN_FLIGHT)) {
105  		bp->b_state |= XFS_BSTATE_IN_FLIGHT;
106  		percpu_counter_inc(&bp->b_target->bt_io_count);
107  	}
108  	spin_unlock(&bp->b_lock);
109  }
110  
111  /*
112   * Clear the in-flight state on a buffer about to be released to the LRU or
113   * freed and unaccount from the buftarg.
114   */
115  static inline void
116  __xfs_buf_ioacct_dec(
117  	struct xfs_buf	*bp)
118  {
119  	lockdep_assert_held(&bp->b_lock);
120  
121  	if (bp->b_state & XFS_BSTATE_IN_FLIGHT) {
122  		bp->b_state &= ~XFS_BSTATE_IN_FLIGHT;
123  		percpu_counter_dec(&bp->b_target->bt_io_count);
124  	}
125  }
126  
127  static inline void
128  xfs_buf_ioacct_dec(
129  	struct xfs_buf	*bp)
130  {
131  	spin_lock(&bp->b_lock);
132  	__xfs_buf_ioacct_dec(bp);
133  	spin_unlock(&bp->b_lock);
134  }
135  
136  /*
137   * When we mark a buffer stale, we remove the buffer from the LRU and clear the
138   * b_lru_ref count so that the buffer is freed immediately when the buffer
139   * reference count falls to zero. If the buffer is already on the LRU, we need
140   * to remove the reference that LRU holds on the buffer.
141   *
142   * This prevents build-up of stale buffers on the LRU.
143   */
144  void
145  xfs_buf_stale(
146  	struct xfs_buf	*bp)
147  {
148  	ASSERT(xfs_buf_islocked(bp));
149  
150  	bp->b_flags |= XBF_STALE;
151  
152  	/*
153  	 * Clear the delwri status so that a delwri queue walker will not
154  	 * flush this buffer to disk now that it is stale. The delwri queue has
155  	 * a reference to the buffer, so this is safe to do.
156  	 */
157  	bp->b_flags &= ~_XBF_DELWRI_Q;
158  
159  	/*
160  	 * Once the buffer is marked stale and unlocked, a subsequent lookup
161  	 * could reset b_flags. There is no guarantee that the buffer is
162  	 * unaccounted (released to LRU) before that occurs. Drop in-flight
163  	 * status now to preserve accounting consistency.
164  	 */
165  	spin_lock(&bp->b_lock);
166  	__xfs_buf_ioacct_dec(bp);
167  
168  	atomic_set(&bp->b_lru_ref, 0);
169  	if (!(bp->b_state & XFS_BSTATE_DISPOSE) &&
170  	    (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru)))
171  		atomic_dec(&bp->b_hold);
172  
173  	ASSERT(atomic_read(&bp->b_hold) >= 1);
174  	spin_unlock(&bp->b_lock);
175  }
176  
177  static int
178  xfs_buf_get_maps(
179  	struct xfs_buf		*bp,
180  	int			map_count)
181  {
182  	ASSERT(bp->b_maps == NULL);
183  	bp->b_map_count = map_count;
184  
185  	if (map_count == 1) {
186  		bp->b_maps = &bp->__b_map;
187  		return 0;
188  	}
189  
190  	bp->b_maps = kmem_zalloc(map_count * sizeof(struct xfs_buf_map),
191  				KM_NOFS);
192  	if (!bp->b_maps)
193  		return -ENOMEM;
194  	return 0;
195  }
196  
197  /*
198   *	Frees b_pages if it was allocated.
199   */
200  static void
201  xfs_buf_free_maps(
202  	struct xfs_buf	*bp)
203  {
204  	if (bp->b_maps != &bp->__b_map) {
205  		kmem_free(bp->b_maps);
206  		bp->b_maps = NULL;
207  	}
208  }
209  
210  static int
211  _xfs_buf_alloc(
212  	struct xfs_buftarg	*target,
213  	struct xfs_buf_map	*map,
214  	int			nmaps,
215  	xfs_buf_flags_t		flags,
216  	struct xfs_buf		**bpp)
217  {
218  	struct xfs_buf		*bp;
219  	int			error;
220  	int			i;
221  
222  	*bpp = NULL;
223  	bp = kmem_cache_zalloc(xfs_buf_zone, GFP_NOFS | __GFP_NOFAIL);
224  
225  	/*
226  	 * We don't want certain flags to appear in b_flags unless they are
227  	 * specifically set by later operations on the buffer.
228  	 */
229  	flags &= ~(XBF_UNMAPPED | XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD);
230  
231  	atomic_set(&bp->b_hold, 1);
232  	atomic_set(&bp->b_lru_ref, 1);
233  	init_completion(&bp->b_iowait);
234  	INIT_LIST_HEAD(&bp->b_lru);
235  	INIT_LIST_HEAD(&bp->b_list);
236  	INIT_LIST_HEAD(&bp->b_li_list);
237  	sema_init(&bp->b_sema, 0); /* held, no waiters */
238  	spin_lock_init(&bp->b_lock);
239  	bp->b_target = target;
240  	bp->b_mount = target->bt_mount;
241  	bp->b_flags = flags;
242  
243  	/*
244  	 * Set length and io_length to the same value initially.
245  	 * I/O routines should use io_length, which will be the same in
246  	 * most cases but may be reset (e.g. XFS recovery).
247  	 */
248  	error = xfs_buf_get_maps(bp, nmaps);
249  	if (error)  {
250  		kmem_cache_free(xfs_buf_zone, bp);
251  		return error;
252  	}
253  
254  	bp->b_rhash_key = map[0].bm_bn;
255  	bp->b_length = 0;
256  	for (i = 0; i < nmaps; i++) {
257  		bp->b_maps[i].bm_bn = map[i].bm_bn;
258  		bp->b_maps[i].bm_len = map[i].bm_len;
259  		bp->b_length += map[i].bm_len;
260  	}
261  
262  	atomic_set(&bp->b_pin_count, 0);
263  	init_waitqueue_head(&bp->b_waiters);
264  
265  	XFS_STATS_INC(bp->b_mount, xb_create);
266  	trace_xfs_buf_init(bp, _RET_IP_);
267  
268  	*bpp = bp;
269  	return 0;
270  }
271  
272  static void
273  xfs_buf_free_pages(
274  	struct xfs_buf	*bp)
275  {
276  	uint		i;
277  
278  	ASSERT(bp->b_flags & _XBF_PAGES);
279  
280  	if (xfs_buf_is_vmapped(bp))
281  		vm_unmap_ram(bp->b_addr, bp->b_page_count);
282  
283  	for (i = 0; i < bp->b_page_count; i++) {
284  		if (bp->b_pages[i])
285  			__free_page(bp->b_pages[i]);
286  	}
287  	if (current->reclaim_state)
288  		current->reclaim_state->reclaimed_slab += bp->b_page_count;
289  
290  	if (bp->b_pages != bp->b_page_array)
291  		kmem_free(bp->b_pages);
292  	bp->b_pages = NULL;
293  	bp->b_flags &= ~_XBF_PAGES;
294  }
295  
296  static void
297  xfs_buf_free(
298  	struct xfs_buf		*bp)
299  {
300  	trace_xfs_buf_free(bp, _RET_IP_);
301  
302  	ASSERT(list_empty(&bp->b_lru));
303  
304  	if (bp->b_flags & _XBF_PAGES)
305  		xfs_buf_free_pages(bp);
306  	else if (bp->b_flags & _XBF_KMEM)
307  		kmem_free(bp->b_addr);
308  
309  	xfs_buf_free_maps(bp);
310  	kmem_cache_free(xfs_buf_zone, bp);
311  }
312  
313  static int
314  xfs_buf_alloc_kmem(
315  	struct xfs_buf	*bp,
316  	xfs_buf_flags_t	flags)
317  {
318  	xfs_km_flags_t	kmflag_mask = KM_NOFS;
319  	size_t		size = BBTOB(bp->b_length);
320  
321  	/* Assure zeroed buffer for non-read cases. */
322  	if (!(flags & XBF_READ))
323  		kmflag_mask |= KM_ZERO;
324  
325  	bp->b_addr = kmem_alloc(size, kmflag_mask);
326  	if (!bp->b_addr)
327  		return -ENOMEM;
328  
329  	if (((unsigned long)(bp->b_addr + size - 1) & PAGE_MASK) !=
330  	    ((unsigned long)bp->b_addr & PAGE_MASK)) {
331  		/* b_addr spans two pages - use alloc_page instead */
332  		kmem_free(bp->b_addr);
333  		bp->b_addr = NULL;
334  		return -ENOMEM;
335  	}
336  	bp->b_offset = offset_in_page(bp->b_addr);
337  	bp->b_pages = bp->b_page_array;
338  	bp->b_pages[0] = kmem_to_page(bp->b_addr);
339  	bp->b_page_count = 1;
340  	bp->b_flags |= _XBF_KMEM;
341  	return 0;
342  }
343  
344  static int
345  xfs_buf_alloc_pages(
346  	struct xfs_buf	*bp,
347  	xfs_buf_flags_t	flags)
348  {
349  	gfp_t		gfp_mask = __GFP_NOWARN;
350  	long		filled = 0;
351  
352  	if (flags & XBF_READ_AHEAD)
353  		gfp_mask |= __GFP_NORETRY;
354  	else
355  		gfp_mask |= GFP_NOFS;
356  
357  	/* Make sure that we have a page list */
358  	bp->b_page_count = DIV_ROUND_UP(BBTOB(bp->b_length), PAGE_SIZE);
359  	if (bp->b_page_count <= XB_PAGES) {
360  		bp->b_pages = bp->b_page_array;
361  	} else {
362  		bp->b_pages = kzalloc(sizeof(struct page *) * bp->b_page_count,
363  					gfp_mask);
364  		if (!bp->b_pages)
365  			return -ENOMEM;
366  	}
367  	bp->b_flags |= _XBF_PAGES;
368  
369  	/* Assure zeroed buffer for non-read cases. */
370  	if (!(flags & XBF_READ))
371  		gfp_mask |= __GFP_ZERO;
372  
373  	/*
374  	 * Bulk filling of pages can take multiple calls. Not filling the entire
375  	 * array is not an allocation failure, so don't back off if we get at
376  	 * least one extra page.
377  	 */
378  	for (;;) {
379  		long	last = filled;
380  
381  		filled = alloc_pages_bulk_array(gfp_mask, bp->b_page_count,
382  						bp->b_pages);
383  		if (filled == bp->b_page_count) {
384  			XFS_STATS_INC(bp->b_mount, xb_page_found);
385  			break;
386  		}
387  
388  		if (filled != last)
389  			continue;
390  
391  		if (flags & XBF_READ_AHEAD) {
392  			xfs_buf_free_pages(bp);
393  			return -ENOMEM;
394  		}
395  
396  		XFS_STATS_INC(bp->b_mount, xb_page_retries);
397  		congestion_wait(BLK_RW_ASYNC, HZ / 50);
398  	}
399  	return 0;
400  }
401  
402  /*
403   *	Map buffer into kernel address-space if necessary.
404   */
405  STATIC int
406  _xfs_buf_map_pages(
407  	struct xfs_buf		*bp,
408  	uint			flags)
409  {
410  	ASSERT(bp->b_flags & _XBF_PAGES);
411  	if (bp->b_page_count == 1) {
412  		/* A single page buffer is always mappable */
413  		bp->b_addr = page_address(bp->b_pages[0]);
414  	} else if (flags & XBF_UNMAPPED) {
415  		bp->b_addr = NULL;
416  	} else {
417  		int retried = 0;
418  		unsigned nofs_flag;
419  
420  		/*
421  		 * vm_map_ram() will allocate auxiliary structures (e.g.
422  		 * pagetables) with GFP_KERNEL, yet we are likely to be under
423  		 * GFP_NOFS context here. Hence we need to tell memory reclaim
424  		 * that we are in such a context via PF_MEMALLOC_NOFS to prevent
425  		 * memory reclaim re-entering the filesystem here and
426  		 * potentially deadlocking.
427  		 */
428  		nofs_flag = memalloc_nofs_save();
429  		do {
430  			bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count,
431  						-1);
432  			if (bp->b_addr)
433  				break;
434  			vm_unmap_aliases();
435  		} while (retried++ <= 1);
436  		memalloc_nofs_restore(nofs_flag);
437  
438  		if (!bp->b_addr)
439  			return -ENOMEM;
440  	}
441  
442  	return 0;
443  }
444  
445  /*
446   *	Finding and Reading Buffers
447   */
448  static int
449  _xfs_buf_obj_cmp(
450  	struct rhashtable_compare_arg	*arg,
451  	const void			*obj)
452  {
453  	const struct xfs_buf_map	*map = arg->key;
454  	const struct xfs_buf		*bp = obj;
455  
456  	/*
457  	 * The key hashing in the lookup path depends on the key being the
458  	 * first element of the compare_arg, make sure to assert this.
459  	 */
460  	BUILD_BUG_ON(offsetof(struct xfs_buf_map, bm_bn) != 0);
461  
462  	if (bp->b_rhash_key != map->bm_bn)
463  		return 1;
464  
465  	if (unlikely(bp->b_length != map->bm_len)) {
466  		/*
467  		 * found a block number match. If the range doesn't
468  		 * match, the only way this is allowed is if the buffer
469  		 * in the cache is stale and the transaction that made
470  		 * it stale has not yet committed. i.e. we are
471  		 * reallocating a busy extent. Skip this buffer and
472  		 * continue searching for an exact match.
473  		 */
474  		ASSERT(bp->b_flags & XBF_STALE);
475  		return 1;
476  	}
477  	return 0;
478  }
479  
480  static const struct rhashtable_params xfs_buf_hash_params = {
481  	.min_size		= 32,	/* empty AGs have minimal footprint */
482  	.nelem_hint		= 16,
483  	.key_len		= sizeof(xfs_daddr_t),
484  	.key_offset		= offsetof(struct xfs_buf, b_rhash_key),
485  	.head_offset		= offsetof(struct xfs_buf, b_rhash_head),
486  	.automatic_shrinking	= true,
487  	.obj_cmpfn		= _xfs_buf_obj_cmp,
488  };
489  
490  int
491  xfs_buf_hash_init(
492  	struct xfs_perag	*pag)
493  {
494  	spin_lock_init(&pag->pag_buf_lock);
495  	return rhashtable_init(&pag->pag_buf_hash, &xfs_buf_hash_params);
496  }
497  
498  void
499  xfs_buf_hash_destroy(
500  	struct xfs_perag	*pag)
501  {
502  	rhashtable_destroy(&pag->pag_buf_hash);
503  }
504  
505  /*
506   * Look up a buffer in the buffer cache and return it referenced and locked
507   * in @found_bp.
508   *
509   * If @new_bp is supplied and we have a lookup miss, insert @new_bp into the
510   * cache.
511   *
512   * If XBF_TRYLOCK is set in @flags, only try to lock the buffer and return
513   * -EAGAIN if we fail to lock it.
514   *
515   * Return values are:
516   *	-EFSCORRUPTED if have been supplied with an invalid address
517   *	-EAGAIN on trylock failure
518   *	-ENOENT if we fail to find a match and @new_bp was NULL
519   *	0, with @found_bp:
520   *		- @new_bp if we inserted it into the cache
521   *		- the buffer we found and locked.
522   */
523  static int
524  xfs_buf_find(
525  	struct xfs_buftarg	*btp,
526  	struct xfs_buf_map	*map,
527  	int			nmaps,
528  	xfs_buf_flags_t		flags,
529  	struct xfs_buf		*new_bp,
530  	struct xfs_buf		**found_bp)
531  {
532  	struct xfs_perag	*pag;
533  	struct xfs_buf		*bp;
534  	struct xfs_buf_map	cmap = { .bm_bn = map[0].bm_bn };
535  	xfs_daddr_t		eofs;
536  	int			i;
537  
538  	*found_bp = NULL;
539  
540  	for (i = 0; i < nmaps; i++)
541  		cmap.bm_len += map[i].bm_len;
542  
543  	/* Check for IOs smaller than the sector size / not sector aligned */
544  	ASSERT(!(BBTOB(cmap.bm_len) < btp->bt_meta_sectorsize));
545  	ASSERT(!(BBTOB(cmap.bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
546  
547  	/*
548  	 * Corrupted block numbers can get through to here, unfortunately, so we
549  	 * have to check that the buffer falls within the filesystem bounds.
550  	 */
551  	eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);
552  	if (cmap.bm_bn < 0 || cmap.bm_bn >= eofs) {
553  		xfs_alert(btp->bt_mount,
554  			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
555  			  __func__, cmap.bm_bn, eofs);
556  		WARN_ON(1);
557  		return -EFSCORRUPTED;
558  	}
559  
560  	pag = xfs_perag_get(btp->bt_mount,
561  			    xfs_daddr_to_agno(btp->bt_mount, cmap.bm_bn));
562  
563  	spin_lock(&pag->pag_buf_lock);
564  	bp = rhashtable_lookup_fast(&pag->pag_buf_hash, &cmap,
565  				    xfs_buf_hash_params);
566  	if (bp) {
567  		atomic_inc(&bp->b_hold);
568  		goto found;
569  	}
570  
571  	/* No match found */
572  	if (!new_bp) {
573  		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
574  		spin_unlock(&pag->pag_buf_lock);
575  		xfs_perag_put(pag);
576  		return -ENOENT;
577  	}
578  
579  	/* the buffer keeps the perag reference until it is freed */
580  	new_bp->b_pag = pag;
581  	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,
582  			       xfs_buf_hash_params);
583  	spin_unlock(&pag->pag_buf_lock);
584  	*found_bp = new_bp;
585  	return 0;
586  
587  found:
588  	spin_unlock(&pag->pag_buf_lock);
589  	xfs_perag_put(pag);
590  
591  	if (!xfs_buf_trylock(bp)) {
592  		if (flags & XBF_TRYLOCK) {
593  			xfs_buf_rele(bp);
594  			XFS_STATS_INC(btp->bt_mount, xb_busy_locked);
595  			return -EAGAIN;
596  		}
597  		xfs_buf_lock(bp);
598  		XFS_STATS_INC(btp->bt_mount, xb_get_locked_waited);
599  	}
600  
601  	/*
602  	 * if the buffer is stale, clear all the external state associated with
603  	 * it. We need to keep flags such as how we allocated the buffer memory
604  	 * intact here.
605  	 */
606  	if (bp->b_flags & XBF_STALE) {
607  		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
608  		bp->b_flags &= _XBF_KMEM | _XBF_PAGES;
609  		bp->b_ops = NULL;
610  	}
611  
612  	trace_xfs_buf_find(bp, flags, _RET_IP_);
613  	XFS_STATS_INC(btp->bt_mount, xb_get_locked);
614  	*found_bp = bp;
615  	return 0;
616  }
617  
618  struct xfs_buf *
619  xfs_buf_incore(
620  	struct xfs_buftarg	*target,
621  	xfs_daddr_t		blkno,
622  	size_t			numblks,
623  	xfs_buf_flags_t		flags)
624  {
625  	struct xfs_buf		*bp;
626  	int			error;
627  	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
628  
629  	error = xfs_buf_find(target, &map, 1, flags, NULL, &bp);
630  	if (error)
631  		return NULL;
632  	return bp;
633  }
634  
635  /*
636   * Assembles a buffer covering the specified range. The code is optimised for
637   * cache hits, as metadata intensive workloads will see 3 orders of magnitude
638   * more hits than misses.
639   */
640  int
641  xfs_buf_get_map(
642  	struct xfs_buftarg	*target,
643  	struct xfs_buf_map	*map,
644  	int			nmaps,
645  	xfs_buf_flags_t		flags,
646  	struct xfs_buf		**bpp)
647  {
648  	struct xfs_buf		*bp;
649  	struct xfs_buf		*new_bp;
650  	int			error;
651  
652  	*bpp = NULL;
653  	error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp);
654  	if (!error)
655  		goto found;
656  	if (error != -ENOENT)
657  		return error;
658  
659  	error = _xfs_buf_alloc(target, map, nmaps, flags, &new_bp);
660  	if (error)
661  		return error;
662  
663  	/*
664  	 * For buffers that fit entirely within a single page, first attempt to
665  	 * allocate the memory from the heap to minimise memory usage. If we
666  	 * can't get heap memory for these small buffers, we fall back to using
667  	 * the page allocator.
668  	 */
669  	if (BBTOB(new_bp->b_length) >= PAGE_SIZE ||
670  	    xfs_buf_alloc_kmem(new_bp, flags) < 0) {
671  		error = xfs_buf_alloc_pages(new_bp, flags);
672  		if (error)
673  			goto out_free_buf;
674  	}
675  
676  	error = xfs_buf_find(target, map, nmaps, flags, new_bp, &bp);
677  	if (error)
678  		goto out_free_buf;
679  
680  	if (bp != new_bp)
681  		xfs_buf_free(new_bp);
682  
683  found:
684  	if (!bp->b_addr) {
685  		error = _xfs_buf_map_pages(bp, flags);
686  		if (unlikely(error)) {
687  			xfs_warn_ratelimited(target->bt_mount,
688  				"%s: failed to map %u pages", __func__,
689  				bp->b_page_count);
690  			xfs_buf_relse(bp);
691  			return error;
692  		}
693  	}
694  
695  	/*
696  	 * Clear b_error if this is a lookup from a caller that doesn't expect
697  	 * valid data to be found in the buffer.
698  	 */
699  	if (!(flags & XBF_READ))
700  		xfs_buf_ioerror(bp, 0);
701  
702  	XFS_STATS_INC(target->bt_mount, xb_get);
703  	trace_xfs_buf_get(bp, flags, _RET_IP_);
704  	*bpp = bp;
705  	return 0;
706  out_free_buf:
707  	xfs_buf_free(new_bp);
708  	return error;
709  }
710  
711  int
712  _xfs_buf_read(
713  	struct xfs_buf		*bp,
714  	xfs_buf_flags_t		flags)
715  {
716  	ASSERT(!(flags & XBF_WRITE));
717  	ASSERT(bp->b_maps[0].bm_bn != XFS_BUF_DADDR_NULL);
718  
719  	bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD | XBF_DONE);
720  	bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
721  
722  	return xfs_buf_submit(bp);
723  }
724  
725  /*
726   * Reverify a buffer found in cache without an attached ->b_ops.
727   *
728   * If the caller passed an ops structure and the buffer doesn't have ops
729   * assigned, set the ops and use it to verify the contents. If verification
730   * fails, clear XBF_DONE. We assume the buffer has no recorded errors and is
731   * already in XBF_DONE state on entry.
732   *
733   * Under normal operations, every in-core buffer is verified on read I/O
734   * completion. There are two scenarios that can lead to in-core buffers without
735   * an assigned ->b_ops. The first is during log recovery of buffers on a V4
736   * filesystem, though these buffers are purged at the end of recovery. The
737   * other is online repair, which intentionally reads with a NULL buffer ops to
738   * run several verifiers across an in-core buffer in order to establish buffer
739   * type.  If repair can't establish that, the buffer will be left in memory
740   * with NULL buffer ops.
741   */
742  int
743  xfs_buf_reverify(
744  	struct xfs_buf		*bp,
745  	const struct xfs_buf_ops *ops)
746  {
747  	ASSERT(bp->b_flags & XBF_DONE);
748  	ASSERT(bp->b_error == 0);
749  
750  	if (!ops || bp->b_ops)
751  		return 0;
752  
753  	bp->b_ops = ops;
754  	bp->b_ops->verify_read(bp);
755  	if (bp->b_error)
756  		bp->b_flags &= ~XBF_DONE;
757  	return bp->b_error;
758  }
759  
760  int
761  xfs_buf_read_map(
762  	struct xfs_buftarg	*target,
763  	struct xfs_buf_map	*map,
764  	int			nmaps,
765  	xfs_buf_flags_t		flags,
766  	struct xfs_buf		**bpp,
767  	const struct xfs_buf_ops *ops,
768  	xfs_failaddr_t		fa)
769  {
770  	struct xfs_buf		*bp;
771  	int			error;
772  
773  	flags |= XBF_READ;
774  	*bpp = NULL;
775  
776  	error = xfs_buf_get_map(target, map, nmaps, flags, &bp);
777  	if (error)
778  		return error;
779  
780  	trace_xfs_buf_read(bp, flags, _RET_IP_);
781  
782  	if (!(bp->b_flags & XBF_DONE)) {
783  		/* Initiate the buffer read and wait. */
784  		XFS_STATS_INC(target->bt_mount, xb_get_read);
785  		bp->b_ops = ops;
786  		error = _xfs_buf_read(bp, flags);
787  
788  		/* Readahead iodone already dropped the buffer, so exit. */
789  		if (flags & XBF_ASYNC)
790  			return 0;
791  	} else {
792  		/* Buffer already read; all we need to do is check it. */
793  		error = xfs_buf_reverify(bp, ops);
794  
795  		/* Readahead already finished; drop the buffer and exit. */
796  		if (flags & XBF_ASYNC) {
797  			xfs_buf_relse(bp);
798  			return 0;
799  		}
800  
801  		/* We do not want read in the flags */
802  		bp->b_flags &= ~XBF_READ;
803  		ASSERT(bp->b_ops != NULL || ops == NULL);
804  	}
805  
806  	/*
807  	 * If we've had a read error, then the contents of the buffer are
808  	 * invalid and should not be used. To ensure that a followup read tries
809  	 * to pull the buffer from disk again, we clear the XBF_DONE flag and
810  	 * mark the buffer stale. This ensures that anyone who has a current
811  	 * reference to the buffer will interpret it's contents correctly and
812  	 * future cache lookups will also treat it as an empty, uninitialised
813  	 * buffer.
814  	 */
815  	if (error) {
816  		if (!xfs_is_shutdown(target->bt_mount))
817  			xfs_buf_ioerror_alert(bp, fa);
818  
819  		bp->b_flags &= ~XBF_DONE;
820  		xfs_buf_stale(bp);
821  		xfs_buf_relse(bp);
822  
823  		/* bad CRC means corrupted metadata */
824  		if (error == -EFSBADCRC)
825  			error = -EFSCORRUPTED;
826  		return error;
827  	}
828  
829  	*bpp = bp;
830  	return 0;
831  }
832  
833  /*
834   *	If we are not low on memory then do the readahead in a deadlock
835   *	safe manner.
836   */
837  void
838  xfs_buf_readahead_map(
839  	struct xfs_buftarg	*target,
840  	struct xfs_buf_map	*map,
841  	int			nmaps,
842  	const struct xfs_buf_ops *ops)
843  {
844  	struct xfs_buf		*bp;
845  
846  	if (bdi_read_congested(target->bt_bdev->bd_disk->bdi))
847  		return;
848  
849  	xfs_buf_read_map(target, map, nmaps,
850  		     XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD, &bp, ops,
851  		     __this_address);
852  }
853  
854  /*
855   * Read an uncached buffer from disk. Allocates and returns a locked
856   * buffer containing the disk contents or nothing. Uncached buffers always have
857   * a cache index of XFS_BUF_DADDR_NULL so we can easily determine if the buffer
858   * is cached or uncached during fault diagnosis.
859   */
860  int
861  xfs_buf_read_uncached(
862  	struct xfs_buftarg	*target,
863  	xfs_daddr_t		daddr,
864  	size_t			numblks,
865  	int			flags,
866  	struct xfs_buf		**bpp,
867  	const struct xfs_buf_ops *ops)
868  {
869  	struct xfs_buf		*bp;
870  	int			error;
871  
872  	*bpp = NULL;
873  
874  	error = xfs_buf_get_uncached(target, numblks, flags, &bp);
875  	if (error)
876  		return error;
877  
878  	/* set up the buffer for a read IO */
879  	ASSERT(bp->b_map_count == 1);
880  	bp->b_rhash_key = XFS_BUF_DADDR_NULL;
881  	bp->b_maps[0].bm_bn = daddr;
882  	bp->b_flags |= XBF_READ;
883  	bp->b_ops = ops;
884  
885  	xfs_buf_submit(bp);
886  	if (bp->b_error) {
887  		error = bp->b_error;
888  		xfs_buf_relse(bp);
889  		return error;
890  	}
891  
892  	*bpp = bp;
893  	return 0;
894  }
895  
896  int
897  xfs_buf_get_uncached(
898  	struct xfs_buftarg	*target,
899  	size_t			numblks,
900  	int			flags,
901  	struct xfs_buf		**bpp)
902  {
903  	int			error;
904  	struct xfs_buf		*bp;
905  	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
906  
907  	*bpp = NULL;
908  
909  	/* flags might contain irrelevant bits, pass only what we care about */
910  	error = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT, &bp);
911  	if (error)
912  		return error;
913  
914  	error = xfs_buf_alloc_pages(bp, flags);
915  	if (error)
916  		goto fail_free_buf;
917  
918  	error = _xfs_buf_map_pages(bp, 0);
919  	if (unlikely(error)) {
920  		xfs_warn(target->bt_mount,
921  			"%s: failed to map pages", __func__);
922  		goto fail_free_buf;
923  	}
924  
925  	trace_xfs_buf_get_uncached(bp, _RET_IP_);
926  	*bpp = bp;
927  	return 0;
928  
929  fail_free_buf:
930  	xfs_buf_free(bp);
931  	return error;
932  }
933  
934  /*
935   *	Increment reference count on buffer, to hold the buffer concurrently
936   *	with another thread which may release (free) the buffer asynchronously.
937   *	Must hold the buffer already to call this function.
938   */
939  void
940  xfs_buf_hold(
941  	struct xfs_buf		*bp)
942  {
943  	trace_xfs_buf_hold(bp, _RET_IP_);
944  	atomic_inc(&bp->b_hold);
945  }
946  
947  /*
948   * Release a hold on the specified buffer. If the hold count is 1, the buffer is
949   * placed on LRU or freed (depending on b_lru_ref).
950   */
951  void
952  xfs_buf_rele(
953  	struct xfs_buf		*bp)
954  {
955  	struct xfs_perag	*pag = bp->b_pag;
956  	bool			release;
957  	bool			freebuf = false;
958  
959  	trace_xfs_buf_rele(bp, _RET_IP_);
960  
961  	if (!pag) {
962  		ASSERT(list_empty(&bp->b_lru));
963  		if (atomic_dec_and_test(&bp->b_hold)) {
964  			xfs_buf_ioacct_dec(bp);
965  			xfs_buf_free(bp);
966  		}
967  		return;
968  	}
969  
970  	ASSERT(atomic_read(&bp->b_hold) > 0);
971  
972  	/*
973  	 * We grab the b_lock here first to serialise racing xfs_buf_rele()
974  	 * calls. The pag_buf_lock being taken on the last reference only
975  	 * serialises against racing lookups in xfs_buf_find(). IOWs, the second
976  	 * to last reference we drop here is not serialised against the last
977  	 * reference until we take bp->b_lock. Hence if we don't grab b_lock
978  	 * first, the last "release" reference can win the race to the lock and
979  	 * free the buffer before the second-to-last reference is processed,
980  	 * leading to a use-after-free scenario.
981  	 */
982  	spin_lock(&bp->b_lock);
983  	release = atomic_dec_and_lock(&bp->b_hold, &pag->pag_buf_lock);
984  	if (!release) {
985  		/*
986  		 * Drop the in-flight state if the buffer is already on the LRU
987  		 * and it holds the only reference. This is racy because we
988  		 * haven't acquired the pag lock, but the use of _XBF_IN_FLIGHT
989  		 * ensures the decrement occurs only once per-buf.
990  		 */
991  		if ((atomic_read(&bp->b_hold) == 1) && !list_empty(&bp->b_lru))
992  			__xfs_buf_ioacct_dec(bp);
993  		goto out_unlock;
994  	}
995  
996  	/* the last reference has been dropped ... */
997  	__xfs_buf_ioacct_dec(bp);
998  	if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) {
999  		/*
1000  		 * If the buffer is added to the LRU take a new reference to the
1001  		 * buffer for the LRU and clear the (now stale) dispose list
1002  		 * state flag
1003  		 */
1004  		if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) {
1005  			bp->b_state &= ~XFS_BSTATE_DISPOSE;
1006  			atomic_inc(&bp->b_hold);
1007  		}
1008  		spin_unlock(&pag->pag_buf_lock);
1009  	} else {
1010  		/*
1011  		 * most of the time buffers will already be removed from the
1012  		 * LRU, so optimise that case by checking for the
1013  		 * XFS_BSTATE_DISPOSE flag indicating the last list the buffer
1014  		 * was on was the disposal list
1015  		 */
1016  		if (!(bp->b_state & XFS_BSTATE_DISPOSE)) {
1017  			list_lru_del(&bp->b_target->bt_lru, &bp->b_lru);
1018  		} else {
1019  			ASSERT(list_empty(&bp->b_lru));
1020  		}
1021  
1022  		ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
1023  		rhashtable_remove_fast(&pag->pag_buf_hash, &bp->b_rhash_head,
1024  				       xfs_buf_hash_params);
1025  		spin_unlock(&pag->pag_buf_lock);
1026  		xfs_perag_put(pag);
1027  		freebuf = true;
1028  	}
1029  
1030  out_unlock:
1031  	spin_unlock(&bp->b_lock);
1032  
1033  	if (freebuf)
1034  		xfs_buf_free(bp);
1035  }
1036  
1037  
1038  /*
1039   *	Lock a buffer object, if it is not already locked.
1040   *
1041   *	If we come across a stale, pinned, locked buffer, we know that we are
1042   *	being asked to lock a buffer that has been reallocated. Because it is
1043   *	pinned, we know that the log has not been pushed to disk and hence it
1044   *	will still be locked.  Rather than continuing to have trylock attempts
1045   *	fail until someone else pushes the log, push it ourselves before
1046   *	returning.  This means that the xfsaild will not get stuck trying
1047   *	to push on stale inode buffers.
1048   */
1049  int
1050  xfs_buf_trylock(
1051  	struct xfs_buf		*bp)
1052  {
1053  	int			locked;
1054  
1055  	locked = down_trylock(&bp->b_sema) == 0;
1056  	if (locked)
1057  		trace_xfs_buf_trylock(bp, _RET_IP_);
1058  	else
1059  		trace_xfs_buf_trylock_fail(bp, _RET_IP_);
1060  	return locked;
1061  }
1062  
1063  /*
1064   *	Lock a buffer object.
1065   *
1066   *	If we come across a stale, pinned, locked buffer, we know that we
1067   *	are being asked to lock a buffer that has been reallocated. Because
1068   *	it is pinned, we know that the log has not been pushed to disk and
1069   *	hence it will still be locked. Rather than sleeping until someone
1070   *	else pushes the log, push it ourselves before trying to get the lock.
1071   */
1072  void
1073  xfs_buf_lock(
1074  	struct xfs_buf		*bp)
1075  {
1076  	trace_xfs_buf_lock(bp, _RET_IP_);
1077  
1078  	if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
1079  		xfs_log_force(bp->b_mount, 0);
1080  	down(&bp->b_sema);
1081  
1082  	trace_xfs_buf_lock_done(bp, _RET_IP_);
1083  }
1084  
1085  void
1086  xfs_buf_unlock(
1087  	struct xfs_buf		*bp)
1088  {
1089  	ASSERT(xfs_buf_islocked(bp));
1090  
1091  	up(&bp->b_sema);
1092  	trace_xfs_buf_unlock(bp, _RET_IP_);
1093  }
1094  
1095  STATIC void
1096  xfs_buf_wait_unpin(
1097  	struct xfs_buf		*bp)
1098  {
1099  	DECLARE_WAITQUEUE	(wait, current);
1100  
1101  	if (atomic_read(&bp->b_pin_count) == 0)
1102  		return;
1103  
1104  	add_wait_queue(&bp->b_waiters, &wait);
1105  	for (;;) {
1106  		set_current_state(TASK_UNINTERRUPTIBLE);
1107  		if (atomic_read(&bp->b_pin_count) == 0)
1108  			break;
1109  		io_schedule();
1110  	}
1111  	remove_wait_queue(&bp->b_waiters, &wait);
1112  	set_current_state(TASK_RUNNING);
1113  }
1114  
1115  static void
1116  xfs_buf_ioerror_alert_ratelimited(
1117  	struct xfs_buf		*bp)
1118  {
1119  	static unsigned long	lasttime;
1120  	static struct xfs_buftarg *lasttarg;
1121  
1122  	if (bp->b_target != lasttarg ||
1123  	    time_after(jiffies, (lasttime + 5*HZ))) {
1124  		lasttime = jiffies;
1125  		xfs_buf_ioerror_alert(bp, __this_address);
1126  	}
1127  	lasttarg = bp->b_target;
1128  }
1129  
1130  /*
1131   * Account for this latest trip around the retry handler, and decide if
1132   * we've failed enough times to constitute a permanent failure.
1133   */
1134  static bool
1135  xfs_buf_ioerror_permanent(
1136  	struct xfs_buf		*bp,
1137  	struct xfs_error_cfg	*cfg)
1138  {
1139  	struct xfs_mount	*mp = bp->b_mount;
1140  
1141  	if (cfg->max_retries != XFS_ERR_RETRY_FOREVER &&
1142  	    ++bp->b_retries > cfg->max_retries)
1143  		return true;
1144  	if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
1145  	    time_after(jiffies, cfg->retry_timeout + bp->b_first_retry_time))
1146  		return true;
1147  
1148  	/* At unmount we may treat errors differently */
1149  	if (xfs_is_unmounting(mp) && mp->m_fail_unmount)
1150  		return true;
1151  
1152  	return false;
1153  }
1154  
1155  /*
1156   * On a sync write or shutdown we just want to stale the buffer and let the
1157   * caller handle the error in bp->b_error appropriately.
1158   *
1159   * If the write was asynchronous then no one will be looking for the error.  If
1160   * this is the first failure of this type, clear the error state and write the
1161   * buffer out again. This means we always retry an async write failure at least
1162   * once, but we also need to set the buffer up to behave correctly now for
1163   * repeated failures.
1164   *
1165   * If we get repeated async write failures, then we take action according to the
1166   * error configuration we have been set up to use.
1167   *
1168   * Returns true if this function took care of error handling and the caller must
1169   * not touch the buffer again.  Return false if the caller should proceed with
1170   * normal I/O completion handling.
1171   */
1172  static bool
1173  xfs_buf_ioend_handle_error(
1174  	struct xfs_buf		*bp)
1175  {
1176  	struct xfs_mount	*mp = bp->b_mount;
1177  	struct xfs_error_cfg	*cfg;
1178  
1179  	/*
1180  	 * If we've already decided to shutdown the filesystem because of I/O
1181  	 * errors, there's no point in giving this a retry.
1182  	 */
1183  	if (xfs_is_shutdown(mp))
1184  		goto out_stale;
1185  
1186  	xfs_buf_ioerror_alert_ratelimited(bp);
1187  
1188  	/*
1189  	 * We're not going to bother about retrying this during recovery.
1190  	 * One strike!
1191  	 */
1192  	if (bp->b_flags & _XBF_LOGRECOVERY) {
1193  		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
1194  		return false;
1195  	}
1196  
1197  	/*
1198  	 * Synchronous writes will have callers process the error.
1199  	 */
1200  	if (!(bp->b_flags & XBF_ASYNC))
1201  		goto out_stale;
1202  
1203  	trace_xfs_buf_iodone_async(bp, _RET_IP_);
1204  
1205  	cfg = xfs_error_get_cfg(mp, XFS_ERR_METADATA, bp->b_error);
1206  	if (bp->b_last_error != bp->b_error ||
1207  	    !(bp->b_flags & (XBF_STALE | XBF_WRITE_FAIL))) {
1208  		bp->b_last_error = bp->b_error;
1209  		if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
1210  		    !bp->b_first_retry_time)
1211  			bp->b_first_retry_time = jiffies;
1212  		goto resubmit;
1213  	}
1214  
1215  	/*
1216  	 * Permanent error - we need to trigger a shutdown if we haven't already
1217  	 * to indicate that inconsistency will result from this action.
1218  	 */
1219  	if (xfs_buf_ioerror_permanent(bp, cfg)) {
1220  		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
1221  		goto out_stale;
1222  	}
1223  
1224  	/* Still considered a transient error. Caller will schedule retries. */
1225  	if (bp->b_flags & _XBF_INODES)
1226  		xfs_buf_inode_io_fail(bp);
1227  	else if (bp->b_flags & _XBF_DQUOTS)
1228  		xfs_buf_dquot_io_fail(bp);
1229  	else
1230  		ASSERT(list_empty(&bp->b_li_list));
1231  	xfs_buf_ioerror(bp, 0);
1232  	xfs_buf_relse(bp);
1233  	return true;
1234  
1235  resubmit:
1236  	xfs_buf_ioerror(bp, 0);
1237  	bp->b_flags |= (XBF_DONE | XBF_WRITE_FAIL);
1238  	xfs_buf_submit(bp);
1239  	return true;
1240  out_stale:
1241  	xfs_buf_stale(bp);
1242  	bp->b_flags |= XBF_DONE;
1243  	bp->b_flags &= ~XBF_WRITE;
1244  	trace_xfs_buf_error_relse(bp, _RET_IP_);
1245  	return false;
1246  }
1247  
1248  static void
1249  xfs_buf_ioend(
1250  	struct xfs_buf	*bp)
1251  {
1252  	trace_xfs_buf_iodone(bp, _RET_IP_);
1253  
1254  	/*
1255  	 * Pull in IO completion errors now. We are guaranteed to be running
1256  	 * single threaded, so we don't need the lock to read b_io_error.
1257  	 */
1258  	if (!bp->b_error && bp->b_io_error)
1259  		xfs_buf_ioerror(bp, bp->b_io_error);
1260  
1261  	if (bp->b_flags & XBF_READ) {
1262  		if (!bp->b_error && bp->b_ops)
1263  			bp->b_ops->verify_read(bp);
1264  		if (!bp->b_error)
1265  			bp->b_flags |= XBF_DONE;
1266  	} else {
1267  		if (!bp->b_error) {
1268  			bp->b_flags &= ~XBF_WRITE_FAIL;
1269  			bp->b_flags |= XBF_DONE;
1270  		}
1271  
1272  		if (unlikely(bp->b_error) && xfs_buf_ioend_handle_error(bp))
1273  			return;
1274  
1275  		/* clear the retry state */
1276  		bp->b_last_error = 0;
1277  		bp->b_retries = 0;
1278  		bp->b_first_retry_time = 0;
1279  
1280  		/*
1281  		 * Note that for things like remote attribute buffers, there may
1282  		 * not be a buffer log item here, so processing the buffer log
1283  		 * item must remain optional.
1284  		 */
1285  		if (bp->b_log_item)
1286  			xfs_buf_item_done(bp);
1287  
1288  		if (bp->b_flags & _XBF_INODES)
1289  			xfs_buf_inode_iodone(bp);
1290  		else if (bp->b_flags & _XBF_DQUOTS)
1291  			xfs_buf_dquot_iodone(bp);
1292  
1293  	}
1294  
1295  	bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD |
1296  			 _XBF_LOGRECOVERY);
1297  
1298  	if (bp->b_flags & XBF_ASYNC)
1299  		xfs_buf_relse(bp);
1300  	else
1301  		complete(&bp->b_iowait);
1302  }
1303  
1304  static void
1305  xfs_buf_ioend_work(
1306  	struct work_struct	*work)
1307  {
1308  	struct xfs_buf		*bp =
1309  		container_of(work, struct xfs_buf, b_ioend_work);
1310  
1311  	xfs_buf_ioend(bp);
1312  }
1313  
1314  static void
1315  xfs_buf_ioend_async(
1316  	struct xfs_buf	*bp)
1317  {
1318  	INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
1319  	queue_work(bp->b_mount->m_buf_workqueue, &bp->b_ioend_work);
1320  }
1321  
1322  void
1323  __xfs_buf_ioerror(
1324  	struct xfs_buf		*bp,
1325  	int			error,
1326  	xfs_failaddr_t		failaddr)
1327  {
1328  	ASSERT(error <= 0 && error >= -1000);
1329  	bp->b_error = error;
1330  	trace_xfs_buf_ioerror(bp, error, failaddr);
1331  }
1332  
1333  void
1334  xfs_buf_ioerror_alert(
1335  	struct xfs_buf		*bp,
1336  	xfs_failaddr_t		func)
1337  {
1338  	xfs_buf_alert_ratelimited(bp, "XFS: metadata IO error",
1339  		"metadata I/O error in \"%pS\" at daddr 0x%llx len %d error %d",
1340  				  func, (uint64_t)xfs_buf_daddr(bp),
1341  				  bp->b_length, -bp->b_error);
1342  }
1343  
1344  /*
1345   * To simulate an I/O failure, the buffer must be locked and held with at least
1346   * three references. The LRU reference is dropped by the stale call. The buf
1347   * item reference is dropped via ioend processing. The third reference is owned
1348   * by the caller and is dropped on I/O completion if the buffer is XBF_ASYNC.
1349   */
1350  void
1351  xfs_buf_ioend_fail(
1352  	struct xfs_buf	*bp)
1353  {
1354  	bp->b_flags &= ~XBF_DONE;
1355  	xfs_buf_stale(bp);
1356  	xfs_buf_ioerror(bp, -EIO);
1357  	xfs_buf_ioend(bp);
1358  }
1359  
1360  int
1361  xfs_bwrite(
1362  	struct xfs_buf		*bp)
1363  {
1364  	int			error;
1365  
1366  	ASSERT(xfs_buf_islocked(bp));
1367  
1368  	bp->b_flags |= XBF_WRITE;
1369  	bp->b_flags &= ~(XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q |
1370  			 XBF_DONE);
1371  
1372  	error = xfs_buf_submit(bp);
1373  	if (error)
1374  		xfs_force_shutdown(bp->b_mount, SHUTDOWN_META_IO_ERROR);
1375  	return error;
1376  }
1377  
1378  static void
1379  xfs_buf_bio_end_io(
1380  	struct bio		*bio)
1381  {
1382  	struct xfs_buf		*bp = (struct xfs_buf *)bio->bi_private;
1383  
1384  	if (!bio->bi_status &&
1385  	    (bp->b_flags & XBF_WRITE) && (bp->b_flags & XBF_ASYNC) &&
1386  	    XFS_TEST_ERROR(false, bp->b_mount, XFS_ERRTAG_BUF_IOERROR))
1387  		bio->bi_status = BLK_STS_IOERR;
1388  
1389  	/*
1390  	 * don't overwrite existing errors - otherwise we can lose errors on
1391  	 * buffers that require multiple bios to complete.
1392  	 */
1393  	if (bio->bi_status) {
1394  		int error = blk_status_to_errno(bio->bi_status);
1395  
1396  		cmpxchg(&bp->b_io_error, 0, error);
1397  	}
1398  
1399  	if (!bp->b_error && xfs_buf_is_vmapped(bp) && (bp->b_flags & XBF_READ))
1400  		invalidate_kernel_vmap_range(bp->b_addr, xfs_buf_vmap_len(bp));
1401  
1402  	if (atomic_dec_and_test(&bp->b_io_remaining) == 1)
1403  		xfs_buf_ioend_async(bp);
1404  	bio_put(bio);
1405  }
1406  
1407  static void
1408  xfs_buf_ioapply_map(
1409  	struct xfs_buf	*bp,
1410  	int		map,
1411  	int		*buf_offset,
1412  	int		*count,
1413  	int		op)
1414  {
1415  	int		page_index;
1416  	unsigned int	total_nr_pages = bp->b_page_count;
1417  	int		nr_pages;
1418  	struct bio	*bio;
1419  	sector_t	sector =  bp->b_maps[map].bm_bn;
1420  	int		size;
1421  	int		offset;
1422  
1423  	/* skip the pages in the buffer before the start offset */
1424  	page_index = 0;
1425  	offset = *buf_offset;
1426  	while (offset >= PAGE_SIZE) {
1427  		page_index++;
1428  		offset -= PAGE_SIZE;
1429  	}
1430  
1431  	/*
1432  	 * Limit the IO size to the length of the current vector, and update the
1433  	 * remaining IO count for the next time around.
1434  	 */
1435  	size = min_t(int, BBTOB(bp->b_maps[map].bm_len), *count);
1436  	*count -= size;
1437  	*buf_offset += size;
1438  
1439  next_chunk:
1440  	atomic_inc(&bp->b_io_remaining);
1441  	nr_pages = bio_max_segs(total_nr_pages);
1442  
1443  	bio = bio_alloc(GFP_NOIO, nr_pages);
1444  	bio_set_dev(bio, bp->b_target->bt_bdev);
1445  	bio->bi_iter.bi_sector = sector;
1446  	bio->bi_end_io = xfs_buf_bio_end_io;
1447  	bio->bi_private = bp;
1448  	bio->bi_opf = op;
1449  
1450  	for (; size && nr_pages; nr_pages--, page_index++) {
1451  		int	rbytes, nbytes = PAGE_SIZE - offset;
1452  
1453  		if (nbytes > size)
1454  			nbytes = size;
1455  
1456  		rbytes = bio_add_page(bio, bp->b_pages[page_index], nbytes,
1457  				      offset);
1458  		if (rbytes < nbytes)
1459  			break;
1460  
1461  		offset = 0;
1462  		sector += BTOBB(nbytes);
1463  		size -= nbytes;
1464  		total_nr_pages--;
1465  	}
1466  
1467  	if (likely(bio->bi_iter.bi_size)) {
1468  		if (xfs_buf_is_vmapped(bp)) {
1469  			flush_kernel_vmap_range(bp->b_addr,
1470  						xfs_buf_vmap_len(bp));
1471  		}
1472  		submit_bio(bio);
1473  		if (size)
1474  			goto next_chunk;
1475  	} else {
1476  		/*
1477  		 * This is guaranteed not to be the last io reference count
1478  		 * because the caller (xfs_buf_submit) holds a count itself.
1479  		 */
1480  		atomic_dec(&bp->b_io_remaining);
1481  		xfs_buf_ioerror(bp, -EIO);
1482  		bio_put(bio);
1483  	}
1484  
1485  }
1486  
1487  STATIC void
1488  _xfs_buf_ioapply(
1489  	struct xfs_buf	*bp)
1490  {
1491  	struct blk_plug	plug;
1492  	int		op;
1493  	int		offset;
1494  	int		size;
1495  	int		i;
1496  
1497  	/*
1498  	 * Make sure we capture only current IO errors rather than stale errors
1499  	 * left over from previous use of the buffer (e.g. failed readahead).
1500  	 */
1501  	bp->b_error = 0;
1502  
1503  	if (bp->b_flags & XBF_WRITE) {
1504  		op = REQ_OP_WRITE;
1505  
1506  		/*
1507  		 * Run the write verifier callback function if it exists. If
1508  		 * this function fails it will mark the buffer with an error and
1509  		 * the IO should not be dispatched.
1510  		 */
1511  		if (bp->b_ops) {
1512  			bp->b_ops->verify_write(bp);
1513  			if (bp->b_error) {
1514  				xfs_force_shutdown(bp->b_mount,
1515  						   SHUTDOWN_CORRUPT_INCORE);
1516  				return;
1517  			}
1518  		} else if (bp->b_rhash_key != XFS_BUF_DADDR_NULL) {
1519  			struct xfs_mount *mp = bp->b_mount;
1520  
1521  			/*
1522  			 * non-crc filesystems don't attach verifiers during
1523  			 * log recovery, so don't warn for such filesystems.
1524  			 */
1525  			if (xfs_has_crc(mp)) {
1526  				xfs_warn(mp,
1527  					"%s: no buf ops on daddr 0x%llx len %d",
1528  					__func__, xfs_buf_daddr(bp),
1529  					bp->b_length);
1530  				xfs_hex_dump(bp->b_addr,
1531  						XFS_CORRUPTION_DUMP_LEN);
1532  				dump_stack();
1533  			}
1534  		}
1535  	} else {
1536  		op = REQ_OP_READ;
1537  		if (bp->b_flags & XBF_READ_AHEAD)
1538  			op |= REQ_RAHEAD;
1539  	}
1540  
1541  	/* we only use the buffer cache for meta-data */
1542  	op |= REQ_META;
1543  
1544  	/*
1545  	 * Walk all the vectors issuing IO on them. Set up the initial offset
1546  	 * into the buffer and the desired IO size before we start -
1547  	 * _xfs_buf_ioapply_vec() will modify them appropriately for each
1548  	 * subsequent call.
1549  	 */
1550  	offset = bp->b_offset;
1551  	size = BBTOB(bp->b_length);
1552  	blk_start_plug(&plug);
1553  	for (i = 0; i < bp->b_map_count; i++) {
1554  		xfs_buf_ioapply_map(bp, i, &offset, &size, op);
1555  		if (bp->b_error)
1556  			break;
1557  		if (size <= 0)
1558  			break;	/* all done */
1559  	}
1560  	blk_finish_plug(&plug);
1561  }
1562  
1563  /*
1564   * Wait for I/O completion of a sync buffer and return the I/O error code.
1565   */
1566  static int
1567  xfs_buf_iowait(
1568  	struct xfs_buf	*bp)
1569  {
1570  	ASSERT(!(bp->b_flags & XBF_ASYNC));
1571  
1572  	trace_xfs_buf_iowait(bp, _RET_IP_);
1573  	wait_for_completion(&bp->b_iowait);
1574  	trace_xfs_buf_iowait_done(bp, _RET_IP_);
1575  
1576  	return bp->b_error;
1577  }
1578  
1579  /*
1580   * Buffer I/O submission path, read or write. Asynchronous submission transfers
1581   * the buffer lock ownership and the current reference to the IO. It is not
1582   * safe to reference the buffer after a call to this function unless the caller
1583   * holds an additional reference itself.
1584   */
1585  static int
1586  __xfs_buf_submit(
1587  	struct xfs_buf	*bp,
1588  	bool		wait)
1589  {
1590  	int		error = 0;
1591  
1592  	trace_xfs_buf_submit(bp, _RET_IP_);
1593  
1594  	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
1595  
1596  	/* on shutdown we stale and complete the buffer immediately */
1597  	if (xfs_is_shutdown(bp->b_mount)) {
1598  		xfs_buf_ioend_fail(bp);
1599  		return -EIO;
1600  	}
1601  
1602  	/*
1603  	 * Grab a reference so the buffer does not go away underneath us. For
1604  	 * async buffers, I/O completion drops the callers reference, which
1605  	 * could occur before submission returns.
1606  	 */
1607  	xfs_buf_hold(bp);
1608  
1609  	if (bp->b_flags & XBF_WRITE)
1610  		xfs_buf_wait_unpin(bp);
1611  
1612  	/* clear the internal error state to avoid spurious errors */
1613  	bp->b_io_error = 0;
1614  
1615  	/*
1616  	 * Set the count to 1 initially, this will stop an I/O completion
1617  	 * callout which happens before we have started all the I/O from calling
1618  	 * xfs_buf_ioend too early.
1619  	 */
1620  	atomic_set(&bp->b_io_remaining, 1);
1621  	if (bp->b_flags & XBF_ASYNC)
1622  		xfs_buf_ioacct_inc(bp);
1623  	_xfs_buf_ioapply(bp);
1624  
1625  	/*
1626  	 * If _xfs_buf_ioapply failed, we can get back here with only the IO
1627  	 * reference we took above. If we drop it to zero, run completion so
1628  	 * that we don't return to the caller with completion still pending.
1629  	 */
1630  	if (atomic_dec_and_test(&bp->b_io_remaining) == 1) {
1631  		if (bp->b_error || !(bp->b_flags & XBF_ASYNC))
1632  			xfs_buf_ioend(bp);
1633  		else
1634  			xfs_buf_ioend_async(bp);
1635  	}
1636  
1637  	if (wait)
1638  		error = xfs_buf_iowait(bp);
1639  
1640  	/*
1641  	 * Release the hold that keeps the buffer referenced for the entire
1642  	 * I/O. Note that if the buffer is async, it is not safe to reference
1643  	 * after this release.
1644  	 */
1645  	xfs_buf_rele(bp);
1646  	return error;
1647  }
1648  
1649  void *
1650  xfs_buf_offset(
1651  	struct xfs_buf		*bp,
1652  	size_t			offset)
1653  {
1654  	struct page		*page;
1655  
1656  	if (bp->b_addr)
1657  		return bp->b_addr + offset;
1658  
1659  	page = bp->b_pages[offset >> PAGE_SHIFT];
1660  	return page_address(page) + (offset & (PAGE_SIZE-1));
1661  }
1662  
1663  void
1664  xfs_buf_zero(
1665  	struct xfs_buf		*bp,
1666  	size_t			boff,
1667  	size_t			bsize)
1668  {
1669  	size_t			bend;
1670  
1671  	bend = boff + bsize;
1672  	while (boff < bend) {
1673  		struct page	*page;
1674  		int		page_index, page_offset, csize;
1675  
1676  		page_index = (boff + bp->b_offset) >> PAGE_SHIFT;
1677  		page_offset = (boff + bp->b_offset) & ~PAGE_MASK;
1678  		page = bp->b_pages[page_index];
1679  		csize = min_t(size_t, PAGE_SIZE - page_offset,
1680  				      BBTOB(bp->b_length) - boff);
1681  
1682  		ASSERT((csize + page_offset) <= PAGE_SIZE);
1683  
1684  		memset(page_address(page) + page_offset, 0, csize);
1685  
1686  		boff += csize;
1687  	}
1688  }
1689  
1690  /*
1691   * Log a message about and stale a buffer that a caller has decided is corrupt.
1692   *
1693   * This function should be called for the kinds of metadata corruption that
1694   * cannot be detect from a verifier, such as incorrect inter-block relationship
1695   * data.  Do /not/ call this function from a verifier function.
1696   *
1697   * The buffer must be XBF_DONE prior to the call.  Afterwards, the buffer will
1698   * be marked stale, but b_error will not be set.  The caller is responsible for
1699   * releasing the buffer or fixing it.
1700   */
1701  void
1702  __xfs_buf_mark_corrupt(
1703  	struct xfs_buf		*bp,
1704  	xfs_failaddr_t		fa)
1705  {
1706  	ASSERT(bp->b_flags & XBF_DONE);
1707  
1708  	xfs_buf_corruption_error(bp, fa);
1709  	xfs_buf_stale(bp);
1710  }
1711  
1712  /*
1713   *	Handling of buffer targets (buftargs).
1714   */
1715  
1716  /*
1717   * Wait for any bufs with callbacks that have been submitted but have not yet
1718   * returned. These buffers will have an elevated hold count, so wait on those
1719   * while freeing all the buffers only held by the LRU.
1720   */
1721  static enum lru_status
1722  xfs_buftarg_drain_rele(
1723  	struct list_head	*item,
1724  	struct list_lru_one	*lru,
1725  	spinlock_t		*lru_lock,
1726  	void			*arg)
1727  
1728  {
1729  	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
1730  	struct list_head	*dispose = arg;
1731  
1732  	if (atomic_read(&bp->b_hold) > 1) {
1733  		/* need to wait, so skip it this pass */
1734  		trace_xfs_buf_drain_buftarg(bp, _RET_IP_);
1735  		return LRU_SKIP;
1736  	}
1737  	if (!spin_trylock(&bp->b_lock))
1738  		return LRU_SKIP;
1739  
1740  	/*
1741  	 * clear the LRU reference count so the buffer doesn't get
1742  	 * ignored in xfs_buf_rele().
1743  	 */
1744  	atomic_set(&bp->b_lru_ref, 0);
1745  	bp->b_state |= XFS_BSTATE_DISPOSE;
1746  	list_lru_isolate_move(lru, item, dispose);
1747  	spin_unlock(&bp->b_lock);
1748  	return LRU_REMOVED;
1749  }
1750  
1751  /*
1752   * Wait for outstanding I/O on the buftarg to complete.
1753   */
1754  void
1755  xfs_buftarg_wait(
1756  	struct xfs_buftarg	*btp)
1757  {
1758  	/*
1759  	 * First wait on the buftarg I/O count for all in-flight buffers to be
1760  	 * released. This is critical as new buffers do not make the LRU until
1761  	 * they are released.
1762  	 *
1763  	 * Next, flush the buffer workqueue to ensure all completion processing
1764  	 * has finished. Just waiting on buffer locks is not sufficient for
1765  	 * async IO as the reference count held over IO is not released until
1766  	 * after the buffer lock is dropped. Hence we need to ensure here that
1767  	 * all reference counts have been dropped before we start walking the
1768  	 * LRU list.
1769  	 */
1770  	while (percpu_counter_sum(&btp->bt_io_count))
1771  		delay(100);
1772  	flush_workqueue(btp->bt_mount->m_buf_workqueue);
1773  }
1774  
1775  void
1776  xfs_buftarg_drain(
1777  	struct xfs_buftarg	*btp)
1778  {
1779  	LIST_HEAD(dispose);
1780  	int			loop = 0;
1781  	bool			write_fail = false;
1782  
1783  	xfs_buftarg_wait(btp);
1784  
1785  	/* loop until there is nothing left on the lru list. */
1786  	while (list_lru_count(&btp->bt_lru)) {
1787  		list_lru_walk(&btp->bt_lru, xfs_buftarg_drain_rele,
1788  			      &dispose, LONG_MAX);
1789  
1790  		while (!list_empty(&dispose)) {
1791  			struct xfs_buf *bp;
1792  			bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
1793  			list_del_init(&bp->b_lru);
1794  			if (bp->b_flags & XBF_WRITE_FAIL) {
1795  				write_fail = true;
1796  				xfs_buf_alert_ratelimited(bp,
1797  					"XFS: Corruption Alert",
1798  "Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
1799  					(long long)xfs_buf_daddr(bp));
1800  			}
1801  			xfs_buf_rele(bp);
1802  		}
1803  		if (loop++ != 0)
1804  			delay(100);
1805  	}
1806  
1807  	/*
1808  	 * If one or more failed buffers were freed, that means dirty metadata
1809  	 * was thrown away. This should only ever happen after I/O completion
1810  	 * handling has elevated I/O error(s) to permanent failures and shuts
1811  	 * down the fs.
1812  	 */
1813  	if (write_fail) {
1814  		ASSERT(xfs_is_shutdown(btp->bt_mount));
1815  		xfs_alert(btp->bt_mount,
1816  	      "Please run xfs_repair to determine the extent of the problem.");
1817  	}
1818  }
1819  
1820  static enum lru_status
1821  xfs_buftarg_isolate(
1822  	struct list_head	*item,
1823  	struct list_lru_one	*lru,
1824  	spinlock_t		*lru_lock,
1825  	void			*arg)
1826  {
1827  	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
1828  	struct list_head	*dispose = arg;
1829  
1830  	/*
1831  	 * we are inverting the lru lock/bp->b_lock here, so use a trylock.
1832  	 * If we fail to get the lock, just skip it.
1833  	 */
1834  	if (!spin_trylock(&bp->b_lock))
1835  		return LRU_SKIP;
1836  	/*
1837  	 * Decrement the b_lru_ref count unless the value is already
1838  	 * zero. If the value is already zero, we need to reclaim the
1839  	 * buffer, otherwise it gets another trip through the LRU.
1840  	 */
1841  	if (atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
1842  		spin_unlock(&bp->b_lock);
1843  		return LRU_ROTATE;
1844  	}
1845  
1846  	bp->b_state |= XFS_BSTATE_DISPOSE;
1847  	list_lru_isolate_move(lru, item, dispose);
1848  	spin_unlock(&bp->b_lock);
1849  	return LRU_REMOVED;
1850  }
1851  
1852  static unsigned long
1853  xfs_buftarg_shrink_scan(
1854  	struct shrinker		*shrink,
1855  	struct shrink_control	*sc)
1856  {
1857  	struct xfs_buftarg	*btp = container_of(shrink,
1858  					struct xfs_buftarg, bt_shrinker);
1859  	LIST_HEAD(dispose);
1860  	unsigned long		freed;
1861  
1862  	freed = list_lru_shrink_walk(&btp->bt_lru, sc,
1863  				     xfs_buftarg_isolate, &dispose);
1864  
1865  	while (!list_empty(&dispose)) {
1866  		struct xfs_buf *bp;
1867  		bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
1868  		list_del_init(&bp->b_lru);
1869  		xfs_buf_rele(bp);
1870  	}
1871  
1872  	return freed;
1873  }
1874  
1875  static unsigned long
1876  xfs_buftarg_shrink_count(
1877  	struct shrinker		*shrink,
1878  	struct shrink_control	*sc)
1879  {
1880  	struct xfs_buftarg	*btp = container_of(shrink,
1881  					struct xfs_buftarg, bt_shrinker);
1882  	return list_lru_shrink_count(&btp->bt_lru, sc);
1883  }
1884  
1885  void
1886  xfs_free_buftarg(
1887  	struct xfs_buftarg	*btp)
1888  {
1889  	unregister_shrinker(&btp->bt_shrinker);
1890  	ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
1891  	percpu_counter_destroy(&btp->bt_io_count);
1892  	list_lru_destroy(&btp->bt_lru);
1893  
1894  	blkdev_issue_flush(btp->bt_bdev);
1895  
1896  	kmem_free(btp);
1897  }
1898  
1899  int
1900  xfs_setsize_buftarg(
1901  	xfs_buftarg_t		*btp,
1902  	unsigned int		sectorsize)
1903  {
1904  	/* Set up metadata sector size info */
1905  	btp->bt_meta_sectorsize = sectorsize;
1906  	btp->bt_meta_sectormask = sectorsize - 1;
1907  
1908  	if (set_blocksize(btp->bt_bdev, sectorsize)) {
1909  		xfs_warn(btp->bt_mount,
1910  			"Cannot set_blocksize to %u on device %pg",
1911  			sectorsize, btp->bt_bdev);
1912  		return -EINVAL;
1913  	}
1914  
1915  	/* Set up device logical sector size mask */
1916  	btp->bt_logical_sectorsize = bdev_logical_block_size(btp->bt_bdev);
1917  	btp->bt_logical_sectormask = bdev_logical_block_size(btp->bt_bdev) - 1;
1918  
1919  	return 0;
1920  }
1921  
1922  /*
1923   * When allocating the initial buffer target we have not yet
1924   * read in the superblock, so don't know what sized sectors
1925   * are being used at this early stage.  Play safe.
1926   */
1927  STATIC int
1928  xfs_setsize_buftarg_early(
1929  	xfs_buftarg_t		*btp,
1930  	struct block_device	*bdev)
1931  {
1932  	return xfs_setsize_buftarg(btp, bdev_logical_block_size(bdev));
1933  }
1934  
1935  xfs_buftarg_t *
1936  xfs_alloc_buftarg(
1937  	struct xfs_mount	*mp,
1938  	struct block_device	*bdev,
1939  	struct dax_device	*dax_dev)
1940  {
1941  	xfs_buftarg_t		*btp;
1942  
1943  	btp = kmem_zalloc(sizeof(*btp), KM_NOFS);
1944  
1945  	btp->bt_mount = mp;
1946  	btp->bt_dev =  bdev->bd_dev;
1947  	btp->bt_bdev = bdev;
1948  	btp->bt_daxdev = dax_dev;
1949  
1950  	/*
1951  	 * Buffer IO error rate limiting. Limit it to no more than 10 messages
1952  	 * per 30 seconds so as to not spam logs too much on repeated errors.
1953  	 */
1954  	ratelimit_state_init(&btp->bt_ioerror_rl, 30 * HZ,
1955  			     DEFAULT_RATELIMIT_BURST);
1956  
1957  	if (xfs_setsize_buftarg_early(btp, bdev))
1958  		goto error_free;
1959  
1960  	if (list_lru_init(&btp->bt_lru))
1961  		goto error_free;
1962  
1963  	if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
1964  		goto error_lru;
1965  
1966  	btp->bt_shrinker.count_objects = xfs_buftarg_shrink_count;
1967  	btp->bt_shrinker.scan_objects = xfs_buftarg_shrink_scan;
1968  	btp->bt_shrinker.seeks = DEFAULT_SEEKS;
1969  	btp->bt_shrinker.flags = SHRINKER_NUMA_AWARE;
1970  	if (register_shrinker(&btp->bt_shrinker))
1971  		goto error_pcpu;
1972  	return btp;
1973  
1974  error_pcpu:
1975  	percpu_counter_destroy(&btp->bt_io_count);
1976  error_lru:
1977  	list_lru_destroy(&btp->bt_lru);
1978  error_free:
1979  	kmem_free(btp);
1980  	return NULL;
1981  }
1982  
1983  /*
1984   * Cancel a delayed write list.
1985   *
1986   * Remove each buffer from the list, clear the delwri queue flag and drop the
1987   * associated buffer reference.
1988   */
1989  void
1990  xfs_buf_delwri_cancel(
1991  	struct list_head	*list)
1992  {
1993  	struct xfs_buf		*bp;
1994  
1995  	while (!list_empty(list)) {
1996  		bp = list_first_entry(list, struct xfs_buf, b_list);
1997  
1998  		xfs_buf_lock(bp);
1999  		bp->b_flags &= ~_XBF_DELWRI_Q;
2000  		list_del_init(&bp->b_list);
2001  		xfs_buf_relse(bp);
2002  	}
2003  }
2004  
2005  /*
2006   * Add a buffer to the delayed write list.
2007   *
2008   * This queues a buffer for writeout if it hasn't already been.  Note that
2009   * neither this routine nor the buffer list submission functions perform
2010   * any internal synchronization.  It is expected that the lists are thread-local
2011   * to the callers.
2012   *
2013   * Returns true if we queued up the buffer, or false if it already had
2014   * been on the buffer list.
2015   */
2016  bool
2017  xfs_buf_delwri_queue(
2018  	struct xfs_buf		*bp,
2019  	struct list_head	*list)
2020  {
2021  	ASSERT(xfs_buf_islocked(bp));
2022  	ASSERT(!(bp->b_flags & XBF_READ));
2023  
2024  	/*
2025  	 * If the buffer is already marked delwri it already is queued up
2026  	 * by someone else for imediate writeout.  Just ignore it in that
2027  	 * case.
2028  	 */
2029  	if (bp->b_flags & _XBF_DELWRI_Q) {
2030  		trace_xfs_buf_delwri_queued(bp, _RET_IP_);
2031  		return false;
2032  	}
2033  
2034  	trace_xfs_buf_delwri_queue(bp, _RET_IP_);
2035  
2036  	/*
2037  	 * If a buffer gets written out synchronously or marked stale while it
2038  	 * is on a delwri list we lazily remove it. To do this, the other party
2039  	 * clears the  _XBF_DELWRI_Q flag but otherwise leaves the buffer alone.
2040  	 * It remains referenced and on the list.  In a rare corner case it
2041  	 * might get readded to a delwri list after the synchronous writeout, in
2042  	 * which case we need just need to re-add the flag here.
2043  	 */
2044  	bp->b_flags |= _XBF_DELWRI_Q;
2045  	if (list_empty(&bp->b_list)) {
2046  		atomic_inc(&bp->b_hold);
2047  		list_add_tail(&bp->b_list, list);
2048  	}
2049  
2050  	return true;
2051  }
2052  
2053  /*
2054   * Compare function is more complex than it needs to be because
2055   * the return value is only 32 bits and we are doing comparisons
2056   * on 64 bit values
2057   */
2058  static int
2059  xfs_buf_cmp(
2060  	void			*priv,
2061  	const struct list_head	*a,
2062  	const struct list_head	*b)
2063  {
2064  	struct xfs_buf	*ap = container_of(a, struct xfs_buf, b_list);
2065  	struct xfs_buf	*bp = container_of(b, struct xfs_buf, b_list);
2066  	xfs_daddr_t		diff;
2067  
2068  	diff = ap->b_maps[0].bm_bn - bp->b_maps[0].bm_bn;
2069  	if (diff < 0)
2070  		return -1;
2071  	if (diff > 0)
2072  		return 1;
2073  	return 0;
2074  }
2075  
2076  /*
2077   * Submit buffers for write. If wait_list is specified, the buffers are
2078   * submitted using sync I/O and placed on the wait list such that the caller can
2079   * iowait each buffer. Otherwise async I/O is used and the buffers are released
2080   * at I/O completion time. In either case, buffers remain locked until I/O
2081   * completes and the buffer is released from the queue.
2082   */
2083  static int
2084  xfs_buf_delwri_submit_buffers(
2085  	struct list_head	*buffer_list,
2086  	struct list_head	*wait_list)
2087  {
2088  	struct xfs_buf		*bp, *n;
2089  	int			pinned = 0;
2090  	struct blk_plug		plug;
2091  
2092  	list_sort(NULL, buffer_list, xfs_buf_cmp);
2093  
2094  	blk_start_plug(&plug);
2095  	list_for_each_entry_safe(bp, n, buffer_list, b_list) {
2096  		if (!wait_list) {
2097  			if (xfs_buf_ispinned(bp)) {
2098  				pinned++;
2099  				continue;
2100  			}
2101  			if (!xfs_buf_trylock(bp))
2102  				continue;
2103  		} else {
2104  			xfs_buf_lock(bp);
2105  		}
2106  
2107  		/*
2108  		 * Someone else might have written the buffer synchronously or
2109  		 * marked it stale in the meantime.  In that case only the
2110  		 * _XBF_DELWRI_Q flag got cleared, and we have to drop the
2111  		 * reference and remove it from the list here.
2112  		 */
2113  		if (!(bp->b_flags & _XBF_DELWRI_Q)) {
2114  			list_del_init(&bp->b_list);
2115  			xfs_buf_relse(bp);
2116  			continue;
2117  		}
2118  
2119  		trace_xfs_buf_delwri_split(bp, _RET_IP_);
2120  
2121  		/*
2122  		 * If we have a wait list, each buffer (and associated delwri
2123  		 * queue reference) transfers to it and is submitted
2124  		 * synchronously. Otherwise, drop the buffer from the delwri
2125  		 * queue and submit async.
2126  		 */
2127  		bp->b_flags &= ~_XBF_DELWRI_Q;
2128  		bp->b_flags |= XBF_WRITE;
2129  		if (wait_list) {
2130  			bp->b_flags &= ~XBF_ASYNC;
2131  			list_move_tail(&bp->b_list, wait_list);
2132  		} else {
2133  			bp->b_flags |= XBF_ASYNC;
2134  			list_del_init(&bp->b_list);
2135  		}
2136  		__xfs_buf_submit(bp, false);
2137  	}
2138  	blk_finish_plug(&plug);
2139  
2140  	return pinned;
2141  }
2142  
2143  /*
2144   * Write out a buffer list asynchronously.
2145   *
2146   * This will take the @buffer_list, write all non-locked and non-pinned buffers
2147   * out and not wait for I/O completion on any of the buffers.  This interface
2148   * is only safely useable for callers that can track I/O completion by higher
2149   * level means, e.g. AIL pushing as the @buffer_list is consumed in this
2150   * function.
2151   *
2152   * Note: this function will skip buffers it would block on, and in doing so
2153   * leaves them on @buffer_list so they can be retried on a later pass. As such,
2154   * it is up to the caller to ensure that the buffer list is fully submitted or
2155   * cancelled appropriately when they are finished with the list. Failure to
2156   * cancel or resubmit the list until it is empty will result in leaked buffers
2157   * at unmount time.
2158   */
2159  int
2160  xfs_buf_delwri_submit_nowait(
2161  	struct list_head	*buffer_list)
2162  {
2163  	return xfs_buf_delwri_submit_buffers(buffer_list, NULL);
2164  }
2165  
2166  /*
2167   * Write out a buffer list synchronously.
2168   *
2169   * This will take the @buffer_list, write all buffers out and wait for I/O
2170   * completion on all of the buffers. @buffer_list is consumed by the function,
2171   * so callers must have some other way of tracking buffers if they require such
2172   * functionality.
2173   */
2174  int
2175  xfs_buf_delwri_submit(
2176  	struct list_head	*buffer_list)
2177  {
2178  	LIST_HEAD		(wait_list);
2179  	int			error = 0, error2;
2180  	struct xfs_buf		*bp;
2181  
2182  	xfs_buf_delwri_submit_buffers(buffer_list, &wait_list);
2183  
2184  	/* Wait for IO to complete. */
2185  	while (!list_empty(&wait_list)) {
2186  		bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
2187  
2188  		list_del_init(&bp->b_list);
2189  
2190  		/*
2191  		 * Wait on the locked buffer, check for errors and unlock and
2192  		 * release the delwri queue reference.
2193  		 */
2194  		error2 = xfs_buf_iowait(bp);
2195  		xfs_buf_relse(bp);
2196  		if (!error)
2197  			error = error2;
2198  	}
2199  
2200  	return error;
2201  }
2202  
2203  /*
2204   * Push a single buffer on a delwri queue.
2205   *
2206   * The purpose of this function is to submit a single buffer of a delwri queue
2207   * and return with the buffer still on the original queue. The waiting delwri
2208   * buffer submission infrastructure guarantees transfer of the delwri queue
2209   * buffer reference to a temporary wait list. We reuse this infrastructure to
2210   * transfer the buffer back to the original queue.
2211   *
2212   * Note the buffer transitions from the queued state, to the submitted and wait
2213   * listed state and back to the queued state during this call. The buffer
2214   * locking and queue management logic between _delwri_pushbuf() and
2215   * _delwri_queue() guarantee that the buffer cannot be queued to another list
2216   * before returning.
2217   */
2218  int
2219  xfs_buf_delwri_pushbuf(
2220  	struct xfs_buf		*bp,
2221  	struct list_head	*buffer_list)
2222  {
2223  	LIST_HEAD		(submit_list);
2224  	int			error;
2225  
2226  	ASSERT(bp->b_flags & _XBF_DELWRI_Q);
2227  
2228  	trace_xfs_buf_delwri_pushbuf(bp, _RET_IP_);
2229  
2230  	/*
2231  	 * Isolate the buffer to a new local list so we can submit it for I/O
2232  	 * independently from the rest of the original list.
2233  	 */
2234  	xfs_buf_lock(bp);
2235  	list_move(&bp->b_list, &submit_list);
2236  	xfs_buf_unlock(bp);
2237  
2238  	/*
2239  	 * Delwri submission clears the DELWRI_Q buffer flag and returns with
2240  	 * the buffer on the wait list with the original reference. Rather than
2241  	 * bounce the buffer from a local wait list back to the original list
2242  	 * after I/O completion, reuse the original list as the wait list.
2243  	 */
2244  	xfs_buf_delwri_submit_buffers(&submit_list, buffer_list);
2245  
2246  	/*
2247  	 * The buffer is now locked, under I/O and wait listed on the original
2248  	 * delwri queue. Wait for I/O completion, restore the DELWRI_Q flag and
2249  	 * return with the buffer unlocked and on the original queue.
2250  	 */
2251  	error = xfs_buf_iowait(bp);
2252  	bp->b_flags |= _XBF_DELWRI_Q;
2253  	xfs_buf_unlock(bp);
2254  
2255  	return error;
2256  }
2257  
2258  int __init
2259  xfs_buf_init(void)
2260  {
2261  	xfs_buf_zone = kmem_cache_create("xfs_buf", sizeof(struct xfs_buf), 0,
2262  					 SLAB_HWCACHE_ALIGN |
2263  					 SLAB_RECLAIM_ACCOUNT |
2264  					 SLAB_MEM_SPREAD,
2265  					 NULL);
2266  	if (!xfs_buf_zone)
2267  		goto out;
2268  
2269  	return 0;
2270  
2271   out:
2272  	return -ENOMEM;
2273  }
2274  
2275  void
2276  xfs_buf_terminate(void)
2277  {
2278  	kmem_cache_destroy(xfs_buf_zone);
2279  }
2280  
2281  void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
2282  {
2283  	/*
2284  	 * Set the lru reference count to 0 based on the error injection tag.
2285  	 * This allows userspace to disrupt buffer caching for debug/testing
2286  	 * purposes.
2287  	 */
2288  	if (XFS_TEST_ERROR(false, bp->b_mount, XFS_ERRTAG_BUF_LRU_REF))
2289  		lru_ref = 0;
2290  
2291  	atomic_set(&bp->b_lru_ref, lru_ref);
2292  }
2293  
2294  /*
2295   * Verify an on-disk magic value against the magic value specified in the
2296   * verifier structure. The verifier magic is in disk byte order so the caller is
2297   * expected to pass the value directly from disk.
2298   */
2299  bool
2300  xfs_verify_magic(
2301  	struct xfs_buf		*bp,
2302  	__be32			dmagic)
2303  {
2304  	struct xfs_mount	*mp = bp->b_mount;
2305  	int			idx;
2306  
2307  	idx = xfs_has_crc(mp);
2308  	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic[idx]))
2309  		return false;
2310  	return dmagic == bp->b_ops->magic[idx];
2311  }
2312  /*
2313   * Verify an on-disk magic value against the magic value specified in the
2314   * verifier structure. The verifier magic is in disk byte order so the caller is
2315   * expected to pass the value directly from disk.
2316   */
2317  bool
2318  xfs_verify_magic16(
2319  	struct xfs_buf		*bp,
2320  	__be16			dmagic)
2321  {
2322  	struct xfs_mount	*mp = bp->b_mount;
2323  	int			idx;
2324  
2325  	idx = xfs_has_crc(mp);
2326  	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic16[idx]))
2327  		return false;
2328  	return dmagic == bp->b_ops->magic16[idx];
2329  }
2330