selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 2108 insertions, 0 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
new file mode 100644
index 000000000..ee7c2e9c0
--- /dev/null
+++ b/fs/xfs/xfs_buf.c
@@ -0,0 +1,2108 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2000-2006 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ */
+#include "xfs_platform.h"
+#include <linux/backing-dev.h>
+#include <linux/dax.h>
+
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_trace.h"
+#include "xfs_log.h"
+#include "xfs_log_recover.h"
+#include "xfs_log_priv.h"
+#include "xfs_trans.h"
+#include "xfs_buf_item.h"
+#include "xfs_errortag.h"
+#include "xfs_error.h"
+#include "xfs_ag.h"
+#include "xfs_buf_mem.h"
+#include "xfs_notify_failure.h"
+
+struct kmem_cache *xfs_buf_cache;
+
+/*
+ * Locking orders
+ *
+ * xfs_buf_stale:
+ *	b_sema (caller holds)
+ *	  b_lockref.lock
+ *	    lru_lock
+ *
+ * xfs_buf_rele:
+ *	b_lockref.lock
+ *	  lru_lock
+ *
+ * xfs_buftarg_drain_rele
+ *	lru_lock
+ *	  b_lockref.lock (trylock due to inversion)
+ *
+ * xfs_buftarg_isolate
+ *	lru_lock
+ *	  b_lockref.lock (trylock due to inversion)
+ */
+
+static void xfs_buf_submit(struct xfs_buf *bp);
+static int xfs_buf_iowait(struct xfs_buf *bp);
+
+static inline bool xfs_buf_is_uncached(struct xfs_buf *bp)
+{
+	return bp->b_rhash_key == XFS_BUF_DADDR_NULL;
+}
+
+static inline void
+xfs_buf_set_flags(
+	struct xfs_buf	*bp,
+	unsigned int	flags)
+{
+	WRITE_ONCE(bp->b_flags, bp->b_flags | flags);
+}
+
+static inline void
+xfs_buf_clear_flags(
+	struct xfs_buf	*bp,
+	unsigned int	flags)
+{
+	WRITE_ONCE(bp->b_flags, bp->b_flags & ~flags);
+}
+
+void
+xfs_buf_set_uptodate(
+	struct xfs_buf	*bp)
+{
+	xfs_buf_set_flags(bp, XBF_DONE);
+}
+
+/*
+ * When we mark a buffer stale, we remove the buffer from the LRU and clear the
+ * b_lru_ref count so that the buffer is freed immediately when the buffer
+ * reference count falls to zero. If the buffer is already on the LRU, we need
+ * to remove the reference that LRU holds on the buffer.
+ *
+ * This prevents build-up of stale buffers on the LRU.
+ */
+void
+xfs_buf_stale(
+	struct xfs_buf	*bp)
+{
+	ASSERT(xfs_buf_islocked(bp));
+
+	xfs_buf_set_flags(bp, XBF_STALE);
+
+	/*
+	 * Clear the delwri status so that a delwri queue walker will not
+	 * flush this buffer to disk now that it is stale. The delwri queue has
+	 * a reference to the buffer, so this is safe to do.
+	 */
+	xfs_buf_clear_flags(bp, _XBF_DELWRI_Q);
+
+	spin_lock(&bp->b_lockref.lock);
+	atomic_set(&bp->b_lru_ref, 0);
+	if (!lockref_is_dead(&bp->b_lockref))
+		list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru);
+	spin_unlock(&bp->b_lockref.lock);
+}
+
+void
+xfs_buf_clear_stale(
+	struct xfs_buf	*bp)
+{
+	ASSERT(bp->b_flags & XBF_STALE);
+	xfs_buf_clear_flags(bp, XBF_STALE);
+}
+
+static void
+xfs_buf_free_callback(
+	struct callback_head	*cb)
+{
+	struct xfs_buf		*bp = container_of(cb, struct xfs_buf, b_rcu);
+
+	if (bp->b_maps != &bp->__b_map)
+		kfree(bp->b_maps);
+	kmem_cache_free(xfs_buf_cache, bp);
+}
+
+static void
+xfs_buf_free(
+	struct xfs_buf		*bp)
+{
+	unsigned int		size = BBTOB(bp->b_length);
+
+	might_sleep();
+	trace_xfs_buf_free(bp, _RET_IP_);
+
+	ASSERT(list_empty(&bp->b_lru));
+
+	if (!xfs_buftarg_is_mem(bp->b_target) && size >= PAGE_SIZE)
+		mm_account_reclaimed_pages(howmany(size, PAGE_SHIFT));
+
+	if (is_vmalloc_addr(bp->b_addr))
+		vfree(bp->b_addr);
+	else if (bp->b_flags & _XBF_KMEM)
+		kfree(bp->b_addr);
+	else if (bp->b_addr)
+		folio_put(virt_to_folio(bp->b_addr));
+
+	call_rcu(&bp->b_rcu, xfs_buf_free_callback);
+}
+
+static int
+xfs_buf_alloc_folio(
+	struct xfs_buf		*bp,
+	size_t			size,
+	gfp_t			gfp_mask)
+{
+	struct folio		*folio;
+
+	folio = folio_alloc(gfp_mask, get_order(size));
+	if (!folio)
+		return -ENOMEM;
+	bp->b_addr = folio_address(folio);
+	trace_xfs_buf_backing_folio(bp, _RET_IP_);
+	return 0;
+}
+
+static int
+xfs_buf_alloc_kmem(
+	struct xfs_buf		*bp,
+	size_t			size,
+	gfp_t			gfp_mask)
+{
+	ASSERT(is_power_of_2(size));
+	ASSERT(size < PAGE_SIZE);
+
+	bp->b_addr = kmalloc(size, gfp_mask);
+	if (!bp->b_addr)
+		return -ENOMEM;
+
+	/*
+	 * Slab guarantees that we get back naturally aligned allocations for
+	 * power of two sizes.  Keep this check as the canary in the coal mine
+	 * if anything changes in slab.
+	 */
+	if (WARN_ON_ONCE(!IS_ALIGNED((unsigned long)bp->b_addr, size))) {
+		kfree(bp->b_addr);
+		bp->b_addr = NULL;
+		return -ENOMEM;
+	}
+	xfs_buf_set_flags(bp, _XBF_KMEM);
+	trace_xfs_buf_backing_kmem(bp, _RET_IP_);
+	return 0;
+}
+
+static int
+xfs_buf_alloc_vmalloc(
+	struct xfs_buf		*bp,
+	size_t			size,
+	gfp_t			gfp_mask)
+{
+	for (;;) {
+		bp->b_addr = __vmalloc(size, gfp_mask);
+		if (bp->b_addr)
+			break;
+		if (gfp_mask & __GFP_NORETRY)
+			return -ENOMEM;
+		XFS_STATS_INC(bp->b_mount, xb_page_retries);
+		memalloc_retry_wait(gfp_mask);
+	}
+
+	trace_xfs_buf_backing_vmalloc(bp, _RET_IP_);
+	return 0;
+}
+
+/*
+ * Allocate backing memory for a buffer.
+ *
+ * For tmpfs-backed buffers used by in-memory btrees this directly maps the
+ * tmpfs page cache folios.
+ *
+ * For real file system buffers there are three different kinds backing memory:
+ *
+ * The first type backs the buffer by a kmalloc allocation.  This is done for
+ * less than PAGE_SIZE allocations to avoid wasting memory.
+ *
+ * The second type is a single folio buffer - this may be a high order folio or
+ * just a single page sized folio, but either way they get treated the same way
+ * by the rest of the code - the buffer memory spans a single contiguous memory
+ * region that we don't have to map and unmap to access the data directly.
+ *
+ * The third type of buffer is the vmalloc()d buffer. This provides the buffer
+ * with the required contiguous memory region but backed by discontiguous
+ * physical pages.
+ */
+static int
+xfs_buf_alloc_backing_mem(
+	struct xfs_buf	*bp,
+	xfs_buf_flags_t	flags)
+{
+	size_t		size = BBTOB(bp->b_length);
+	gfp_t		gfp_mask = GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOWARN;
+
+	if (xfs_buftarg_is_mem(bp->b_target))
+		return xmbuf_map_backing_mem(bp);
+
+	/* Assure zeroed buffer for non-read cases. */
+	if (!(flags & XBF_READ))
+		gfp_mask |= __GFP_ZERO;
+
+	if (flags & XBF_READ_AHEAD)
+		gfp_mask |= __GFP_NORETRY;
+
+	/*
+	 * Optimistically attempt a single high order folio allocation for
+	 * larger than PAGE_SIZE buffers.
+	 *
+	 * Allocating a high order folio makes the assumption that buffers are a
+	 * power-of-2 size, matching the power-of-2 folios sizes available.
+	 *
+	 * The exception here are user xattr data buffers, which can be arbitrarily
+	 * sized up to 64kB plus structure metadata, skip straight to the vmalloc
+	 * path for them instead of wasting memory here.
+	 */
+	if (size > PAGE_SIZE) {
+		if (is_power_of_2(size)) {
+			gfp_t folio_gfp = gfp_mask;
+
+			folio_gfp &= ~__GFP_DIRECT_RECLAIM;
+			folio_gfp |= __GFP_NORETRY;
+			if (xfs_buf_alloc_folio(bp, size, folio_gfp) == 0)
+				return 0;
+			trace_xfs_buf_backing_fallback(bp, _RET_IP_);
+		}
+		return xfs_buf_alloc_vmalloc(bp, size, gfp_mask);
+	}
+
+	/*
+	 * The slab allocator now guarantees aligned allocations for all power
+	 * of two sizes.  This covers most smaller XFS buffers, so just use
+	 * kmalloc in this case.
+	 *
+	 * Don't bother with the vmalloc fallback for allocations of page size
+	 * or less: vmalloc won't do any better.
+	 */
+	if (!(gfp_mask & __GFP_NORETRY))
+		gfp_mask |= __GFP_NOFAIL;
+	if (size < PAGE_SIZE && is_power_of_2(size))
+		return xfs_buf_alloc_kmem(bp, size, gfp_mask);
+	return xfs_buf_alloc_folio(bp, size, gfp_mask);
+}
+
+static int
+xfs_buf_alloc(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf		*bp;
+	int			error;
+	int			i;
+
+	*bpp = NULL;
+	bp = kmem_cache_zalloc(xfs_buf_cache,
+			GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);
+
+	/*
+	 * We don't want certain flags to appear in b_flags unless they are
+	 * specifically set by later operations on the buffer.
+	 */
+	flags &= ~(XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD);
+	lockref_init(&bp->b_lockref);
+	sema_init(&bp->b_sema, 1); /* unlocked */
+	atomic_set(&bp->b_lru_ref, 1);
+	init_completion(&bp->b_iowait);
+	INIT_LIST_HEAD(&bp->b_lru);
+	INIT_LIST_HEAD(&bp->b_list);
+	INIT_LIST_HEAD(&bp->b_li_list);
+	bp->b_target = target;
+	bp->b_mount = target->bt_mount;
+	WRITE_ONCE(bp->b_flags, flags);
+	bp->b_rhash_key = map[0].bm_bn;
+	bp->b_length = 0;
+	bp->b_map_count = nmaps;
+	if (nmaps == 1)
+		bp->b_maps = &bp->__b_map;
+	else
+		bp->b_maps = kzalloc_objs(struct xfs_buf_map, nmaps,
+					  GFP_KERNEL | __GFP_NOLOCKDEP | __GFP_NOFAIL);
+	for (i = 0; i < nmaps; i++) {
+		bp->b_maps[i].bm_bn = map[i].bm_bn;
+		bp->b_maps[i].bm_len = map[i].bm_len;
+		bp->b_length += map[i].bm_len;
+	}
+
+	atomic_set(&bp->b_pin_count, 0);
+	init_waitqueue_head(&bp->b_waiters);
+
+	XFS_STATS_INC(bp->b_mount, xb_create);
+	trace_xfs_buf_init(bp, _RET_IP_);
+
+	error = xfs_buf_alloc_backing_mem(bp, flags);
+	if (error) {
+		xfs_buf_free(bp);
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+/*
+ *	Finding and Reading Buffers
+ */
+static int
+_xfs_buf_obj_cmp(
+	struct rhashtable_compare_arg	*arg,
+	const void			*obj)
+{
+	const struct xfs_buf_map	*map = arg->key;
+	const struct xfs_buf		*bp = obj;
+
+	/*
+	 * The key hashing in the lookup path depends on the key being the
+	 * first element of the compare_arg, make sure to assert this.
+	 */
+	BUILD_BUG_ON(offsetof(struct xfs_buf_map, bm_bn) != 0);
+
+	if (bp->b_rhash_key != map->bm_bn)
+		return 1;
+
+	if (unlikely(bp->b_length != map->bm_len)) {
+		/*
+		 * found a block number match. If the range doesn't
+		 * match, the only way this is allowed is if the buffer
+		 * in the cache is stale and the transaction that made
+		 * it stale has not yet committed. i.e. we are
+		 * reallocating a busy extent. Skip this buffer and
+		 * continue searching for an exact match.
+		 *
+		 * Note: If we're scanning for incore buffers to stale, don't
+		 * complain if we find non-stale buffers.
+		 */
+		if (!(map->bm_flags & XBM_LIVESCAN))
+			ASSERT(bp->b_flags & XBF_STALE);
+		return 1;
+	}
+	return 0;
+}
+
+static const struct rhashtable_params xfs_buf_hash_params = {
+	.min_size		= 32,	/* empty AGs have minimal footprint */
+	.nelem_hint		= 16,
+	.key_len		= sizeof(xfs_daddr_t),
+	.key_offset		= offsetof(struct xfs_buf, b_rhash_key),
+	.head_offset		= offsetof(struct xfs_buf, b_rhash_head),
+	.automatic_shrinking	= true,
+	.obj_cmpfn		= _xfs_buf_obj_cmp,
+};
+
+static int
+xfs_buf_map_verify(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map)
+{
+	/* Check for IOs smaller than the sector size / not sector aligned */
+	ASSERT(!(BBTOB(map->bm_len) < btp->bt_meta_sectorsize));
+	ASSERT(!(BBTOB(map->bm_bn) & (xfs_off_t)btp->bt_meta_sectormask));
+
+	/*
+	 * Corrupted block numbers can get through to here, unfortunately, so we
+	 * have to check that the buffer falls within the filesystem bounds.
+	 */
+	if (map->bm_bn < 0 || map->bm_bn >= btp->bt_nr_sectors) {
+		xfs_alert(btp->bt_mount,
+			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",
+			  __func__, map->bm_bn, btp->bt_nr_sectors);
+		WARN_ON(1);
+		return -EFSCORRUPTED;
+	}
+	return 0;
+}
+
+static int
+xfs_buf_find_lock(
+	struct xfs_buf          *bp,
+	xfs_buf_flags_t		flags)
+{
+	if (flags & XBF_TRYLOCK) {
+		if (!xfs_buf_trylock(bp)) {
+			XFS_STATS_INC(bp->b_mount, xb_busy_locked);
+			return -EAGAIN;
+		}
+	} else {
+		xfs_buf_lock(bp);
+		XFS_STATS_INC(bp->b_mount, xb_get_locked_waited);
+	}
+
+	/*
+	 * if the buffer is stale, clear all the external state associated with
+	 * it. We need to keep flags such as how we allocated the buffer memory
+	 * intact here.
+	 */
+	if (bp->b_flags & XBF_STALE) {
+		if (flags & XBF_LIVESCAN) {
+			xfs_buf_unlock(bp);
+			return -ENOENT;
+		}
+		ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0);
+		xfs_buf_clear_flags(bp, ~_XBF_KMEM);
+		bp->b_ops = NULL;
+	}
+	return 0;
+}
+
+static inline struct xfs_buf *
+xfs_buf_lookup(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map)
+{
+	struct xfs_buf          *bp;
+
+	rcu_read_lock();
+	bp = rhashtable_lookup(&btp->bt_hash, map, xfs_buf_hash_params);
+	if (!bp || !lockref_get_not_dead(&bp->b_lockref)) {
+		rcu_read_unlock();
+		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);
+		return NULL;
+	}
+	rcu_read_unlock();
+
+	trace_xfs_buf_find(bp, _RET_IP_);
+	XFS_STATS_INC(btp->bt_mount, xb_get_locked);
+	return bp;
+}
+
+/*
+ * Insert the new_bp into the hash table. This consumes the perag reference
+ * taken for the lookup regardless of the result of the insert.
+ */
+static int
+xfs_buf_find_insert(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*cmap,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf		*new_bp;
+	struct xfs_buf		*bp;
+	int			error;
+
+	error = xfs_buf_alloc(btp, map, nmaps, flags, &new_bp);
+	if (error)
+		return error;
+
+	/* The new buffer keeps the perag reference until it is freed. */
+	if (!xfs_buftarg_is_mem(btp)) {
+		new_bp->b_pag = xfs_perag_get(btp->bt_mount,
+			xfs_daddr_to_agno(btp->bt_mount, cmap->bm_bn));
+	}
+
+retry:
+	rcu_read_lock();
+	bp = rhashtable_lookup_get_insert_fast(&btp->bt_hash,
+			&new_bp->b_rhash_head, xfs_buf_hash_params);
+	if (IS_ERR(bp)) {
+		rcu_read_unlock();
+		error = PTR_ERR(bp);
+		goto out_free_buf;
+	}
+	if (bp) {
+		/*
+		 * If there is an existing buffer with a dead lockref, retry
+		 * until the new buffer is added, or a usable buffer is found.
+		 */
+		if (!lockref_get_not_dead(&bp->b_lockref)) {
+			rcu_read_unlock();
+			cpu_relax();
+			goto retry;
+		}
+		rcu_read_unlock();
+		*bpp = bp;
+		goto out_free_buf;
+	}
+	rcu_read_unlock();
+
+	*bpp = new_bp;
+	return 0;
+
+out_free_buf:
+	if (new_bp->b_pag)
+		xfs_perag_put(new_bp->b_pag);
+	xfs_buf_free(new_bp);
+	return error;
+}
+
+/*
+ * Assembles a buffer covering the specified range. The code is optimised for
+ * cache hits, as metadata intensive workloads will see 3 orders of magnitude
+ * more hits than misses.
+ */
+static int
+xfs_find_get_buf(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	struct xfs_buf		*bp = NULL;
+	struct xfs_buf_map	cmap = { .bm_bn = map[0].bm_bn };
+	int			error;
+	int			i;
+
+	if (flags & XBF_LIVESCAN)
+		cmap.bm_flags |= XBM_LIVESCAN;
+	for (i = 0; i < nmaps; i++)
+		cmap.bm_len += map[i].bm_len;
+
+	error = xfs_buf_map_verify(btp, &cmap);
+	if (error)
+		return error;
+
+	/* cache hits always outnumber misses by at least 10:1 */
+	bp = xfs_buf_lookup(btp, &cmap);
+	if (unlikely(!bp)) {
+		if (flags & XBF_INCORE)
+			return -ENOENT;
+		error = xfs_buf_find_insert(btp, &cmap, map, nmaps, flags, &bp);
+		if (error)
+			return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+int
+xfs_buf_get_map(
+	struct xfs_buftarg	*btp,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
+{
+	int			error;
+
+	ASSERT(!(flags & ~(XBF_TRYLOCK | XBF_INCORE | XBF_LIVESCAN)));
+	ASSERT(!(flags & XBF_LIVESCAN) || (flags & XBF_INCORE));
+
+	/*
+	 * Zero the buffer and clear b_error as xfs_buf_get_map callers don't
+	 * expect valid data to be found in the buffer.
+	 */
+	error = xfs_find_get_buf(btp, map, nmaps, flags, bpp);
+	if (error)
+		return error;
+
+	error = xfs_buf_find_lock(*bpp, flags);
+	if (error) {
+		xfs_buf_rele(*bpp);
+		return error;
+	}
+	XFS_STATS_INC(btp->bt_mount, xb_get);
+	trace_xfs_buf_get(*bpp, flags, _RET_IP_);
+	xfs_buf_ioerror(*bpp, 0);
+	return 0;
+}
+
+int
+_xfs_buf_read(
+	struct xfs_buf		*bp)
+{
+	ASSERT(bp->b_maps[0].bm_bn != XFS_BUF_DADDR_NULL);
+
+	xfs_buf_clear_flags(bp, XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD |
+			XBF_DONE);
+	xfs_buf_set_flags(bp, XBF_READ);
+	xfs_buf_submit(bp);
+	return xfs_buf_iowait(bp);
+}
+
+int
+xfs_buf_read_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp,
+	const struct xfs_buf_ops *ops,
+	xfs_failaddr_t		fa)
+{
+	struct xfs_buf		*bp;
+	int			error;
+
+	ASSERT(!(flags & ~XBF_TRYLOCK));
+
+	flags |= XBF_READ;
+	*bpp = NULL;
+
+	error = xfs_find_get_buf(target, map, nmaps, flags, &bp);
+	if (error)
+		return error;
+	error = xfs_buf_find_lock(bp, flags);
+	if (error) {
+		xfs_buf_rele(bp);
+		return error;
+	}
+
+	trace_xfs_buf_read(bp, flags, _RET_IP_);
+
+	if (bp->b_flags & XBF_DONE) {
+		ASSERT(bp->b_error == 0);
+
+		/*
+		 * If the caller passed an ops structure and the buffer doesn't
+		 * have ops assigned yet, set the ops and use them to verify the
+		 * buffer contents.
+		 *
+		 * Under normal operations, every in-core buffer is verified on
+		 * read I/O completion, but there are two scenarios that can
+		 * lead to in-core buffers without an assigned ->b_ops:
+		 *
+		 *   1) During log recovery of buffers on a V4 filesystem.
+		 *	These buffers are purged at the end of recovery, though.
+		 *   2) Oonline repair intentionally reads with a NULL buffer
+		 *	ops to run several verifiers across an in-core buffer in
+		 *	order to establish buffer type.  If repair can't
+		 *	establish that, the buffer will be left in memory with
+		 *	NULL buffer ops.
+		 */
+		if (ops && !bp->b_ops) {
+			bp->b_ops = ops;
+			bp->b_ops->verify_read(bp);
+			/*
+			 * If verification failed, clear XBF_DONE as we assume
+			 * that buffers have no recorded errors when in XBF_DONE
+			 * state.
+			 */
+			error = bp->b_error;
+			if (error)
+				xfs_buf_clear_flags(bp, XBF_DONE);
+		}
+
+		/* We do not want read in the flags */
+		xfs_buf_clear_flags(bp, XBF_READ);
+	} else {
+		/* Initiate the buffer read and wait. */
+		XFS_STATS_INC(target->bt_mount, xb_get_read);
+		bp->b_ops = ops;
+		error = _xfs_buf_read(bp);
+	}
+
+	if (error)
+		goto out_ioerror;
+
+	*bpp = bp;
+	return 0;
+
+out_ioerror:
+	/*
+	 * Check against log shutdown for error reporting because metadata
+	 * writeback may require a read first and we need to report errors in
+	 * metadata writeback until the log is shut down.  High level
+	 * transaction read functions already check against mount shutdown, so
+	 * we only need to be concerned about low level/ IO interactions here.
+	 */
+	if (!xlog_is_shutdown(target->bt_mount->m_log))
+		xfs_buf_ioerror_alert(bp, fa);
+
+	/*
+	 * If we've had a read error, then the contents of the buffer are
+	 * invalid and should not be used. To ensure that a followup read tries
+	 * to pull the buffer from disk again, we clear the XBF_DONE flag and
+	 * mark the buffer stale. This ensures that anyone who has a current
+	 * reference to the buffer will interpret it's contents correctly and
+	 * future cache lookups will also treat it as an empty, uninitialised
+	 * buffer.
+	 */
+	xfs_buf_clear_flags(bp, XBF_DONE);
+	xfs_buf_stale(bp);
+	xfs_buf_relse(bp);
+
+	/* bad CRC means corrupted metadata */
+	if (error == -EFSBADCRC)
+		return -EFSCORRUPTED;
+	return error;
+}
+
+/*
+ *	If we are not low on memory then do the readahead in a deadlock
+ *	safe manner.
+ */
+void
+xfs_buf_readahead_map(
+	struct xfs_buftarg	*target,
+	struct xfs_buf_map	*map,
+	int			nmaps,
+	const struct xfs_buf_ops *ops)
+{
+	const xfs_buf_flags_t	flags = XBF_READ | XBF_ASYNC | XBF_READ_AHEAD;
+	struct xfs_buf		*bp;
+
+	/*
+	 * Currently we don't have a good means or justification for performing
+	 * xmbuf_map_page asynchronously, so we don't do readahead.
+	 */
+	if (xfs_buftarg_is_mem(target))
+		return;
+
+	if (xfs_find_get_buf(target, map, nmaps, flags, &bp))
+		return;
+
+	/*
+	 * Do a lockless fast path check for a valid uptodate buffer and avoid
+	 * locking entirely in this case.
+	 */
+	if ((READ_ONCE(bp->b_flags) & (XBF_DONE | XBF_STALE)) == XBF_DONE)
+		goto out_rele;
+
+	/* Otherwise lock the buffer to stabilize the state */
+	if (!xfs_buf_trylock(bp))
+		goto out_rele;
+
+	/* Let the actual reader deal with stale buffers. */
+	if (bp->b_flags & (XBF_STALE | XBF_DONE))
+		goto out_unlock;
+
+	trace_xfs_buf_readahead(bp, 0, _RET_IP_);
+	XFS_STATS_INC(target->bt_mount, xb_get_read);
+	bp->b_ops = ops;
+	xfs_buf_clear_flags(bp, XBF_WRITE | XBF_DONE);
+	xfs_buf_set_flags(bp, flags);
+	percpu_counter_inc(&target->bt_readahead_count);
+	xfs_buf_submit(bp);
+	return;
+out_unlock:
+	xfs_buf_unlock(bp);
+out_rele:
+	xfs_buf_rele(bp);
+}
+
+/*
+ * Read an uncached buffer from disk. Allocates and returns a locked
+ * buffer containing the disk contents or nothing. Uncached buffers always have
+ * a cache index of XFS_BUF_DADDR_NULL so we can easily determine if the buffer
+ * is cached or uncached during fault diagnosis.
+ */
+int
+xfs_buf_read_uncached(
+	struct xfs_buftarg	*target,
+	xfs_daddr_t		daddr,
+	size_t			numblks,
+	struct xfs_buf		**bpp,
+	const struct xfs_buf_ops *ops)
+{
+	struct xfs_buf		*bp;
+	int			error;
+
+	*bpp = NULL;
+
+	error = xfs_buf_get_uncached(target, numblks, &bp);
+	if (error)
+		return error;
+
+	/* set up the buffer for a read IO */
+	ASSERT(bp->b_map_count == 1);
+	bp->b_rhash_key = XFS_BUF_DADDR_NULL;
+	bp->b_maps[0].bm_bn = daddr;
+	xfs_buf_set_flags(bp, XBF_READ);
+	bp->b_ops = ops;
+
+	xfs_buf_submit(bp);
+	error = xfs_buf_iowait(bp);
+	if (error) {
+		xfs_buf_relse(bp);
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
+}
+
+int
+xfs_buf_get_uncached(
+	struct xfs_buftarg	*target,
+	size_t			numblks,
+	struct xfs_buf		**bpp)
+{
+	int			error;
+	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
+
+	error = xfs_buf_alloc(target, &map, 1, 0, bpp);
+	if (error)
+		return error;
+	xfs_buf_lock(*bpp);
+	trace_xfs_buf_get_uncached(*bpp, _RET_IP_);
+	return 0;
+}
+
+/*
+ *	Increment reference count on buffer, to hold the buffer concurrently
+ *	with another thread which may release (free) the buffer asynchronously.
+ *	Must hold the buffer already to call this function.
+ */
+void
+xfs_buf_hold(
+	struct xfs_buf		*bp)
+{
+	trace_xfs_buf_hold(bp, _RET_IP_);
+
+	lockref_get(&bp->b_lockref);
+}
+
+static void
+xfs_buf_destroy(
+	struct xfs_buf		*bp)
+{
+	ASSERT(lockref_is_dead(&bp->b_lockref));
+	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+
+	if (bp->b_pag)
+		xfs_perag_put(bp->b_pag);
+	xfs_buf_free(bp);
+}
+
+static inline void
+xfs_buf_kill(
+	struct xfs_buf		*bp)
+{
+	lockref_mark_dead(&bp->b_lockref);
+	if (!xfs_buf_is_uncached(bp)) {
+		rhashtable_remove_fast(&bp->b_target->bt_hash,
+				&bp->b_rhash_head, xfs_buf_hash_params);
+	}
+}
+
+/*
+ * Release a hold on the specified buffer.
+ */
+void
+xfs_buf_rele(
+	struct xfs_buf		*bp)
+{
+	trace_xfs_buf_rele(bp, _RET_IP_);
+
+	if (lockref_put_or_lock(&bp->b_lockref))
+		return;
+	if (!--bp->b_lockref.count) {
+		if (xfs_buf_is_uncached(bp) || !atomic_read(&bp->b_lru_ref))
+			goto kill;
+		list_lru_add_obj(&bp->b_target->bt_lru, &bp->b_lru);
+	}
+	spin_unlock(&bp->b_lockref.lock);
+	return;
+
+kill:
+	xfs_buf_kill(bp);
+	list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru);
+	spin_unlock(&bp->b_lockref.lock);
+
+	xfs_buf_destroy(bp);
+}
+
+/*
+ *	Lock a buffer object, if it is not already locked.
+ *
+ *	If we come across a stale, pinned, locked buffer, we know that we are
+ *	being asked to lock a buffer that has been reallocated. Because it is
+ *	pinned, we know that the log has not been pushed to disk and hence it
+ *	will still be locked.  Rather than continuing to have trylock attempts
+ *	fail until someone else pushes the log, push it ourselves before
+ *	returning.  This means that the xfsaild will not get stuck trying
+ *	to push on stale inode buffers.
+ */
+int
+xfs_buf_trylock(
+	struct xfs_buf		*bp)
+{
+	int			locked;
+
+	locked = down_trylock(&bp->b_sema) == 0;
+	if (locked)
+		trace_xfs_buf_trylock(bp, _RET_IP_);
+	else
+		trace_xfs_buf_trylock_fail(bp, _RET_IP_);
+	return locked;
+}
+
+/*
+ *	Lock a buffer object.
+ *
+ *	If we come across a stale, pinned, locked buffer, we know that we
+ *	are being asked to lock a buffer that has been reallocated. Because
+ *	it is pinned, we know that the log has not been pushed to disk and
+ *	hence it will still be locked. Rather than sleeping until someone
+ *	else pushes the log, push it ourselves before trying to get the lock.
+ */
+void
+xfs_buf_lock(
+	struct xfs_buf		*bp)
+{
+	trace_xfs_buf_lock(bp, _RET_IP_);
+
+	if (atomic_read(&bp->b_pin_count) && (bp->b_flags & XBF_STALE))
+		xfs_log_force(bp->b_mount, 0);
+	down(&bp->b_sema);
+
+	trace_xfs_buf_lock_done(bp, _RET_IP_);
+}
+
+void
+xfs_buf_unlock(
+	struct xfs_buf		*bp)
+{
+	ASSERT(xfs_buf_islocked(bp));
+
+	up(&bp->b_sema);
+	trace_xfs_buf_unlock(bp, _RET_IP_);
+}
+
+STATIC void
+xfs_buf_wait_unpin(
+	struct xfs_buf		*bp)
+{
+	DECLARE_WAITQUEUE	(wait, current);
+
+	if (atomic_read(&bp->b_pin_count) == 0)
+		return;
+
+	add_wait_queue(&bp->b_waiters, &wait);
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (atomic_read(&bp->b_pin_count) == 0)
+			break;
+		io_schedule();
+	}
+	remove_wait_queue(&bp->b_waiters, &wait);
+	set_current_state(TASK_RUNNING);
+}
+
+static void
+xfs_buf_ioerror_alert_ratelimited(
+	struct xfs_buf		*bp)
+{
+	static unsigned long	lasttime;
+	static struct xfs_buftarg *lasttarg;
+
+	if (bp->b_target != lasttarg ||
+	    time_after(jiffies, (lasttime + 5*HZ))) {
+		lasttime = jiffies;
+		xfs_buf_ioerror_alert(bp, __this_address);
+	}
+	lasttarg = bp->b_target;
+}
+
+/*
+ * Account for this latest trip around the retry handler, and decide if
+ * we've failed enough times to constitute a permanent failure.
+ */
+static bool
+xfs_buf_ioerror_permanent(
+	struct xfs_buf		*bp,
+	struct xfs_error_cfg	*cfg)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+
+	if (cfg->max_retries != XFS_ERR_RETRY_FOREVER &&
+	    ++bp->b_retries > cfg->max_retries)
+		return true;
+	if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
+	    time_after(jiffies, cfg->retry_timeout + bp->b_first_retry_time))
+		return true;
+
+	/* At unmount we may treat errors differently */
+	if (xfs_is_unmounting(mp) && mp->m_fail_unmount)
+		return true;
+
+	return false;
+}
+
+/*
+ * On a sync write or shutdown we just want to stale the buffer and let the
+ * caller handle the error in bp->b_error appropriately.
+ *
+ * If the write was asynchronous then no one will be looking for the error.  If
+ * this is the first failure of this type, clear the error state and write the
+ * buffer out again. This means we always retry an async write failure at least
+ * once, but we also need to set the buffer up to behave correctly now for
+ * repeated failures.
+ *
+ * If we get repeated async write failures, then we take action according to the
+ * error configuration we have been set up to use.
+ *
+ * Returns true if this function took care of error handling and the caller must
+ * not touch the buffer again.  Return false if the caller should proceed with
+ * normal I/O completion handling.
+ */
+static bool
+xfs_buf_ioend_handle_error(
+	struct xfs_buf		*bp)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	struct xfs_error_cfg	*cfg;
+	struct xfs_log_item	*lip;
+
+	/*
+	 * If we've already shutdown the journal because of I/O errors, there's
+	 * no point in giving this a retry.
+	 */
+	if (xlog_is_shutdown(mp->m_log))
+		goto out_stale;
+
+	xfs_buf_ioerror_alert_ratelimited(bp);
+
+	/*
+	 * We're not going to bother about retrying this during recovery.
+	 * One strike!
+	 */
+	if (mp->m_log && xlog_in_recovery(mp->m_log)) {
+		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
+		return false;
+	}
+
+	/*
+	 * Synchronous writes will have callers process the error.
+	 */
+	if (!(bp->b_flags & XBF_ASYNC))
+		goto out_stale;
+
+	trace_xfs_buf_iodone_async(bp, _RET_IP_);
+
+	cfg = xfs_error_get_cfg(mp, XFS_ERR_METADATA, bp->b_error);
+	if (bp->b_last_error != bp->b_error ||
+	    !(bp->b_flags & (XBF_STALE | XBF_WRITE_FAIL))) {
+		bp->b_last_error = bp->b_error;
+		if (cfg->retry_timeout != XFS_ERR_RETRY_FOREVER &&
+		    !bp->b_first_retry_time)
+			bp->b_first_retry_time = jiffies;
+		goto resubmit;
+	}
+
+	/*
+	 * Permanent error - we need to trigger a shutdown if we haven't already
+	 * to indicate that inconsistency will result from this action.
+	 */
+	if (xfs_buf_ioerror_permanent(bp, cfg)) {
+		xfs_force_shutdown(mp, SHUTDOWN_META_IO_ERROR);
+		goto out_stale;
+	}
+
+	/* Still considered a transient error. Caller will schedule retries. */
+	list_for_each_entry(lip, &bp->b_li_list, li_bio_list) {
+		set_bit(XFS_LI_FAILED, &lip->li_flags);
+		clear_bit(XFS_LI_FLUSHING, &lip->li_flags);
+	}
+
+	xfs_buf_ioerror(bp, 0);
+	xfs_buf_relse(bp);
+	return true;
+
+resubmit:
+	xfs_buf_ioerror(bp, 0);
+	xfs_buf_set_flags(bp, XBF_DONE | XBF_WRITE_FAIL);
+	reinit_completion(&bp->b_iowait);
+	xfs_buf_submit(bp);
+	return true;
+out_stale:
+	xfs_buf_stale(bp);
+	xfs_buf_set_flags(bp, XBF_DONE);
+	xfs_buf_clear_flags(bp, XBF_WRITE);
+	trace_xfs_buf_error_relse(bp, _RET_IP_);
+	return false;
+}
+
+/*
+ * Complete a buffer read or write.
+ *
+ * Releases the buffer if the I/O was asynchronous.
+ */
+static void
+xfs_buf_ioend(
+	struct xfs_buf	*bp)
+{
+	bool		async = bp->b_flags & XBF_ASYNC;
+
+	trace_xfs_buf_iodone(bp, _RET_IP_);
+
+	if (bp->b_flags & XBF_READ) {
+		if (!bp->b_error && is_vmalloc_addr(bp->b_addr))
+			invalidate_kernel_vmap_range(bp->b_addr,
+				roundup(BBTOB(bp->b_length), PAGE_SIZE));
+		if (!bp->b_error && bp->b_ops)
+			bp->b_ops->verify_read(bp);
+		if (!bp->b_error)
+			xfs_buf_set_flags(bp, XBF_DONE);
+		if (bp->b_flags & XBF_READ_AHEAD)
+			percpu_counter_dec(&bp->b_target->bt_readahead_count);
+	} else {
+		if (unlikely(bp->b_error)) {
+			if (xfs_buf_ioend_handle_error(bp)) {
+				ASSERT(async);
+				return;
+			}
+		} else {
+			xfs_buf_clear_flags(bp, XBF_WRITE_FAIL);
+			xfs_buf_set_flags(bp, XBF_DONE);
+		}
+
+		/* clear the retry state */
+		bp->b_last_error = 0;
+		bp->b_retries = 0;
+		bp->b_first_retry_time = 0;
+
+		/*
+		 * Note that for things like remote attribute buffers, there may
+		 * not be a buffer log item here, so processing the buffer log
+		 * item must remain optional.
+		 */
+		if (bp->b_log_item)
+			xfs_buf_item_done(bp);
+
+		if (bp->b_iodone)
+			bp->b_iodone(bp);
+	}
+
+	xfs_buf_clear_flags(bp, XBF_READ | XBF_WRITE | XBF_READ_AHEAD);
+	if (async)
+		xfs_buf_relse(bp);
+}
+
+static void
+xfs_buf_ioend_work(
+	struct work_struct	*work)
+{
+	xfs_buf_ioend(container_of(work, struct xfs_buf, b_ioend_work));
+}
+
+void
+__xfs_buf_ioerror(
+	struct xfs_buf		*bp,
+	int			error,
+	xfs_failaddr_t		failaddr)
+{
+	ASSERT(error <= 0 && error >= -1000);
+	bp->b_error = error;
+	trace_xfs_buf_ioerror(bp, error, failaddr);
+}
+
+void
+xfs_buf_ioerror_alert(
+	struct xfs_buf		*bp,
+	xfs_failaddr_t		func)
+{
+	xfs_buf_alert_ratelimited(bp, "XFS: metadata IO error",
+		"metadata I/O error in \"%pS\" at daddr 0x%llx len %d error %d",
+				  func, (uint64_t)xfs_buf_daddr(bp),
+				  bp->b_length, -bp->b_error);
+}
+
+/*
+ * Fail a locked and referenced buffer outside the I/O path.
+ *
+ * The caller transfers a reference which will be released after processing the
+ * error.
+ */
+void
+xfs_buf_fail(
+	struct xfs_buf	*bp)
+{
+	ASSERT(xfs_buf_islocked(bp));
+
+	xfs_buf_set_flags(bp, XBF_ASYNC);
+	xfs_buf_clear_flags(bp, XBF_DONE);
+	xfs_buf_stale(bp);
+	xfs_buf_ioerror(bp, -EIO);
+	xfs_buf_ioend(bp);
+}
+
+int
+xfs_bwrite(
+	struct xfs_buf		*bp)
+{
+	int			error;
+
+	ASSERT(xfs_buf_islocked(bp));
+
+	xfs_buf_set_flags(bp, XBF_WRITE);
+	xfs_buf_clear_flags(bp, XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q |
+				XBF_DONE);
+
+	xfs_buf_submit(bp);
+	error = xfs_buf_iowait(bp);
+	if (error)
+		xfs_force_shutdown(bp->b_mount, SHUTDOWN_META_IO_ERROR);
+	return error;
+}
+
+static void
+xfs_buf_bio_end_io(
+	struct bio		*bio)
+{
+	struct xfs_buf		*bp = bio->bi_private;
+
+	if (bio->bi_status)
+		xfs_buf_ioerror(bp, blk_status_to_errno(bio->bi_status));
+	else if ((bp->b_flags & XBF_WRITE) && (bp->b_flags & XBF_ASYNC) &&
+		 XFS_TEST_ERROR(bp->b_mount, XFS_ERRTAG_BUF_IOERROR))
+		xfs_buf_ioerror(bp, -EIO);
+
+	if (bp->b_flags & XBF_ASYNC) {
+		INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
+		queue_work(bp->b_mount->m_buf_workqueue, &bp->b_ioend_work);
+	} else {
+		complete(&bp->b_iowait);
+	}
+
+	bio_put(bio);
+}
+
+static inline blk_opf_t
+xfs_buf_bio_op(
+	struct xfs_buf		*bp)
+{
+	blk_opf_t		op;
+
+	if (bp->b_flags & XBF_WRITE) {
+		op = REQ_OP_WRITE;
+	} else {
+		op = REQ_OP_READ;
+		if (bp->b_flags & XBF_READ_AHEAD)
+			op |= REQ_RAHEAD;
+	}
+
+	return op | REQ_META;
+}
+
+static void
+xfs_buf_submit_bio(
+	struct xfs_buf		*bp)
+{
+	unsigned int		len = BBTOB(bp->b_length);
+	unsigned int		nr_vecs = bio_add_max_vecs(bp->b_addr, len);
+	unsigned int		map = 0;
+	struct blk_plug		plug;
+	struct bio		*bio;
+
+	bio = bio_alloc(bp->b_target->bt_bdev, nr_vecs, xfs_buf_bio_op(bp),
+			GFP_NOIO);
+	if (is_vmalloc_addr(bp->b_addr))
+		bio_add_vmalloc(bio, bp->b_addr, len);
+	else
+		bio_add_virt_nofail(bio, bp->b_addr, len);
+	bio->bi_private = bp;
+	bio->bi_end_io = xfs_buf_bio_end_io;
+
+	/*
+	 * If there is more than one map segment, split out a new bio for each
+	 * map except of the last one.  The last map is handled by the
+	 * remainder of the original bio outside the loop.
+	 */
+	blk_start_plug(&plug);
+	for (map = 0; map < bp->b_map_count - 1; map++) {
+		struct bio	*split;
+
+		split = bio_split(bio, bp->b_maps[map].bm_len, GFP_NOFS,
+				&fs_bio_set);
+		split->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
+		bio_chain(split, bio);
+		submit_bio(split);
+	}
+	bio->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
+	submit_bio(bio);
+	blk_finish_plug(&plug);
+}
+
+/*
+ * Wait for I/O completion of a sync buffer and return the I/O error code.
+ */
+static int
+xfs_buf_iowait(
+	struct xfs_buf	*bp)
+{
+	ASSERT(!(bp->b_flags & XBF_ASYNC));
+
+	trace_xfs_buf_iowait(bp, _RET_IP_);
+	wait_for_completion(&bp->b_iowait);
+	trace_xfs_buf_iowait_done(bp, _RET_IP_);
+
+	xfs_buf_ioend(bp);
+	return bp->b_error;
+}
+
+/*
+ * Run the write verifier callback function if it exists. If this fails, mark
+ * the buffer with an error and do not dispatch the I/O.
+ */
+static bool
+xfs_buf_verify_write(
+	struct xfs_buf		*bp)
+{
+	if (bp->b_ops) {
+		bp->b_ops->verify_write(bp);
+		if (bp->b_error)
+			return false;
+	} else if (bp->b_rhash_key != XFS_BUF_DADDR_NULL) {
+		/*
+		 * Non-crc filesystems don't attach verifiers during log
+		 * recovery, so don't warn for such filesystems.
+		 */
+		if (xfs_has_crc(bp->b_mount)) {
+			xfs_warn(bp->b_mount,
+				"%s: no buf ops on daddr 0x%llx len %d",
+				__func__, xfs_buf_daddr(bp),
+				bp->b_length);
+			xfs_hex_dump(bp->b_addr, XFS_CORRUPTION_DUMP_LEN);
+			dump_stack();
+		}
+	}
+
+	return true;
+}
+
+/*
+ * Buffer I/O submission path, read or write. Asynchronous submission transfers
+ * the buffer lock ownership and the current reference to the IO. It is not
+ * safe to reference the buffer after a call to this function unless the caller
+ * holds an additional reference itself.
+ */
+static void
+xfs_buf_submit(
+	struct xfs_buf	*bp)
+{
+	trace_xfs_buf_submit(bp, _RET_IP_);
+
+	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+
+	/*
+	 * On log shutdown we stale and complete the buffer immediately. We can
+	 * be called to read the superblock before the log has been set up, so
+	 * be careful checking the log state.
+	 *
+	 * Checking the mount shutdown state here can result in the log tail
+	 * moving inappropriately on disk as the log may not yet be shut down.
+	 * i.e. failing this buffer on mount shutdown can remove it from the AIL
+	 * and move the tail of the log forwards without having written this
+	 * buffer to disk. This corrupts the log tail state in memory, and
+	 * because the log may not be shut down yet, it can then be propagated
+	 * to disk before the log is shutdown. Hence we check log shutdown
+	 * state here rather than mount state to avoid corrupting the log tail
+	 * on shutdown.
+	 */
+	if (bp->b_mount->m_log && xlog_is_shutdown(bp->b_mount->m_log)) {
+		xfs_buf_ioerror(bp, -EIO);
+		goto ioerror;
+	}
+
+	if (bp->b_flags & XBF_WRITE)
+		xfs_buf_wait_unpin(bp);
+
+	/*
+	 * Make sure we capture only current IO errors rather than stale errors
+	 * left over from previous use of the buffer (e.g. failed readahead).
+	 */
+	bp->b_error = 0;
+
+	if ((bp->b_flags & XBF_WRITE) && !xfs_buf_verify_write(bp)) {
+		/* ->verify_write should have set b_error already */
+		xfs_force_shutdown(bp->b_mount, SHUTDOWN_CORRUPT_INCORE);
+		goto ioerror;
+	}
+
+	/* In-memory targets are directly mapped, no I/O required. */
+	if (xfs_buftarg_is_mem(bp->b_target))
+		goto end_io;
+
+	xfs_buf_submit_bio(bp);
+	return;
+
+ioerror:
+	xfs_buf_clear_flags(bp, XBF_DONE);
+	xfs_buf_stale(bp);
+end_io:
+	if (bp->b_flags & XBF_ASYNC)
+		xfs_buf_ioend(bp);
+	else
+		complete(&bp->b_iowait);
+}
+
+/*
+ * Log a message about and stale a buffer that a caller has decided is corrupt.
+ *
+ * This function should be called for the kinds of metadata corruption that
+ * cannot be detect from a verifier, such as incorrect inter-block relationship
+ * data.  Do /not/ call this function from a verifier function.
+ *
+ * The buffer must be XBF_DONE prior to the call.  Afterwards, the buffer will
+ * be marked stale, but b_error will not be set.  The caller is responsible for
+ * releasing the buffer or fixing it.
+ */
+void
+__xfs_buf_mark_corrupt(
+	struct xfs_buf		*bp,
+	xfs_failaddr_t		fa)
+{
+	ASSERT(bp->b_flags & XBF_DONE);
+
+	xfs_buf_corruption_error(bp, fa);
+	xfs_buf_stale(bp);
+}
+
+/*
+ *	Handling of buffer targets (buftargs).
+ */
+
+/*
+ * Wait for any bufs with callbacks that have been submitted but have not yet
+ * returned. These buffers will have an elevated hold count, so wait on those
+ * while freeing all the buffers only held by the LRU.
+ */
+static enum lru_status
+xfs_buftarg_drain_rele(
+	struct list_head	*item,
+	struct list_lru_one	*lru,
+	void			*arg)
+
+{
+	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
+	struct list_head	*dispose = arg;
+
+	if (!spin_trylock(&bp->b_lockref.lock))
+		return LRU_SKIP;
+	if (bp->b_lockref.count > 0) {
+		/* need to wait, so skip it this pass */
+		spin_unlock(&bp->b_lockref.lock);
+		trace_xfs_buf_drain_buftarg(bp, _RET_IP_);
+		return LRU_SKIP;
+	}
+
+	xfs_buf_kill(bp);
+	list_lru_isolate_move(lru, item, dispose);
+	spin_unlock(&bp->b_lockref.lock);
+	return LRU_REMOVED;
+}
+
+/*
+ * Wait for outstanding I/O on the buftarg to complete.
+ */
+void
+xfs_buftarg_wait(
+	struct xfs_buftarg	*btp)
+{
+	/*
+	 * First wait for all in-flight readahead buffers to be released.  This is
+	 * critical as new buffers do not make the LRU until they are released.
+	 *
+	 * Next, flush the buffer workqueue to ensure all completion processing
+	 * has finished. Just waiting on buffer locks is not sufficient for
+	 * async IO as the reference count held over IO is not released until
+	 * after the buffer lock is dropped. Hence we need to ensure here that
+	 * all reference counts have been dropped before we start walking the
+	 * LRU list.
+	 */
+	while (percpu_counter_sum(&btp->bt_readahead_count))
+		delay(100);
+	flush_workqueue(btp->bt_mount->m_buf_workqueue);
+}
+
+void
+xfs_buftarg_drain(
+	struct xfs_buftarg	*btp)
+{
+	LIST_HEAD(dispose);
+	int			loop = 0;
+	bool			write_fail = false;
+
+	xfs_buftarg_wait(btp);
+
+	/* loop until there is nothing left on the lru list. */
+	while (list_lru_count(&btp->bt_lru)) {
+		list_lru_walk(&btp->bt_lru, xfs_buftarg_drain_rele,
+			      &dispose, LONG_MAX);
+
+		while (!list_empty(&dispose)) {
+			struct xfs_buf *bp;
+			bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
+			list_del_init(&bp->b_lru);
+			if (bp->b_flags & XBF_WRITE_FAIL) {
+				write_fail = true;
+				xfs_buf_alert_ratelimited(bp,
+					"XFS: Corruption Alert",
+"Corruption Alert: Buffer at daddr 0x%llx had permanent write failures!",
+					(long long)xfs_buf_daddr(bp));
+			}
+			xfs_buf_destroy(bp);
+		}
+		if (loop++ != 0)
+			delay(100);
+	}
+
+	/*
+	 * If one or more failed buffers were freed, that means dirty metadata
+	 * was thrown away. This should only ever happen after I/O completion
+	 * handling has elevated I/O error(s) to permanent failures and shuts
+	 * down the journal.
+	 */
+	if (write_fail) {
+		ASSERT(xlog_is_shutdown(btp->bt_mount->m_log));
+		xfs_alert(btp->bt_mount,
+	      "Please run xfs_repair to determine the extent of the problem.");
+	}
+}
+
+static enum lru_status
+xfs_buftarg_isolate(
+	struct list_head	*item,
+	struct list_lru_one	*lru,
+	void			*arg)
+{
+	struct xfs_buf		*bp = container_of(item, struct xfs_buf, b_lru);
+	struct list_head	*dispose = arg;
+
+	/*
+	 * We are inverting the lru lock vs bp->b_lockref.lock order here, so
+	 * use a trylock.  If we fail to get the lock, just skip the buffer.
+	 */
+	if (!spin_trylock(&bp->b_lockref.lock))
+		return LRU_SKIP;
+
+	/*
+	 * If the buffer is in use, remove it from the LRU for now.  We can't
+	 * free it while someone is using it, and we should also not count
+	 * eviction passed for it, just as if it hadn't been added to the LRU
+	 * yet.
+	 */
+	if (bp->b_lockref.count > 0) {
+		list_lru_isolate(lru, &bp->b_lru);
+		spin_unlock(&bp->b_lockref.lock);
+		return LRU_REMOVED;
+	}
+
+	/*
+	 * Decrement the b_lru_ref count unless the value is already
+	 * zero. If the value is already zero, we need to reclaim the
+	 * buffer, otherwise it gets another trip through the LRU.
+	 */
+	if (atomic_add_unless(&bp->b_lru_ref, -1, 0)) {
+		spin_unlock(&bp->b_lockref.lock);
+		return LRU_ROTATE;
+	}
+
+	xfs_buf_kill(bp);
+	list_lru_isolate_move(lru, item, dispose);
+	spin_unlock(&bp->b_lockref.lock);
+	return LRU_REMOVED;
+}
+
+static unsigned long
+xfs_buftarg_shrink_scan(
+	struct shrinker		*shrink,
+	struct shrink_control	*sc)
+{
+	struct xfs_buftarg	*btp = shrink->private_data;
+	LIST_HEAD(dispose);
+	unsigned long		freed;
+
+	freed = list_lru_shrink_walk(&btp->bt_lru, sc,
+				     xfs_buftarg_isolate, &dispose);
+
+	while (!list_empty(&dispose)) {
+		struct xfs_buf *bp;
+		bp = list_first_entry(&dispose, struct xfs_buf, b_lru);
+		list_del_init(&bp->b_lru);
+		xfs_buf_destroy(bp);
+	}
+
+	return freed;
+}
+
+static unsigned long
+xfs_buftarg_shrink_count(
+	struct shrinker		*shrink,
+	struct shrink_control	*sc)
+{
+	struct xfs_buftarg	*btp = shrink->private_data;
+	return list_lru_shrink_count(&btp->bt_lru, sc);
+}
+
+void
+xfs_destroy_buftarg(
+	struct xfs_buftarg	*btp)
+{
+	shrinker_free(btp->bt_shrinker);
+	ASSERT(percpu_counter_sum(&btp->bt_readahead_count) == 0);
+	percpu_counter_destroy(&btp->bt_readahead_count);
+	list_lru_destroy(&btp->bt_lru);
+	rhashtable_destroy(&btp->bt_hash);
+}
+
+void
+xfs_free_buftarg(
+	struct xfs_buftarg	*btp)
+{
+	xfs_destroy_buftarg(btp);
+	fs_put_dax(btp->bt_daxdev, btp->bt_mount);
+	/* the main block device is closed by kill_block_super */
+	if (btp->bt_bdev != btp->bt_mount->m_super->s_bdev)
+		fs_bdev_file_release(btp->bt_file, btp->bt_mount->m_super);
+	kfree(btp);
+}
+
+/*
+ * Configure this buffer target for hardware-assisted atomic writes if the
+ * underlying block device supports is congruent with the filesystem geometry.
+ */
+static inline void
+xfs_configure_buftarg_atomic_writes(
+	struct xfs_buftarg	*btp)
+{
+	struct xfs_mount	*mp = btp->bt_mount;
+	unsigned int		min_bytes, max_bytes;
+
+	min_bytes = bdev_atomic_write_unit_min_bytes(btp->bt_bdev);
+	max_bytes = bdev_atomic_write_unit_max_bytes(btp->bt_bdev);
+
+	/*
+	 * Ignore atomic write geometry that is nonsense or doesn't even cover
+	 * a single fsblock.
+	 */
+	if (min_bytes > max_bytes ||
+	    min_bytes > mp->m_sb.sb_blocksize ||
+	    max_bytes < mp->m_sb.sb_blocksize) {
+		min_bytes = 0;
+		max_bytes = 0;
+	}
+
+	btp->bt_awu_min = min_bytes;
+	btp->bt_awu_max = max_bytes;
+}
+
+/* Configure a buffer target that abstracts a block device. */
+int
+xfs_configure_buftarg(
+	struct xfs_buftarg	*btp,
+	unsigned int		sectorsize,
+	xfs_rfsblock_t		nr_blocks)
+{
+	struct xfs_mount	*mp = btp->bt_mount;
+
+	if (btp->bt_bdev) {
+		int		error;
+
+		error = bdev_validate_blocksize(btp->bt_bdev, sectorsize);
+		if (error) {
+			xfs_warn(mp,
+				"Cannot use blocksize %u on device %pg, err %d",
+				sectorsize, btp->bt_bdev, error);
+			return -EINVAL;
+		}
+
+		if (bdev_can_atomic_write(btp->bt_bdev))
+			xfs_configure_buftarg_atomic_writes(btp);
+	}
+
+	btp->bt_meta_sectorsize = sectorsize;
+	btp->bt_meta_sectormask = sectorsize - 1;
+	/* m_blkbb_log is not set up yet */
+	btp->bt_nr_sectors = nr_blocks << (mp->m_sb.sb_blocklog - BBSHIFT);
+	return 0;
+}
+
+int
+xfs_init_buftarg(
+	struct xfs_buftarg		*btp,
+	size_t				logical_sectorsize,
+	const char			*descr)
+{
+	/* The maximum size of the buftarg is only known once the sb is read. */
+	btp->bt_nr_sectors = XFS_BUF_DADDR_MAX;
+
+	/* Set up device logical sector size mask */
+	btp->bt_logical_sectorsize = logical_sectorsize;
+	btp->bt_logical_sectormask = logical_sectorsize - 1;
+
+	/*
+	 * Buffer IO error rate limiting. Limit it to no more than 10 messages
+	 * per 30 seconds so as to not spam logs too much on repeated errors.
+	 */
+	ratelimit_state_init(&btp->bt_ioerror_rl, 30 * HZ,
+			     DEFAULT_RATELIMIT_BURST);
+
+	if (rhashtable_init(&btp->bt_hash, &xfs_buf_hash_params))
+		return -ENOMEM;
+	if (list_lru_init(&btp->bt_lru))
+		goto out_destroy_hash;
+	if (percpu_counter_init(&btp->bt_readahead_count, 0, GFP_KERNEL))
+		goto out_destroy_lru;
+
+	btp->bt_shrinker =
+		shrinker_alloc(SHRINKER_NUMA_AWARE, "xfs-buf:%s", descr);
+	if (!btp->bt_shrinker)
+		goto out_destroy_io_count;
+	btp->bt_shrinker->count_objects = xfs_buftarg_shrink_count;
+	btp->bt_shrinker->scan_objects = xfs_buftarg_shrink_scan;
+	btp->bt_shrinker->private_data = btp;
+	shrinker_register(btp->bt_shrinker);
+	return 0;
+
+out_destroy_io_count:
+	percpu_counter_destroy(&btp->bt_readahead_count);
+out_destroy_lru:
+	list_lru_destroy(&btp->bt_lru);
+out_destroy_hash:
+	rhashtable_destroy(&btp->bt_hash);
+	return -ENOMEM;
+}
+
+struct xfs_buftarg *
+xfs_alloc_buftarg(
+	struct xfs_mount	*mp,
+	struct file		*bdev_file)
+{
+	struct xfs_buftarg	*btp;
+	const struct dax_holder_operations *ops = NULL;
+	int			error;
+
+
+#if defined(CONFIG_FS_DAX) && defined(CONFIG_MEMORY_FAILURE)
+	ops = &xfs_dax_holder_operations;
+#endif
+	btp = kzalloc_obj(*btp, GFP_KERNEL | __GFP_NOFAIL);
+
+	btp->bt_mount = mp;
+	btp->bt_file = bdev_file;
+	btp->bt_bdev = file_bdev(bdev_file);
+	btp->bt_dev = btp->bt_bdev->bd_dev;
+	btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
+					    mp, ops);
+
+	/*
+	 * Flush and invalidate all devices' pagecaches before reading any
+	 * metadata because XFS doesn't use the bdev pagecache.
+	 */
+	error = sync_blockdev(btp->bt_bdev);
+	if (error)
+		goto error_free;
+
+	/*
+	 * When allocating the buftargs we have not yet read the super block and
+	 * thus don't know the file system sector size yet.
+	 */
+	btp->bt_meta_sectorsize = bdev_logical_block_size(btp->bt_bdev);
+	btp->bt_meta_sectormask = btp->bt_meta_sectorsize - 1;
+
+	error = xfs_init_buftarg(btp, btp->bt_meta_sectorsize,
+				mp->m_super->s_id);
+	if (error)
+		goto error_free;
+
+	return btp;
+
+error_free:
+	fs_put_dax(btp->bt_daxdev, mp);
+	kfree(btp);
+	return ERR_PTR(error);
+}
+
+static inline void
+xfs_buf_list_del(
+	struct xfs_buf		*bp)
+{
+	list_del_init(&bp->b_list);
+	wake_up_var(&bp->b_list);
+}
+
+/*
+ * Cancel a delayed write list.
+ *
+ * Remove each buffer from the list, clear the delwri queue flag and drop the
+ * associated buffer reference.
+ */
+void
+xfs_buf_delwri_cancel(
+	struct list_head	*list)
+{
+	struct xfs_buf		*bp;
+
+	while (!list_empty(list)) {
+		bp = list_first_entry(list, struct xfs_buf, b_list);
+
+		xfs_buf_lock(bp);
+		xfs_buf_clear_flags(bp, _XBF_DELWRI_Q);
+		xfs_buf_list_del(bp);
+		xfs_buf_relse(bp);
+	}
+}
+
+/*
+ * Add a buffer to the delayed write list.
+ *
+ * This queues a buffer for writeout if it hasn't already been.  Note that
+ * neither this routine nor the buffer list submission functions perform
+ * any internal synchronization.  It is expected that the lists are thread-local
+ * to the callers.
+ *
+ * Returns true if we queued up the buffer, or false if it already had
+ * been on the buffer list.
+ */
+bool
+xfs_buf_delwri_queue(
+	struct xfs_buf		*bp,
+	struct list_head	*list)
+{
+	ASSERT(xfs_buf_islocked(bp));
+	ASSERT(!(bp->b_flags & XBF_READ));
+
+	/*
+	 * If the buffer is already marked delwri it already is queued up
+	 * by someone else for imediate writeout.  Just ignore it in that
+	 * case.
+	 */
+	if (bp->b_flags & _XBF_DELWRI_Q) {
+		trace_xfs_buf_delwri_queued(bp, _RET_IP_);
+		return false;
+	}
+
+	trace_xfs_buf_delwri_queue(bp, _RET_IP_);
+
+	/*
+	 * If a buffer gets written out synchronously or marked stale while it
+	 * is on a delwri list we lazily remove it. To do this, the other party
+	 * clears the  _XBF_DELWRI_Q flag but otherwise leaves the buffer alone.
+	 * It remains referenced and on the list.  In a rare corner case it
+	 * might get readded to a delwri list after the synchronous writeout, in
+	 * which case we need just need to re-add the flag here.
+	 */
+	xfs_buf_set_flags(bp, _XBF_DELWRI_Q);
+	if (list_empty(&bp->b_list)) {
+		xfs_buf_hold(bp);
+		list_add_tail(&bp->b_list, list);
+	}
+
+	return true;
+}
+
+/*
+ * Queue a buffer to this delwri list as part of a data integrity operation.
+ * If the buffer is on any other delwri list, we'll wait for that to clear
+ * so that the caller can submit the buffer for IO and wait for the result.
+ * Callers must ensure the buffer is not already on the list.
+ */
+void
+xfs_buf_delwri_queue_here(
+	struct xfs_buf		*bp,
+	struct list_head	*buffer_list)
+{
+	/*
+	 * We need this buffer to end up on the /caller's/ delwri list, not any
+	 * old list.  This can happen if the buffer is marked stale (which
+	 * clears DELWRI_Q) after the AIL queues the buffer to its list but
+	 * before the AIL has a chance to submit the list.
+	 */
+	while (!list_empty(&bp->b_list)) {
+		xfs_buf_unlock(bp);
+		wait_var_event(&bp->b_list, list_empty(&bp->b_list));
+		xfs_buf_lock(bp);
+	}
+
+	ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
+
+	xfs_buf_delwri_queue(bp, buffer_list);
+}
+
+/*
+ * Compare function is more complex than it needs to be because
+ * the return value is only 32 bits and we are doing comparisons
+ * on 64 bit values
+ */
+static int
+xfs_buf_cmp(
+	void			*priv,
+	const struct list_head	*a,
+	const struct list_head	*b)
+{
+	struct xfs_buf	*ap = container_of(a, struct xfs_buf, b_list);
+	struct xfs_buf	*bp = container_of(b, struct xfs_buf, b_list);
+	xfs_daddr_t		diff;
+
+	diff = ap->b_maps[0].bm_bn - bp->b_maps[0].bm_bn;
+	if (diff < 0)
+		return -1;
+	if (diff > 0)
+		return 1;
+	return 0;
+}
+
+static bool
+xfs_buf_delwri_submit_prep(
+	struct xfs_buf		*bp)
+{
+	/*
+	 * Someone else might have written the buffer synchronously or marked it
+	 * stale in the meantime.  In that case only the _XBF_DELWRI_Q flag got
+	 * cleared, and we have to drop the reference and remove it from the
+	 * list here.
+	 */
+	if (!(bp->b_flags & _XBF_DELWRI_Q)) {
+		xfs_buf_list_del(bp);
+		xfs_buf_relse(bp);
+		return false;
+	}
+
+	trace_xfs_buf_delwri_split(bp, _RET_IP_);
+	xfs_buf_clear_flags(bp, _XBF_DELWRI_Q);
+	xfs_buf_set_flags(bp, XBF_WRITE);
+	return true;
+}
+
+/*
+ * Write out a buffer list asynchronously.
+ *
+ * This will take the @buffer_list, write all non-locked and non-pinned buffers
+ * out and not wait for I/O completion on any of the buffers.  This interface
+ * is only safely useable for callers that can track I/O completion by higher
+ * level means, e.g. AIL pushing as the @buffer_list is consumed in this
+ * function.
+ *
+ * Note: this function will skip buffers it would block on, and in doing so
+ * leaves them on @buffer_list so they can be retried on a later pass. As such,
+ * it is up to the caller to ensure that the buffer list is fully submitted or
+ * cancelled appropriately when they are finished with the list. Failure to
+ * cancel or resubmit the list until it is empty will result in leaked buffers
+ * at unmount time.
+ */
+int
+xfs_buf_delwri_submit_nowait(
+	struct list_head	*buffer_list)
+{
+	struct xfs_buf		*bp, *n;
+	int			pinned = 0;
+	struct blk_plug		plug;
+
+	list_sort(NULL, buffer_list, xfs_buf_cmp);
+
+	blk_start_plug(&plug);
+	list_for_each_entry_safe(bp, n, buffer_list, b_list) {
+		if (!xfs_buf_trylock(bp))
+			continue;
+		if (xfs_buf_ispinned(bp)) {
+			xfs_buf_unlock(bp);
+			pinned++;
+			continue;
+		}
+		if (!xfs_buf_delwri_submit_prep(bp))
+			continue;
+		xfs_buf_set_flags(bp, XBF_ASYNC);
+		xfs_buf_list_del(bp);
+		xfs_buf_submit(bp);
+	}
+	blk_finish_plug(&plug);
+
+	return pinned;
+}
+
+/*
+ * Write out a buffer list synchronously.
+ *
+ * This will take the @buffer_list, write all buffers out and wait for I/O
+ * completion on all of the buffers. @buffer_list is consumed by the function,
+ * so callers must have some other way of tracking buffers if they require such
+ * functionality.
+ */
+int
+xfs_buf_delwri_submit(
+	struct list_head	*buffer_list)
+{
+	LIST_HEAD		(wait_list);
+	int			error = 0, error2;
+	struct xfs_buf		*bp, *n;
+	struct blk_plug		plug;
+
+	list_sort(NULL, buffer_list, xfs_buf_cmp);
+
+	blk_start_plug(&plug);
+	list_for_each_entry_safe(bp, n, buffer_list, b_list) {
+		xfs_buf_lock(bp);
+		if (!xfs_buf_delwri_submit_prep(bp))
+			continue;
+		xfs_buf_clear_flags(bp, XBF_ASYNC);
+		list_move_tail(&bp->b_list, &wait_list);
+		xfs_buf_submit(bp);
+	}
+	blk_finish_plug(&plug);
+
+	/* Wait for IO to complete. */
+	while (!list_empty(&wait_list)) {
+		bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
+
+		xfs_buf_list_del(bp);
+
+		/*
+		 * Wait on the locked buffer, check for errors and unlock and
+		 * release the delwri queue reference.
+		 */
+		error2 = xfs_buf_iowait(bp);
+		xfs_buf_relse(bp);
+		if (!error)
+			error = error2;
+	}
+
+	return error;
+}
+
+void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
+{
+	/*
+	 * Set the lru reference count to 0 based on the error injection tag.
+	 * This allows userspace to disrupt buffer caching for debug/testing
+	 * purposes.
+	 */
+	if (XFS_TEST_ERROR(bp->b_mount, XFS_ERRTAG_BUF_LRU_REF))
+		lru_ref = 0;
+
+	atomic_set(&bp->b_lru_ref, lru_ref);
+}
+
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure. The verifier magic is in disk byte order so the caller is
+ * expected to pass the value directly from disk.
+ */
+bool
+xfs_verify_magic(
+	struct xfs_buf		*bp,
+	__be32			dmagic)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	int			idx;
+
+	idx = xfs_has_crc(mp);
+	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic[idx]))
+		return false;
+	return dmagic == bp->b_ops->magic[idx];
+}
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure. The verifier magic is in disk byte order so the caller is
+ * expected to pass the value directly from disk.
+ */
+bool
+xfs_verify_magic16(
+	struct xfs_buf		*bp,
+	__be16			dmagic)
+{
+	struct xfs_mount	*mp = bp->b_mount;
+	int			idx;
+
+	idx = xfs_has_crc(mp);
+	if (WARN_ON(!bp->b_ops || !bp->b_ops->magic16[idx]))
+		return false;
+	return dmagic == bp->b_ops->magic16[idx];
+}