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Commit b027d4c9 authored by Dave Chinner's avatar Dave Chinner Committed by Darrick J. Wong
Browse files

xfs: don't retry xfs_buf_find on XBF_TRYLOCK failure 



When looking at an event trace recently, I noticed that non-blocking
buffer lookup attempts would fail on cached locked buffers and then
run the slow cache-miss path. This means we are doing an xfs_buf
allocation, lookup and free unnecessarily every time we avoid
blocking on a locked buffer.

Fix this by changing _xfs_buf_find() to return an error status to
the caller to indicate that we failed the lock attempt rather than
just returning a NULL. This allows the higher level code to
discriminate between a cache miss and an cache hit that we failed to
lock.

This also allows us to return a -EFSCORRUPTED state if we are asked
to look up a block number outside the range of the filesystem in
_xfs_buf_find(), which moves us one step closer to being able to
handle such errors in a more graceful manner at the higher levels.

Signed-Off-By: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarCarlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 8925a3dc

fs/xfs/xfs_buf.c

+65 −28
Original line number Diff line number Diff line
@@ -549,17 +549,31 @@ xfs_buf_hash_destroy( 
}



/*

 * Look up (and insert if absent), a lockable buffer for a given

 * range of an inode.  The buffer is returned locked. No I/O is

 * implied by this call.

 * Look up a buffer in the buffer cache and return it referenced and locked

 * in @found_bp.

 *

 * If @new_bp is supplied and we have a lookup miss, insert @new_bp into the

 * cache.

 *

 * If XBF_TRYLOCK is set in @flags, only try to lock the buffer and return

 * -EAGAIN if we fail to lock it.

 *

 * Return values are:

 *	-EFSCORRUPTED if have been supplied with an invalid address

 *	-EAGAIN on trylock failure

 *	-ENOENT if we fail to find a match and @new_bp was NULL

 *	0, with @found_bp:

 *		- @new_bp if we inserted it into the cache

 *		- the buffer we found and locked.

 */

static struct xfs_buf *

_xfs_buf_find(

static int

xfs_buf_find(

	struct xfs_buftarg	*btp,

	struct xfs_buf_map	*map,

	int			nmaps,

	xfs_buf_flags_t		flags,

	struct xfs_buf		*new_bp)

	struct xfs_buf		*new_bp,

	struct xfs_buf		**found_bp)

{

	struct xfs_perag	*pag;

	xfs_buf_t		*bp;
@@ -567,6 +581,8 @@ _xfs_buf_find( 
	xfs_daddr_t		eofs;

	int			i;



	*found_bp = NULL;



	for (i = 0; i < nmaps; i++)

		cmap.bm_len += map[i].bm_len;
@@ -580,16 +596,11 @@ _xfs_buf_find( 
	 */

	eofs = XFS_FSB_TO_BB(btp->bt_mount, btp->bt_mount->m_sb.sb_dblocks);

	if (cmap.bm_bn < 0 || cmap.bm_bn >= eofs) {

		/*

		 * XXX (dgc): we should really be returning -EFSCORRUPTED here,

		 * but none of the higher level infrastructure supports

		 * returning a specific error on buffer lookup failures.

		 */

		xfs_alert(btp->bt_mount,

			  "%s: daddr 0x%llx out of range, EOFS 0x%llx",

			  __func__, cmap.bm_bn, eofs);

		WARN_ON(1);

		return NULL;

		return -EFSCORRUPTED;

	}



	pag = xfs_perag_get(btp->bt_mount,
@@ -604,19 +615,20 @@ _xfs_buf_find( 
	}



	/* No match found */

	if (new_bp) {

		/* the buffer keeps the perag reference until it is freed */

		new_bp->b_pag = pag;

		rhashtable_insert_fast(&pag->pag_buf_hash,

				       &new_bp->b_rhash_head,

				       xfs_buf_hash_params);

		spin_unlock(&pag->pag_buf_lock);

	} else {

	if (!new_bp) {

		XFS_STATS_INC(btp->bt_mount, xb_miss_locked);

		spin_unlock(&pag->pag_buf_lock);

		xfs_perag_put(pag);

		return -ENOENT;

	}

	return new_bp;



	/* the buffer keeps the perag reference until it is freed */

	new_bp->b_pag = pag;

	rhashtable_insert_fast(&pag->pag_buf_hash, &new_bp->b_rhash_head,

			       xfs_buf_hash_params);

	spin_unlock(&pag->pag_buf_lock);

	*found_bp = new_bp;

	return 0;



found:

	spin_unlock(&pag->pag_buf_lock);
@@ -626,7 +638,7 @@ _xfs_buf_find( 
		if (flags & XBF_TRYLOCK) {

			xfs_buf_rele(bp);

			XFS_STATS_INC(btp->bt_mount, xb_busy_locked);

			return NULL;

			return -EAGAIN;

		}

		xfs_buf_lock(bp);

		XFS_STATS_INC(btp->bt_mount, xb_get_locked_waited);
@@ -646,7 +658,8 @@ _xfs_buf_find( 


	trace_xfs_buf_find(bp, flags, _RET_IP_);

	XFS_STATS_INC(btp->bt_mount, xb_get_locked);

	return bp;

	*found_bp = bp;

	return 0;

}



struct xfs_buf *
@@ -656,8 +669,14 @@ xfs_buf_incore( 
	size_t			numblks,

	xfs_buf_flags_t		flags)

{

	struct xfs_buf		*bp;

	int			error;

	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);

	return _xfs_buf_find(target, &map, 1, flags, NULL);



	error = xfs_buf_find(target, &map, 1, flags, NULL, &bp);

	if (error)

		return NULL;

	return bp;

}



/*
@@ -676,9 +695,27 @@ xfs_buf_get_map( 
	struct xfs_buf		*new_bp;

	int			error = 0;



	bp = _xfs_buf_find(target, map, nmaps, flags, NULL);

	if (likely(bp))

	error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp);



	switch (error) {

	case 0:

		/* cache hit */

		goto found;

	case -EAGAIN:

		/* cache hit, trylock failure, caller handles failure */

		ASSERT(flags & XBF_TRYLOCK);

		return NULL;

	case -ENOENT:

		/* cache miss, go for insert */

		break;

	case -EFSCORRUPTED:

	default:

		/*

		 * None of the higher layers understand failure types

		 * yet, so return NULL to signal a fatal lookup error.

		 */

		return NULL;

	}



	new_bp = _xfs_buf_alloc(target, map, nmaps, flags);

	if (unlikely(!new_bp))
@@ -690,8 +727,8 @@ xfs_buf_get_map( 
		return NULL;

	}



	bp = _xfs_buf_find(target, map, nmaps, flags, new_bp);

	if (!bp) {

	error = xfs_buf_find(target, map, nmaps, flags, new_bp, &bp);

	if (error) {

		xfs_buf_free(new_bp);

		return NULL;

	}