From: Dave Chinner <dchinner@xxxxxxxxxx>
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
encoded via ERR_PTR() 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.
Finally, to ensure code outside the buffer cache does not see any
change, convert external callers to use xfs_incore() and change that
to an inline function that maintains the old "buffer or NULL" return
values so the external code doesn't need to care about this internal
change to _xfs_buf_find() semantics.
Signed-Off-By: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_buf.c | 56 +++++++++++++++++++++++++++++++++++++++++---------------
fs/xfs/xfs_buf.h | 8 +++++++-
fs/xfs/xfs_qm.c | 5 ++---
3 files changed, 50 insertions(+), 19 deletions(-)
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 88587b33dd15..fa1e62ac5e8c 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -549,20 +549,32 @@ xfs_buf_hash_destroy(
}
/*
- * Look up, and creates 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.
+ *
+ * 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
+ * NULL if we fail to find a match and @new_bp was NULL
+ * @new_bp if we inserted it into the cache
+ * the buffer we found and locked.
*/
-xfs_buf_t *
+
+struct xfs_buf *
_xfs_buf_find(
struct xfs_buftarg *btp,
struct xfs_buf_map *map,
int nmaps,
xfs_buf_flags_t flags,
- xfs_buf_t *new_bp)
+ struct xfs_buf *new_bp)
{
struct xfs_perag *pag;
- xfs_buf_t *bp;
+ struct xfs_buf *bp;
struct xfs_buf_map cmap = { .bm_bn = map[0].bm_bn };
xfs_daddr_t eofs;
int i;
@@ -580,16 +592,11 @@ _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 ERR_PTR(-EFSCORRUPTED);
}
pag = xfs_perag_get(btp->bt_mount,
@@ -626,7 +633,7 @@ _xfs_buf_find(
if (flags & XBF_TRYLOCK) {
xfs_buf_rele(bp);
XFS_STATS_INC(btp->bt_mount, xb_busy_locked);
- return NULL;
+ return ERR_PTR(-EAGAIN);
}
xfs_buf_lock(bp);
XFS_STATS_INC(btp->bt_mount, xb_get_locked_waited);
@@ -666,9 +673,28 @@ xfs_buf_get_map(
int error = 0;
bp = _xfs_buf_find(target, map, nmaps, flags, NULL);
- if (likely(bp))
+ if (!IS_ERR_OR_NULL(bp))
goto found;
+ switch (PTR_ERR(bp)) {
+ case 0:
+ /* cache miss, need to insert new buffer */
+ break;
+
+ case -EAGAIN:
+ /* cache hit, trylock failure, caller handles failure */
+ ASSERT(flags & XBF_TRYLOCK);
+ return NULL;
+
+ 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))
return NULL;
@@ -680,7 +706,7 @@ xfs_buf_get_map(
}
bp = _xfs_buf_find(target, map, nmaps, flags, new_bp);
- if (!bp) {
+ if (IS_ERR_OR_NULL(bp)) {
xfs_buf_free(new_bp);
return NULL;
}
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 2f4c91452861..db87ad0b9b79 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -229,8 +229,14 @@ xfs_incore(
size_t numblks,
xfs_buf_flags_t flags)
{
+ struct xfs_buf *bp;
+
DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
- return _xfs_buf_find(target, &map, 1, flags, NULL);
+
+ bp = _xfs_buf_find(target, &map, 1, flags, NULL);
+ if (IS_ERR_OR_NULL(bp))
+ return NULL;
+ return bp;
}
struct xfs_buf *_xfs_buf_alloc(struct xfs_buftarg *target,
diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 5b848f4b637f..8d90d19684a7 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -1249,9 +1249,8 @@ xfs_qm_flush_one(
*/
if (!xfs_dqflock_nowait(dqp)) {
/* buf is pinned in-core by delwri list */
- DEFINE_SINGLE_BUF_MAP(map, dqp->q_blkno,
- mp->m_quotainfo->qi_dqchunklen);
- bp = _xfs_buf_find(mp->m_ddev_targp, &map, 1, 0, NULL);
+ bp = xfs_incore(mp->m_ddev_targp, dqp->q_blkno,
+ mp->m_quotainfo->qi_dqchunklen, 0);
if (!bp) {
error = -EINVAL;
goto out_unlock;
--
2.16.1
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