[PATCH v3 1/2] xfs: recheck buffer pinned status after push trylock failure

[Brian Foster]

The buffer pinned check and trylock sequence in xfs_buf_item_push()
can race with an active transaction on marking the buffer pinned.
This can result in the buffer becoming pinned and stale after the
initial check and the trylock failure, but before the check in
xfs_buf_trylock() that issues a log force. If the log force is
issued from this context, a spinlock recursion occurs on xa_lock.

Prepare xfs_buf_item_push() to handle the race by detecting a
pinned buffer after the trylock failure so xfsaild issues a log
force from a safe context. This, along with various previous fixes,
renders the log force in xfs_buf_trylock() redundant.

Signed-off-by: Brian Foster <bfoster at redhat.com>
---
 fs/xfs/xfs_buf_item.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 9c4c050..4e3a059 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -469,8 +469,15 @@ xfs_buf_item_push(
 
 	if (xfs_buf_ispinned(bp))
 		return XFS_ITEM_PINNED;
-	if (!xfs_buf_trylock(bp))
+	if (!xfs_buf_trylock(bp)) {
+		/*
+		 * Check whether we've raced with the buffer being pinned so
+		 * xfsaild will pend up a log force.
+		 */
+		if (xfs_buf_ispinned(bp))
+			return XFS_ITEM_PINNED;
 		return XFS_ITEM_LOCKED;
+	}
 
 	ASSERT(!(bip->bli_flags & XFS_BLI_STALE));
 
-- 
1.7.7.6