[PATCH RFC 2/2] xfs: drop xa_lock around log force in xfs_buf_item push

[Brian Foster]

If the trylock fails and the buffer is pinned and stale, the
resulting xfs_log_force() can lead to lock recursion on the ailp
xa_lock. Call __xfs_buf_trylock() to attempt the buf lock with
xa_lock held, but to avoid the log force. We subsequently pull the
check and log force up into xfs_buf_item_push() where we can drop
and reacquire xa_lock appropriately.

Signed-off-by: Brian Foster <bfoster at redhat.com>
---
 fs/xfs/xfs_buf_item.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/fs/xfs/xfs_buf_item.c b/fs/xfs/xfs_buf_item.c
index 9c4c050..7b6e98a 100644
--- a/fs/xfs/xfs_buf_item.c
+++ b/fs/xfs/xfs_buf_item.c
@@ -469,8 +469,16 @@ xfs_buf_item_push(
 
 	if (xfs_buf_ispinned(bp))
 		return XFS_ITEM_PINNED;
-	if (!xfs_buf_trylock(bp))
+
+	if (!__xfs_buf_trylock(bp, false)) {
+		if (atomic_read(&bp->b_pin_count) &&
+		    (bp->b_flags & XBF_STALE)) {
+			spin_unlock(&lip->li_ailp->xa_lock);
+			xfs_log_force(bp->b_target->bt_mount, 0);
+			spin_lock(&lip->li_ailp->xa_lock);
+		}
 		return XFS_ITEM_LOCKED;
+	}
 
 	ASSERT(!(bip->bli_flags & XFS_BLI_STALE));
 
-- 
1.7.7.6