From: Dave Chinner <dchinner@xxxxxxxxxx>
truncate_setsize() removes pages from the page cache, and hence
requires page locks to be held. It is not valid to lock a page cache
page inside a transaction context as we can hold page locks when we
we reserve space for a transaction. If we do, then we expose an ABBA
deadlock between log space reservation and page locks.
That is, both the write path and writeback lock a page, then start a
transaction for block allocation, which means they can block waiting
for a log reservation with the page lock held. If we hold a log
reservation and then do something that locks a page (e.g.
truncate_setsize in xfs_setattr_size) then that page lock can block
on the page locked and waiting for a log reservation. If the
transaction that is waiting for the page lock is the only active
transaction in the system that can free log space via a commit,
then writeback will never make progress and so log space will never
free up.
This issue with xfs_setattr_size() was introduced back in 2010 by
commit fa9b227 ("xfs: new truncate sequence") which moved the page
cache truncate from outside the transaction context (what was
xfs_itruncate_data()) to inside the transaction context as a call to
truncate_setsize().
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_iops.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ef1ca01..84db577 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -808,22 +808,25 @@ xfs_setattr_size(
*/
inode_dio_wait(inode);
+ /*
+ * Do all the page cache truncate work outside the transaction
+ * context as the "lock" order is page lock->log space reservation.
+ * i.e. locking pages inside the transaction can ABBA deadlock with
+ * writeback.
+ */
error = -block_truncate_page(inode->i_mapping, newsize, xfs_get_blocks);
if (error)
return error;
+ truncate_setsize(inode, newsize);
tp = xfs_trans_alloc(mp, XFS_TRANS_SETATTR_SIZE);
error = xfs_trans_reserve(tp, &M_RES(mp)->tr_itruncate, 0, 0);
if (error)
goto out_trans_cancel;
- truncate_setsize(inode, newsize);
-
commit_flags = XFS_TRANS_RELEASE_LOG_RES;
lock_flags |= XFS_ILOCK_EXCL;
-
xfs_ilock(ip, XFS_ILOCK_EXCL);
-
xfs_trans_ijoin(tp, ip, 0);
/*
--
1.9.0
_______________________________________________
xfs mailing list
xfs@xxxxxxxxxxx
http://oss.sgi.com/mailman/listinfo/xfs
