xfs: use WRITE_ONCE to update if_seq

This adds ordering of the updates and makes sure we always see the if_seq
update before the extent tree is modified.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 235b4ddcd324..49f5f5896a43 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -351,7 +351,7 @@ xfs_map_blocks(
         if (imap_valid &&
             (!xfs_inode_has_cow_data(ip) ||
              wpc->io_type == XFS_IO_COW ||
-             wpc->cow_seq == ip->i_cowfp->if_seq))
+             wpc->cow_seq == READ_ONCE(ip->i_cowfp->if_seq)))
                 return 0;
 
         if (XFS_FORCED_SHUTDOWN(mp))
@@ -380,7 +380,7 @@ xfs_map_blocks(
             xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &imap))
                 cow_fsb = imap.br_startoff;
         if (cow_fsb != NULLFILEOFF && cow_fsb <= offset_fsb) {
-                wpc->cow_seq = ip->i_cowfp->if_seq;
+                wpc->cow_seq = READ_ONCE(ip->i_cowfp->if_seq);
                 xfs_iunlock(ip, XFS_ILOCK_SHARED);
                 /*
                  * Truncate can race with writeback since writeback doesn't