xfs: handle racy AIO in xfs_reflink_end_cow

BugLink: http://bugs.launchpad.net/bugs/1731951
commit e12199f85d0ad1b04ce6c425ad93cd847fe930bb upstream.

If we got two AIO writes into a COW area the second one might not have any
COW extents left to convert.  Handle that case gracefully instead of
triggering an assert or accessing beyond the bounds of the extent list.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index f45fbf0db9bbea2cfb9578afd76de61b44bc7285..8c8390a7f121e295a5dc730514c18fab55b73028 100644 (file)
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -735,7 +735,13 @@ xfs_reflink_end_cow(
        /* If there is a hole at end_fsb - 1 go to the previous extent */
        if (!xfs_iext_lookup_extent(ip, ifp, end_fsb - 1, &idx, &got) ||
            got.br_startoff > end_fsb) {
-               ASSERT(idx > 0);
+               /*
+                * In case of racing, overlapping AIO writes no COW extents
+                * might be left by the time I/O completes for the loser of
+                * the race.  In that case we are done.
+                */
+               if (idx <= 0)
+                       goto out_cancel;
                xfs_iext_get_extent(ifp, --idx, &got);
        }
 
@@ -807,6 +813,7 @@ next_extent:
 
 out_defer:
        xfs_defer_cancel(&dfops);
+out_cancel:
        xfs_trans_cancel(tp);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
 out: