xfs: set firstfsb to NULLFSBLOCK before feeding it to _bmapi_write

Source kernel commit: 4c1a67bd3606540b9b42caff34a1d5cd94b1cf65

We must initialize the firstfsb parameter to _bmapi_write so that it
doesn't incorrectly treat stack garbage as a restriction on which AGs
it can search for free space.

Fixes-coverity-id: 1402025
Fixes-coverity-id: 1415167
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/libxfs/xfs_bmap.c b/libxfs/xfs_bmap.c
index d44a4e9e720d95a2409f4c8e14e54e4cc3c8e5a3..d11e4d6567cdee4cdb018acafb4f0d11c7db435a 100644 (file)
--- a/libxfs/xfs_bmap.c
+++ b/libxfs/xfs_bmap.c
@@ -6490,6 +6490,15 @@ xfs_bmap_finish_one(
        xfs_fsblock_t                   firstfsb;
        int                             error = 0;
 
+       /*
+        * firstfsb is tied to the transaction lifetime and is used to
+        * ensure correct AG locking order and schedule work item
+        * continuations.  XFS_BUI_MAX_FAST_EXTENTS (== 1) restricts us
+        * to only making one bmap call per transaction, so it should
+        * be safe to have it as a local variable here.
+        */
+       firstfsb = NULLFSBLOCK;
+
        trace_xfs_bmap_deferred(tp->t_mountp,
                        XFS_FSB_TO_AGNO(tp->t_mountp, startblock), type,
                        XFS_FSB_TO_AGBNO(tp->t_mountp, startblock),