xfs: fix multi-AG deadlock in xfs_bunmapi

Just like in the allocator we must avoid touching multiple AGs out of
order when freeing blocks, as freeing still locks the AGF and can cause
the same AB-BA deadlocks as in the allocation path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Nikolay Borisov <n.borisov.lkml@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index ee118ceb702fbefd0c34668cee28be587bb1c989..c09c16b1ad3b8b1f883e2ee93b9fcc275c7ed63c 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5435,6 +5435,7 @@ __xfs_bunmapi(
        xfs_fsblock_t           sum;
        xfs_filblks_t           len = *rlen;    /* length to unmap in file */
        xfs_fileoff_t           max_len;
+       xfs_agnumber_t          prev_agno = NULLAGNUMBER, agno;
 
        trace_xfs_bunmap(ip, bno, len, flags, _RET_IP_);
 
@@ -5534,6 +5535,17 @@ __xfs_bunmapi(
                 */
                del = got;
                wasdel = isnullstartblock(del.br_startblock);
+
+               /*
+                * Make sure we don't touch multiple AGF headers out of order
+                * in a single transaction, as that could cause AB-BA deadlocks.
+                */
+               if (!wasdel) {
+                       agno = XFS_FSB_TO_AGNO(mp, del.br_startblock);
+                       if (prev_agno != NULLAGNUMBER && prev_agno > agno)
+                               break;
+                       prev_agno = agno;
+               }
                if (got.br_startoff < start) {
                        del.br_startoff = start;
                        del.br_blockcount -= start - got.br_startoff;