xfs: fix multi-AG deadlock in xfs_bunmapi

commit 5b094d6dac0451ad89b1dc088395c7b399b7e9e8 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 73571fb..2ab50ca 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5556,6 +5556,7 @@ __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_);
 
@@ -5658,6 +5659,17 @@ __xfs_bunmapi(
                ASSERT(ep != NULL);
                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;