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 <[email protected]> Reported-by: Nikolay Borisov <[email protected]> Reviewed-by: Darrick J. Wong <[email protected]> Signed-off-by: Darrick J. Wong <[email protected]>
IreneKnapp · Jul 26, 2017 · 5b094d6 · 5b094d6
1 parent 6215894
commit 5b094d6
Showing 1 changed file with 12 additions and 0 deletions.
diff --git 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;