[XFS] In actual allocation of file system blocks and freeing extents, the

transaction within each such operation may involve multiple locking of AGF
buffer. While the freeing extent function has sorted the extents based on
AGF number before entering into transaction, however, when the file system
space is very limited, the allocation of space would try every AGF to get
space allocated, this could potentially cause out-of-order locking, thus
deadlock could happen. This fix mitigates the scarce space for allocation
by setting aside a few blocks without reservation, and avoid deadlock by
maintaining ascending order of AGF locking.

SGI-PV: 947395
SGI-Modid: xfs-linux-melb:xfs-kern:210801a

Signed-off-by: Yingping Lu <yingping@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/fs/xfs/xfs_bmap_btree.c b/fs/xfs/xfs_bmap_btree.c
index bea44709afb..3b6dfc9b53a 100644
--- a/fs/xfs/xfs_bmap_btree.c
+++ b/fs/xfs/xfs_bmap_btree.c
@@ -1569,12 +1569,11 @@ xfs_bmbt_split(
         lbno = XFS_DADDR_TO_FSB(args.mp, XFS_BUF_ADDR(lbp));
         left = XFS_BUF_TO_BMBT_BLOCK(lbp);
         args.fsbno = cur->bc_private.b.firstblock;
+        args.firstblock = args.fsbno;
         if (args.fsbno == NULLFSBLOCK) {
                 args.fsbno = lbno;
                 args.type = XFS_ALLOCTYPE_START_BNO;
-        } else if (cur->bc_private.b.flist->xbf_low)
-                args.type = XFS_ALLOCTYPE_FIRST_AG;
-        else
+        } else
                 args.type = XFS_ALLOCTYPE_NEAR_BNO;
         args.mod = args.minleft = args.alignment = args.total = args.isfl =
                 args.userdata = args.minalignslop = 0;
@@ -2356,6 +2355,7 @@ xfs_bmbt_newroot(
                 args.userdata = args.minalignslop = 0;
         args.minlen = args.maxlen = args.prod = 1;
         args.wasdel = cur->bc_private.b.flags & XFS_BTCUR_BPRV_WASDEL;
+        args.firstblock = args.fsbno;
         if (args.fsbno == NULLFSBLOCK) {
 #ifdef DEBUG
                 if ((error = xfs_btree_check_lptr(cur, INT_GET(*pp, ARCH_CONVERT), level))) {
@@ -2365,9 +2365,7 @@ xfs_bmbt_newroot(
 #endif
                 args.fsbno = INT_GET(*pp, ARCH_CONVERT);
                 args.type = XFS_ALLOCTYPE_START_BNO;
-        } else if (args.wasdel)
-                args.type = XFS_ALLOCTYPE_FIRST_AG;
-        else
+        } else
                 args.type = XFS_ALLOCTYPE_NEAR_BNO;
         if ((error = xfs_alloc_vextent(&args))) {
                 XFS_BMBT_TRACE_CURSOR(cur, ERROR);