diff options
| -rw-r--r-- | fs/xfs/libxfs/xfs_btree.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c index 35f574421670..da8c769887fd 100644 --- a/fs/xfs/libxfs/xfs_btree.c +++ b/fs/xfs/libxfs/xfs_btree.c @@ -2913,9 +2913,22 @@ xfs_btree_split_worker( } /* - * BMBT split requests often come in with little stack to work on. Push + * BMBT split requests often come in with little stack to work on so we push * them off to a worker thread so there is lots of stack to use. For the other * btree types, just call directly to avoid the context switch overhead here. + * + * Care must be taken here - the work queue rescuer thread introduces potential + * AGF <> worker queue deadlocks if the BMBT block allocation has to lock new + * AGFs to allocate blocks. A task being run by the rescuer could attempt to + * lock an AGF that is already locked by a task queued to run by the rescuer, + * resulting in an ABBA deadlock as the rescuer cannot run the lock holder to + * release it until the current thread it is running gains the lock. + * + * To avoid this issue, we only ever queue BMBT splits that don't have an AGF + * already locked to allocate from. The only place that doesn't hold an AGF + * locked is unwritten extent conversion at IO completion, but that has already + * been offloaded to a worker thread and hence has no stack consumption issues + * we have to worry about. */ STATIC int /* error */ xfs_btree_split( @@ -2929,7 +2942,8 @@ xfs_btree_split( struct xfs_btree_split_args args; DECLARE_COMPLETION_ONSTACK(done); - if (cur->bc_btnum != XFS_BTNUM_BMAP) + if (cur->bc_btnum != XFS_BTNUM_BMAP || + cur->bc_tp->t_firstblock == NULLFSBLOCK) return __xfs_btree_split(cur, level, ptrp, key, curp, stat); args.cur = cur; |