From: Qu Wenruo wqu@suse.com
[ Upstream commit d61acbbf54c612ea9bf67eed609494cda0857b3a ]
[BUG] There are some reports about btrfs wait forever to unmount itself, with the following call trace:
INFO: task umount:4631 blocked for more than 491 seconds. Tainted: G X 5.3.8-2-default #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. umount D 0 4631 3337 0x00000000 Call Trace: ([<00000000174adf7a>] __schedule+0x342/0x748) [<00000000174ae3ca>] schedule+0x4a/0xd8 [<00000000174b1f08>] schedule_timeout+0x218/0x420 [<00000000174af10c>] wait_for_common+0x104/0x1d8 [<000003ff804d6994>] btrfs_qgroup_wait_for_completion+0x84/0xb0 [btrfs] [<000003ff8044a616>] close_ctree+0x4e/0x380 [btrfs] [<0000000016fa3136>] generic_shutdown_super+0x8e/0x158 [<0000000016fa34d6>] kill_anon_super+0x26/0x40 [<000003ff8041ba88>] btrfs_kill_super+0x28/0xc8 [btrfs] [<0000000016fa39f8>] deactivate_locked_super+0x68/0x98 [<0000000016fcb198>] cleanup_mnt+0xc0/0x140 [<0000000016d6a846>] task_work_run+0xc6/0x110 [<0000000016d04f76>] do_notify_resume+0xae/0xb8 [<00000000174b30ae>] system_call+0xe2/0x2c8
[CAUSE] The problem happens when we have called qgroup_rescan_init(), but not queued the worker. It can be caused mostly by error handling.
Qgroup ioctl thread | Unmount thread ----------------------------------------+----------------------------------- | btrfs_qgroup_rescan() | |- qgroup_rescan_init() | | |- qgroup_rescan_running = true; | | | |- trans = btrfs_join_transaction() | | Some error happened | | | |- btrfs_qgroup_rescan() returns error | But qgroup_rescan_running == true; | | close_ctree() | |- btrfs_qgroup_wait_for_completion() | |- running == true; | |- wait_for_completion();
btrfs_qgroup_rescan_worker is never queued, thus no one is going to wake up close_ctree() and we get a deadlock.
All involved qgroup_rescan_init() callers are:
- btrfs_qgroup_rescan() The example above. It's possible to trigger the deadlock when error happened.
- btrfs_quota_enable() Not possible. Just after qgroup_rescan_init() we queue the work.
- btrfs_read_qgroup_config() It's possible to trigger the deadlock. It only init the work, the work queueing happens in btrfs_qgroup_rescan_resume(). Thus if error happened in between, deadlock is possible.
We shouldn't set fs_info->qgroup_rescan_running just in qgroup_rescan_init(), as at that stage we haven't yet queued qgroup rescan worker to run.
[FIX] Set qgroup_rescan_running before queueing the work, so that we ensure the rescan work is queued when we wait for it.
Fixes: 8d9eddad1946 ("Btrfs: fix qgroup rescan worker initialization") Signed-off-by: Jeff Mahoney jeffm@suse.com [ Change subject and cause analyse, use a smaller fix ] Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/qgroup.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index 410b791f28a56..06d4c219742f2 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1030,6 +1030,7 @@ out_add_root: ret = qgroup_rescan_init(fs_info, 0, 1); if (!ret) { qgroup_rescan_zero_tracking(fs_info); + fs_info->qgroup_rescan_running = true; btrfs_queue_work(fs_info->qgroup_rescan_workers, &fs_info->qgroup_rescan_work); } @@ -3276,7 +3277,6 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid, sizeof(fs_info->qgroup_rescan_progress)); fs_info->qgroup_rescan_progress.objectid = progress_objectid; init_completion(&fs_info->qgroup_rescan_completion); - fs_info->qgroup_rescan_running = true;
spin_unlock(&fs_info->qgroup_lock); mutex_unlock(&fs_info->qgroup_rescan_lock); @@ -3339,8 +3339,11 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
qgroup_rescan_zero_tracking(fs_info);
+ mutex_lock(&fs_info->qgroup_rescan_lock); + fs_info->qgroup_rescan_running = true; btrfs_queue_work(fs_info->qgroup_rescan_workers, &fs_info->qgroup_rescan_work); + mutex_unlock(&fs_info->qgroup_rescan_lock);
return 0; } @@ -3376,9 +3379,13 @@ int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info, void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info) { - if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) + if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) { + mutex_lock(&fs_info->qgroup_rescan_lock); + fs_info->qgroup_rescan_running = true; btrfs_queue_work(fs_info->qgroup_rescan_workers, &fs_info->qgroup_rescan_work); + mutex_unlock(&fs_info->qgroup_rescan_lock); + } }
/*