[Ocfs2-devel] [Ocfs2-dev] BUG: deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread

[Shichangkuo]

Hi all,
　　Now we are testing ocfs2 with 4.14 kernel, and we finding a deadlock with umount and ocfs2 workqueue triggered by ocfs2rec thread. The stack as follows:
journal recovery work:
[<ffffffff8a8c0694>] call_rwsem_down_read_failed+0x14/0x30
[<ffffffffc0d5d652>] ocfs2_finish_quota_recovery+0x62/0x450 [ocfs2]
[<ffffffffc0d21221>] ocfs2_complete_recovery+0xc1/0x440 [ocfs2]
[<ffffffff8a09a1f0>] process_one_work+0x130/0x350
[<ffffffff8a09a946>] worker_thread+0x46/0x3b0
[<ffffffff8a0a0e51>] kthread+0x101/0x140
[<ffffffff8aa002ff>] ret_from_fork+0x1f/0x30
[<ffffffffffffffff>] 0xffffffffffffffff

/bin/umount:
[<ffffffff8a099b24>] flush_workqueue+0x104/0x3e0
[<ffffffffc0cf18db>] ocfs2_truncate_log_shutdown+0x3b/0xc0 [ocfs2]
[<ffffffffc0d4fd6c>] ocfs2_dismount_volume+0x8c/0x3d0 [ocfs2]
[<ffffffffc0d500e1>] ocfs2_put_super+0x31/0xa0 [ocfs2]
[<ffffffff8a2445bd>] generic_shutdown_super+0x6d/0x120
[<ffffffff8a24469d>] kill_block_super+0x2d/0x60
[<ffffffff8a244e71>] deactivate_locked_super+0x51/0x90
[<ffffffff8a263a1b>] cleanup_mnt+0x3b/0x70
[<ffffffff8a09e9c6>] task_work_run+0x86/0xa0
[<ffffffff8a003d70>] exit_to_usermode_loop+0x6d/0xa9
[<ffffffff8a003a2d>] do_syscall_64+0x11d/0x130
[<ffffffff8aa00113>] entry_SYSCALL64_slow_path+0x25/0x25
[<ffffffffffffffff>] 0xffffffffffffffff
　　
Function ocfs2_finish_quota_recovery try to get sb->s_umount, which was already locked by umount thread, then get a deadlock.
This issue was introduced by c3b004460d77bf3f980d877be539016f2df4df12 and 5f530de63cfc6ca8571cbdf58af63fb166cc6517.
I think we cannot use :: s_umount, but the mutex ::dqonoff_mutex was already removed.
Shall we add a new mutex?

Thanks
Changkuo
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