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Date:   Sun, 22 Nov 2020 13:15:15 -0800
From:   syzbot <syzbot+f60646ed0fee22ac695d@...kaller.appspotmail.com>
To:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: possible deadlock in freeze_super

Hello,

syzbot found the following issue on:

HEAD commit:    a349e4c6 Merge tag 'xfs-5.10-fixes-7' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16158d71500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6867674f76eceeb6
dashboard link: https://syzkaller.appspot.com/bug?extid=f60646ed0fee22ac695d
compiler:       gcc (GCC) 10.1.0-syz 20200507

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f60646ed0fee22ac695d@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.10.0-rc4-syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:1H/2986 is trying to acquire lock:
ffff88801cdca0e0 (&type->s_umount_key#83){+.+.}-{3:3}, at: freeze_super+0x41/0x330 fs/super.c:1716

but task is already holding lock:
ffffc90001b2fda8 ((work_completion)(&(&gl->gl_work)->work)){+.+.}-{0:0}, at: process_one_work+0x854/0x15a0 kernel/workqueue.c:2247

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((work_completion)(&(&gl->gl_work)->work)){+.+.}-{0:0}:
       process_one_work+0x8a2/0x15a0 kernel/workqueue.c:2248
       worker_thread+0x64c/0x1120 kernel/workqueue.c:2418
       kthread+0x3af/0x4a0 kernel/kthread.c:292
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

-> #1 ((wq_completion)glock_workqueue){+.+.}-{0:0}:
       flush_workqueue+0x110/0x13e0 kernel/workqueue.c:2783
       gfs2_gl_hash_clear+0xad/0x270 fs/gfs2/glock.c:1987
       gfs2_put_super+0x44b/0x680 fs/gfs2/super.c:740
       generic_shutdown_super+0x144/0x370 fs/super.c:464
       kill_block_super+0x97/0xf0 fs/super.c:1446
       gfs2_kill_sb+0x104/0x160 fs/gfs2/ops_fstype.c:1662
       deactivate_locked_super+0x94/0x160 fs/super.c:335
       deactivate_super+0xad/0xd0 fs/super.c:366
       cleanup_mnt+0x3a3/0x530 fs/namespace.c:1118
       task_work_run+0xdd/0x190 kernel/task_work.c:151
       tracehook_notify_resume include/linux/tracehook.h:188 [inline]
       exit_to_user_mode_loop kernel/entry/common.c:164 [inline]
       exit_to_user_mode_prepare+0x17e/0x1a0 kernel/entry/common.c:191
       syscall_exit_to_user_mode+0x38/0x260 kernel/entry/common.c:266
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #0 (&type->s_umount_key#83){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2866 [inline]
       check_prevs_add kernel/locking/lockdep.c:2991 [inline]
       validate_chain kernel/locking/lockdep.c:3606 [inline]
       __lock_acquire+0x2ca6/0x5c00 kernel/locking/lockdep.c:4830
       lock_acquire kernel/locking/lockdep.c:5435 [inline]
       lock_acquire+0x2a3/0x8c0 kernel/locking/lockdep.c:5400
       down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
       freeze_super+0x41/0x330 fs/super.c:1716
       freeze_go_sync+0x193/0x2c0 fs/gfs2/glops.c:587
       do_xmote+0x2ff/0xbc0 fs/gfs2/glock.c:616
       run_queue+0x323/0x680 fs/gfs2/glock.c:753
       glock_work_func+0xff/0x3f0 fs/gfs2/glock.c:926
       process_one_work+0x933/0x15a0 kernel/workqueue.c:2272
       worker_thread+0x64c/0x1120 kernel/workqueue.c:2418
       kthread+0x3af/0x4a0 kernel/kthread.c:292
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

other info that might help us debug this:

Chain exists of:
  &type->s_umount_key#83 --> (wq_completion)glock_workqueue --> (work_completion)(&(&gl->gl_work)->work)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&(&gl->gl_work)->work));
                               lock((wq_completion)glock_workqueue);
                               lock((work_completion)(&(&gl->gl_work)->work));
  lock(&type->s_umount_key#83);

 *** DEADLOCK ***

2 locks held by kworker/0:1H/2986:
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff888016d03938 ((wq_completion)glock_workqueue){+.+.}-{0:0}, at: process_one_work+0x821/0x15a0 kernel/workqueue.c:2243
 #1: ffffc90001b2fda8 ((work_completion)(&(&gl->gl_work)->work)){+.+.}-{0:0}, at: process_one_work+0x854/0x15a0 kernel/workqueue.c:2247

stack backtrace:
CPU: 0 PID: 2986 Comm: kworker/0:1H Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: glock_workqueue glock_work_func
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2115
 check_prev_add kernel/locking/lockdep.c:2866 [inline]
 check_prevs_add kernel/locking/lockdep.c:2991 [inline]
 validate_chain kernel/locking/lockdep.c:3606 [inline]
 __lock_acquire+0x2ca6/0x5c00 kernel/locking/lockdep.c:4830
 lock_acquire kernel/locking/lockdep.c:5435 [inline]
 lock_acquire+0x2a3/0x8c0 kernel/locking/lockdep.c:5400
 down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
 freeze_super+0x41/0x330 fs/super.c:1716
 freeze_go_sync+0x193/0x2c0 fs/gfs2/glops.c:587
 do_xmote+0x2ff/0xbc0 fs/gfs2/glock.c:616
 run_queue+0x323/0x680 fs/gfs2/glock.c:753
 glock_work_func+0xff/0x3f0 fs/gfs2/glock.c:926
 process_one_work+0x933/0x15a0 kernel/workqueue.c:2272
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2418
 kthread+0x3af/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@...glegroups.com.

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