syzbot


possible deadlock in refcount_dec_and_mutex_lock

Status: auto-closed as invalid on 2019/11/20 04:39
Reported-by: syzbot+22987eb604bffbcb717a@syzkaller.appspotmail.com
First crash: 1013d, last: 1013d
similar bugs (2):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 possible deadlock in refcount_dec_and_mutex_lock C done done 5 914d 970d 1/1 fixed on 2020/01/28 16:29
linux-4.14 possible deadlock in refcount_dec_and_mutex_lock C done 10 917d 990d 1/1 fixed on 2020/01/25 22:00

Sample crash report:
block nbd3: Receive control failed (result -22)
======================================================
WARNING: possible circular locking dependency detected
5.3.0-next-20190920 #0 Not tainted
------------------------------------------------------
kworker/u5:0/1524 is trying to acquire lock:
ffff8880a3030978 (&nbd->config_lock){+.+.}, at: refcount_dec_and_mutex_lock lib/refcount.c:319 [inline]
ffff8880a3030978 (&nbd->config_lock){+.+.}, at: refcount_dec_and_mutex_lock+0x56/0x90 lib/refcount.c:314

but task is already holding lock:
ffff8880a63ffdc0 ((work_completion)(&args->work)){+.+.}, at: process_one_work+0x8c1/0x1740 kernel/workqueue.c:2244

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((work_completion)(&args->work)){+.+.}:
       process_one_work+0x91c/0x1740 kernel/workqueue.c:2245
       worker_thread+0x98/0xe40 kernel/workqueue.c:2415
       kthread+0x361/0x430 kernel/kthread.c:255
       ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

-> #1 ((wq_completion)knbd0-recv){+.+.}:
       flush_workqueue+0x126/0x14c0 kernel/workqueue.c:2774
       drain_workqueue+0x1b4/0x470 kernel/workqueue.c:2939
       destroy_workqueue+0x74/0x750 kernel/workqueue.c:4335
       nbd_config_put+0x3dd/0x870 drivers/block/nbd.c:1181
       nbd_release+0x103/0x150 drivers/block/nbd.c:1460
       __blkdev_put+0x4d1/0x810 fs/block_dev.c:1867
       blkdev_put+0x98/0x560 fs/block_dev.c:1929
       blkdev_close+0x8b/0xb0 fs/block_dev.c:1936
       __fput+0x2ff/0x890 fs/file_table.c:280
       ____fput+0x16/0x20 fs/file_table.c:313
       task_work_run+0x145/0x1c0 kernel/task_work.c:113
       exit_task_work include/linux/task_work.h:22 [inline]
       do_exit+0x904/0x2e60 kernel/exit.c:879
       do_group_exit+0x135/0x360 kernel/exit.c:983
       __do_sys_exit_group kernel/exit.c:994 [inline]
       __se_sys_exit_group kernel/exit.c:992 [inline]
       __x64_sys_exit_group+0x44/0x50 kernel/exit.c:992
       do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&nbd->config_lock){+.+.}:
       check_prev_add kernel/locking/lockdep.c:2476 [inline]
       check_prevs_add kernel/locking/lockdep.c:2581 [inline]
       validate_chain kernel/locking/lockdep.c:2971 [inline]
       __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955
       lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
       refcount_dec_and_mutex_lock lib/refcount.c:319 [inline]
       refcount_dec_and_mutex_lock+0x56/0x90 lib/refcount.c:314
       nbd_config_put+0x31/0x870 drivers/block/nbd.c:1159
       recv_work+0x19b/0x200 drivers/block/nbd.c:787
       process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
       worker_thread+0x98/0xe40 kernel/workqueue.c:2415
       kthread+0x361/0x430 kernel/kthread.c:255
       ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

other info that might help us debug this:

Chain exists of:
  &nbd->config_lock --> (wq_completion)knbd0-recv --> (work_completion)(&args->work)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&args->work));
                               lock((wq_completion)knbd0-recv);
                               lock((work_completion)(&args->work));
  lock(&nbd->config_lock);

 *** DEADLOCK ***

2 locks held by kworker/u5:0/1524:
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: __write_once_size include/linux/compiler.h:226 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:855 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:40 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: set_work_data kernel/workqueue.c:620 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline]
 #0: ffff8880948d3d28 ((wq_completion)knbd3-recv){+.+.}, at: process_one_work+0x88b/0x1740 kernel/workqueue.c:2240
 #1: ffff8880a63ffdc0 ((work_completion)(&args->work)){+.+.}, at: process_one_work+0x8c1/0x1740 kernel/workqueue.c:2244

stack backtrace:
CPU: 1 PID: 1524 Comm: kworker/u5:0 Not tainted 5.3.0-next-20190920 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: knbd3-recv recv_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1685
 check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1809
 check_prev_add kernel/locking/lockdep.c:2476 [inline]
 check_prevs_add kernel/locking/lockdep.c:2581 [inline]
 validate_chain kernel/locking/lockdep.c:2971 [inline]
 __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3955
 lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
 __mutex_lock_common kernel/locking/mutex.c:956 [inline]
 __mutex_lock+0x156/0x13c0 kernel/locking/mutex.c:1103
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
 refcount_dec_and_mutex_lock lib/refcount.c:319 [inline]
 refcount_dec_and_mutex_lock+0x56/0x90 lib/refcount.c:314
 nbd_config_put+0x31/0x870 drivers/block/nbd.c:1159
 recv_work+0x19b/0x200 drivers/block/nbd.c:787
 process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x361/0x430 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
block nbd3: shutting down sockets

Crashes (1):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-linux-next-kasan-gce-root 2019/09/21 04:38 linux-next b5b3bd898ba9 d96e88f3 .config log report