On 07/03/2021 09:49, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: a38fd874 Linux 5.12-rc2 > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=143ee02ad00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=db9c6adb4986f2f2 > dashboard link: https://syzkaller.appspot.com/bug?extid=ac39856cb1b332dbbdda > > 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+ac39856cb1b332dbbdda@xxxxxxxxxxxxxxxxxxxxxxxxx Legit error, park() might take an sqd lock, and then we take it again. I'll patch it up > > ============================================ > WARNING: possible recursive locking detected > 5.12.0-rc2-syzkaller #0 Not tainted > -------------------------------------------- > kworker/u4:7/7615 is trying to acquire lock: > ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_stop fs/io_uring.c:7099 [inline] > ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_put_sq_data fs/io_uring.c:7115 [inline] > ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_finish+0x408/0x650 fs/io_uring.c:7139 > > but task is already holding lock: > ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7088 [inline] > ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park+0x63/0xc0 fs/io_uring.c:7082 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(&sqd->lock); > lock(&sqd->lock); > > *** DEADLOCK *** > > May be due to missing lock nesting notation > > 3 locks held by kworker/u4:7/7615: > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline] > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline] > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline] > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline] > #0: ffff888010469138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x871/0x1600 kernel/workqueue.c:2246 > #1: ffffc900023a7da8 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1600 kernel/workqueue.c:2250 > #2: ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7088 [inline] > #2: ffff888144a02870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park+0x63/0xc0 fs/io_uring.c:7082 > > stack backtrace: > CPU: 1 PID: 7615 Comm: kworker/u4:7 Not tainted 5.12.0-rc2-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Workqueue: events_unbound io_ring_exit_work > Call Trace: > __dump_stack lib/dump_stack.c:79 [inline] > dump_stack+0x141/0x1d7 lib/dump_stack.c:120 > print_deadlock_bug kernel/locking/lockdep.c:2829 [inline] > check_deadlock kernel/locking/lockdep.c:2872 [inline] > validate_chain kernel/locking/lockdep.c:3661 [inline] > __lock_acquire.cold+0x14c/0x3b4 kernel/locking/lockdep.c:4900 > lock_acquire kernel/locking/lockdep.c:5510 [inline] > lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5475 > __mutex_lock_common kernel/locking/mutex.c:946 [inline] > __mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1093 > io_sq_thread_stop fs/io_uring.c:7099 [inline] > io_put_sq_data fs/io_uring.c:7115 [inline] > io_sq_thread_finish+0x408/0x650 fs/io_uring.c:7139 > io_ring_ctx_free fs/io_uring.c:8408 [inline] > io_ring_exit_work+0x82/0x9a0 fs/io_uring.c:8539 > process_one_work+0x98d/0x1600 kernel/workqueue.c:2275 > worker_thread+0x64c/0x1120 kernel/workqueue.c:2421 > kthread+0x3b1/0x4a0 kernel/kthread.c:292 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294 > > > --- > 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > -- Pavel Begunkov
