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Tue, 09 Mar 2021 06:04:17 -0800 (PST) Date: Tue, 09 Mar 2021 06:04:17 -0800 In-Reply-To: <000000000000430bf505bcef3b00@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <000000000000b71e9605bd1b064f@google.com> Subject: Re: [syzbot] possible deadlock in io_sq_thread_finish From: syzbot To: asml.silence@gmail.com, axboe@kernel.dk, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org syzbot has found a reproducer for the following issue on: HEAD commit: 144c79ef Merge tag 'perf-tools-fixes-for-v5.12-2020-03-07'.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=129addbcd00000 kernel config: https://syzkaller.appspot.com/x/.config?x=db9c6adb4986f2f2 dashboard link: https://syzkaller.appspot.com/bug?extid=ac39856cb1b332dbbdda syz repro: https://syzkaller.appspot.com/x/repro.syz?x=167574dad00000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12c8f566d00000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+ac39856cb1b332dbbdda@syzkaller.appspotmail.com ============================================ WARNING: possible recursive locking detected 5.12.0-rc2-syzkaller #0 Not tainted -------------------------------------------- kworker/u4:7/8696 is trying to acquire lock: ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_stop fs/io_uring.c:7099 [inline] ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_put_sq_data fs/io_uring.c:7115 [inline] ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_finish+0x408/0x650 fs/io_uring.c:7139 but task is already holding lock: ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7088 [inline] ffff888015395870 (&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/u4:7/8696: #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: ffffc9000253fda8 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1600 kernel/workqueue.c:2250 #2: ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park fs/io_uring.c:7088 [inline] #2: ffff888015395870 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park+0x63/0xc0 fs/io_uring.c:7082 stack backtrace: CPU: 0 PID: 8696 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