On 7/15/21 10:15 AM, syzbot wrote: > Hello, > > syzbot has tested the proposed patch but the reproducer is still triggering an issue: > INFO: task hung in io_sq_thread_park The interesting part here is this: [ 282.599913][ T1620] task:iou-sqp-23145 state:D stack:28720 pid:23155 ppid: 8844 flags:0x00004004 [ 282.609927][ T1620] Call Trace: [ 282.613711][ T1620] __schedule+0x93a/0x26f0 [ 282.618131][ T1620] ? io_schedule_timeout+0x140/0x140 [ 282.623446][ T1620] ? lockdep_hardirqs_on+0x79/0x100 [ 282.628789][ T1620] ? _raw_spin_unlock_irqrestore+0x3d/0x70 [ 282.634647][ T1620] schedule+0xd3/0x270 [ 282.638874][ T1620] io_uring_cancel_generic+0x54d/0x890 [ 282.644428][ T1620] ? __io_uring_free+0x170/0x170 [ 282.649361][ T1620] ? lockdep_hardirqs_on+0x79/0x100 [ 282.655639][ T1620] ? finish_wait+0x270/0x270 [ 282.660346][ T1620] io_sq_thread+0xaac/0x1250 [ 282.665096][ T1620] ? io_uring_cancel_generic+0x890/0x890 [ 282.670788][ T1620] ? ret_from_fork+0x8/0x30 [ 282.675295][ T1620] ? finish_wait+0x270/0x270 [ 282.679983][ T1620] ? rwlock_bug.part.0+0x90/0x90 [ 282.684958][ T1620] ? _raw_spin_unlock_irq+0x1f/0x40 [ 282.690155][ T1620] ? io_uring_cancel_generic+0x890/0x890 [ 282.696394][ T1620] ret_from_fork+0x1f/0x30 So we have a dying SQPOLL task, which is stuck in cancellation. Let's add some debug output and see if we have a request lost. #syz test: https://github.com/isilence/linux.git syztest_sqpoll_hang > INFO: task kworker/u4:1:10 blocked for more than 143 seconds. > Not tainted 5.14.0-rc1-syzkaller #0 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/u4:1 state:D stack:26320 pid: 10 ppid: 2 flags:0x00004000 > Workqueue: events_unbound io_ring_exit_work > Call Trace: > context_switch kernel/sched/core.c:4683 [inline] > __schedule+0x93a/0x26f0 kernel/sched/core.c:5940 > schedule+0xd3/0x270 kernel/sched/core.c:6019 > schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6078 > __mutex_lock_common kernel/locking/mutex.c:1036 [inline] > __mutex_lock+0x7b6/0x10a0 kernel/locking/mutex.c:1104 > io_sq_thread_park+0x79/0xd0 fs/io_uring.c:7314 > io_ring_exit_work+0x15a/0x1600 fs/io_uring.c:8771 > process_one_work+0x98d/0x1630 kernel/workqueue.c:2276 > worker_thread+0x658/0x11f0 kernel/workqueue.c:2422 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > INFO: task iou-sqp-23145:23155 blocked for more than 143 seconds. > Not tainted 5.14.0-rc1-syzkaller #0 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:iou-sqp-23145 state:D stack:28720 pid:23155 ppid: 8844 flags:0x00004004 > Call Trace: > context_switch kernel/sched/core.c:4683 [inline] > __schedule+0x93a/0x26f0 kernel/sched/core.c:5940 > schedule+0xd3/0x270 kernel/sched/core.c:6019 > io_uring_cancel_generic+0x54d/0x890 fs/io_uring.c:9150 > io_sq_thread+0xaac/0x1250 fs/io_uring.c:6916 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > Showing all locks held in the system: > 3 locks held by kworker/u4:1/10: > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:620 [inline] > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline] > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:617 [inline] > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline] > #0: ffff888010869138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x871/0x1630 kernel/workqueue.c:2247 > #1: ffffc90000cf7db0 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1630 kernel/workqueue.c:2251 > #2: ffff88803d708470 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread_park+0x79/0xd0 fs/io_uring.c:7314 > 1 lock held by khungtaskd/1620: > #0: ffffffff8b97b900 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6446 > 1 lock held by in:imklog/8316: > #0: ffff888022f82ff0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:974 > 1 lock held by iou-sqp-23145/23155: > #0: ffff88803d708470 (&sqd->lock){+.+.}-{3:3}, at: io_sqd_handle_event+0x2d6/0x350 fs/io_uring.c:6836 > > ============================================= > > NMI backtrace for cpu 1 > CPU: 1 PID: 1620 Comm: khungtaskd Not tainted 5.14.0-rc1-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105 > nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105 > nmi_trigger_cpumask_backtrace+0x1b3/0x230 lib/nmi_backtrace.c:62 > trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline] > check_hung_uninterruptible_tasks kernel/hung_task.c:210 [inline] > watchdog+0xd0a/0xfc0 kernel/hung_task.c:295 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > Sending NMI from CPU 1 to CPUs 0: > NMI backtrace for cpu 0 > CPU: 0 PID: 10540 Comm: kworker/u4:10 Not tainted 5.14.0-rc1-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Workqueue: phy8 ieee80211_iface_work > RIP: 0010:write_comp_data kernel/kcov.c:218 [inline] > RIP: 0010:__sanitizer_cov_trace_switch+0x65/0xf0 kernel/kcov.c:320 > Code: 10 31 c9 65 4c 8b 24 25 00 f0 01 00 4d 85 d2 74 6b 4c 89 e6 bf 03 00 00 00 4c 8b 4c 24 20 49 8b 6c c8 10 e8 2d ff ff ff 84 c0 <74> 47 49 8b 84 24 18 15 00 00 41 8b bc 24 14 15 00 00 48 8b 10 48 > RSP: 0018:ffffc9000bfa7030 EFLAGS: 00000246 > RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000016 > RDX: 0000000000000000 RSI: ffff88801c5d8000 RDI: 0000000000000003 > RBP: 0000000000000084 R08: ffffffff8aaa7a20 R09: ffffffff88878073 > R10: 0000000000000020 R11: 0000000000000003 R12: ffff88801c5d8000 > R13: dffffc0000000000 R14: ffff888053061087 R15: ffff888053061086 > FS: 0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f87cdfe4090 CR3: 000000002a61f000 CR4: 0000000000350ef0 > Call Trace: > _ieee802_11_parse_elems_crc+0x1e3/0x1f90 net/mac80211/util.c:1018 > ieee802_11_parse_elems_crc+0x89e/0xfe0 net/mac80211/util.c:1478 > ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2186 [inline] > ieee80211_bss_info_update+0x463/0xb70 net/mac80211/scan.c:212 > ieee80211_rx_bss_info net/mac80211/ibss.c:1126 [inline] > ieee80211_rx_mgmt_probe_beacon+0xcc6/0x17c0 net/mac80211/ibss.c:1615 > ieee80211_ibss_rx_queued_mgmt+0xd30/0x1610 net/mac80211/ibss.c:1642 > ieee80211_iface_process_skb net/mac80211/iface.c:1426 [inline] > ieee80211_iface_work+0x7f7/0xa40 net/mac80211/iface.c:1462 > process_one_work+0x98d/0x1630 kernel/workqueue.c:2276 > worker_thread+0x658/0x11f0 kernel/workqueue.c:2422 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > > Tested on: > > commit: 1b48773f io_uring: fix io_drain_req() > git tree: git://git.kernel.dk/linux-block io_uring-5.14 > console output: https://syzkaller.appspot.com/x/log.txt?x=12040824300000 > kernel config: https://syzkaller.appspot.com/x/.config?x=cfe2c0e42bc9993d > dashboard link: https://syzkaller.appspot.com/bug?extid=ac957324022b7132accf > compiler: > -- Pavel Begunkov
