Re: INFO: task can't die in io_sq_thread_stop

From: Xiaoguang Wang
Date: Mon Nov 16 2020 - 04:33:58 EST

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hi jens,

Hello,

syzbot found the following issue on:

HEAD commit: 6dd65e60 Add linux-next specific files for 20201110
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14727d42500000
kernel config: https://syzkaller.appspot.com/x/.config?x=4fab43daf5c54712
dashboard link: https://syzkaller.appspot.com/bug?extid=03beeb595f074db9cfd1
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+03beeb595f074db9cfd1@xxxxxxxxxxxxxxxxxxxxxxxxx

INFO: task syz-executor.2:12399 can't die for more than 143 seconds.
task:syz-executor.2 state:D stack:28744 pid:12399 ppid: 8504 flags:0x00004004
Call Trace:
context_switch kernel/sched/core.c:3773 [inline]
__schedule+0x893/0x2170 kernel/sched/core.c:4522
schedule+0xcf/0x270 kernel/sched/core.c:4600
schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1847
do_wait_for_common kernel/sched/completion.c:85 [inline]
__wait_for_common kernel/sched/completion.c:106 [inline]
wait_for_common kernel/sched/completion.c:117 [inline]
wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
kthread_stop+0x17a/0x720 kernel/kthread.c:596
io_put_sq_data fs/io_uring.c:7193 [inline]
io_sq_thread_stop+0x452/0x570 fs/io_uring.c:7290
io_finish_async fs/io_uring.c:7297 [inline]
io_sq_offload_create fs/io_uring.c:8015 [inline]
io_uring_create fs/io_uring.c:9433 [inline]
io_uring_setup+0x19b7/0x3730 fs/io_uring.c:9507
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

I also don't have a reproducer yet, but seems that there is a race
in current codes: |
=> io_put_sq_data |
==> kthread_park(sqd->thread); |
| T1: sq thread is parked now.
==> kthread_stop(sqd->thread); |
===> kthread_unpark(k); |
| T2: sq thread is now unpared, can run again
|
| T3: sq thread is now preempted out.
|
===> wake_up_process(k); |
|
| T4: Since sqd ctx list is empty, needs_sched will be true,
| then sq thread sets task state to TASK_INTERRUPTIBLE,
| and schedule, now sq thread will never be waken up.
===> wait_for_completion |

I have artificially used mdelay() to simulate above race, will get same stack like
this syzbot report.

- if (kthread_should_park())
+ if (kthread_should_park()) {
kthread_parkme();
+ if (kthread_should_stop())
+ break;
+ }
this diff can fix this issue, and if ctx_list is empty, we don't need to call schedule().

Regards,
Xiaoguang Wang

RIP: 0033:0x45deb9
Code: Unable to access opcode bytes at RIP 0x45de8f.
RSP: 002b:00007f174e51ac78 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9
RAX: ffffffffffffffda RBX: 0000000000008640 RCX: 000000000045deb9
RDX: 0000000000000000 RSI: 0000000020000140 RDI: 00000000000050e5
RBP: 000000000118bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007ffed9ca723f R14: 00007f174e51b9c0 R15: 000000000118bf2c
INFO: task syz-executor.2:12399 blocked for more than 143 seconds.
Not tainted 5.10.0-rc3-next-20201110-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2 state:D stack:28744 pid:12399 ppid: 8504 flags:0x00004004
Call Trace:
context_switch kernel/sched/core.c:3773 [inline]
__schedule+0x893/0x2170 kernel/sched/core.c:4522
schedule+0xcf/0x270 kernel/sched/core.c:4600
schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1847
do_wait_for_common kernel/sched/completion.c:85 [inline]
__wait_for_common kernel/sched/completion.c:106 [inline]
wait_for_common kernel/sched/completion.c:117 [inline]
wait_for_completion+0x163/0x260 kernel/sched/completion.c:138
kthread_stop+0x17a/0x720 kernel/kthread.c:596
io_put_sq_data fs/io_uring.c:7193 [inline]
io_sq_thread_stop+0x452/0x570 fs/io_uring.c:7290
io_finish_async fs/io_uring.c:7297 [inline]
io_sq_offload_create fs/io_uring.c:8015 [inline]
io_uring_create fs/io_uring.c:9433 [inline]
io_uring_setup+0x19b7/0x3730 fs/io_uring.c:9507
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45deb9
Code: Unable to access opcode bytes at RIP 0x45de8f.
RSP: 002b:00007f174e51ac78 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9
RAX: ffffffffffffffda RBX: 0000000000008640 RCX: 000000000045deb9
RDX: 0000000000000000 RSI: 0000000020000140 RDI: 00000000000050e5
RBP: 000000000118bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007ffed9ca723f R14: 00007f174e51b9c0 R15: 000000000118bf2c

Showing all locks held in the system:
1 lock held by khungtaskd/1653:
#0: ffffffff8b3386a0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6253
1 lock held by systemd-journal/4873:
1 lock held by in:imklog/8167:
#0: ffff88801c86e0f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:932

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 1653 Comm: khungtaskd Not tainted 5.10.0-rc3-next-20201110-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x107/0x163 lib/dump_stack.c:118
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:147 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:253 [inline]
watchdog+0xd89/0xf30 kernel/hung_task.c:338
kthread+0x3af/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.10.0-rc3-next-20201110-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events nsim_dev_trap_report_work
RIP: 0010:mark_lock+0x30/0x24c0 kernel/locking/lockdep.c:4371
Code: 41 54 41 89 d4 48 ba 00 00 00 00 00 fc ff df 55 53 48 81 ec 18 01 00 00 48 8d 5c 24 38 48 89 3c 24 48 c7 44 24 38 b3 8a b5 41 <48> c1 eb 03 48 c7 44 24 40 30 1b c6 8a 48 8d 04 13 48 c7 44 24 48
RSP: 0018:ffffc90000ca7988 EFLAGS: 00000096
RAX: 0000000000000004 RBX: ffffc90000ca79c0 RCX: ffffffff8155b947
RDX: dffffc0000000000 RSI: ffff888010d20918 RDI: ffff888010d20000
RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8ebb477f
R10: fffffbfff1d768ef R11: 000000004fb6aa4b R12: 0000000000000006
R13: dffffc0000000000 R14: ffff888010d20918 R15: 0000000000000022
FS: 0000000000000000(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8ffcf99000 CR3: 000000001b2e7000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
mark_held_locks+0x9f/0xe0 kernel/locking/lockdep.c:4011
__trace_hardirqs_on_caller kernel/locking/lockdep.c:4037 [inline]
lockdep_hardirqs_on_prepare kernel/locking/lockdep.c:4097 [inline]
lockdep_hardirqs_on_prepare+0x28b/0x400 kernel/locking/lockdep.c:4049
trace_hardirqs_on+0x5b/0x1c0 kernel/trace/trace_preemptirq.c:49
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x42/0x50 kernel/locking/spinlock.c:191
extract_crng drivers/char/random.c:1026 [inline]
_get_random_bytes+0x229/0x670 drivers/char/random.c:1562
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:538 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:568 [inline]
nsim_dev_trap_report_work+0x740/0xbd0 drivers/net/netdevsim/dev.c:609
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

---
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Next message: Martin Cerveny: "Re: [PATCH v2 0/6] ARM: dts: sun8i: v3s: Enable video decoder"
Previous message: Wen Gong: "Re: drivers/net/wireless/ath/ath10k/sdio.c:2234:2: warning: Non-boolean value returned from function returning bool"
Next in thread: Xiaoguang Wang: "Re: INFO: task can't die in io_sq_thread_stop"
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