Re: [syzbot] INFO: task hung in __io_uring_cancel

[Pavel Begunkov]

On 4/19/21 10:10 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    1216f02e Add linux-next specific files for 20210415
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=130bbeded00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3491b04113499f81
> dashboard link: https://syzkaller.appspot.com/bug?extid=47fc00967b06a3019bd2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14734dc5d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16dfaf65d00000

The repro looks pretty much like sqpoll-exit-hang test and issues
that were just recently fixed.

#syz test: git://git.kernel.dk/linux-block for-5.13/io_uring

> 
> The issue was bisected to:
> 
> commit d9d05217cb6990b9a56e13b56e7a1b71e2551f6c
> Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
> Date:   Fri Jan 8 20:57:25 2021 +0000
> 
>     io_uring: stop SQPOLL submit on creator's death
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11b86f9ad00000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13b86f9ad00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=15b86f9ad00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+47fc00967b06a3019bd2@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: d9d05217cb69 ("io_uring: stop SQPOLL submit on creator's death")
> 
> INFO: task iou-sqp-8700:8701 blocked for more than 143 seconds.
>       Not tainted 5.12.0-rc7-next-20210415-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:iou-sqp-8700    state:D stack:28960 pid: 8701 ppid:  8414 flags:0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:4329 [inline]
>  __schedule+0x917/0x2170 kernel/sched/core.c:5079
>  schedule+0xcf/0x270 kernel/sched/core.c:5158
>  __io_uring_cancel+0x285/0x420 fs/io_uring.c:8977
>  io_uring_files_cancel include/linux/io_uring.h:16 [inline]
>  do_exit+0x299/0x2a70 kernel/exit.c:780
>  io_sq_thread+0x60a/0x1340 fs/io_uring.c:6873
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/1653:
>  #0: ffffffff8bf76560 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6333
> 1 lock held by in:imklog/8133:
>  #0: ffff888013088370 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:990
> 
> =============================================
> 
> NMI backtrace for cpu 1
> CPU: 1 PID: 1653 Comm: khungtaskd Not tainted 5.12.0-rc7-next-20210415-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x141/0x1d7 lib/dump_stack.c:120
>  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:253 [inline]
>  watchdog+0xd3b/0xf50 kernel/hung_task.c:338
>  kthread+0x3b1/0x4a0 kernel/kthread.c:292
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 7 Comm: kworker/0:1 Not tainted 5.12.0-rc7-next-20210415-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events toggle_allocation_gate
> RIP: 0010:__preempt_count_sub arch/x86/include/asm/preempt.h:85 [inline]
> RIP: 0010:preempt_count_sub+0x56/0x150 kernel/sched/core.c:4772
> Code: 85 e4 00 00 00 8b 0d 19 08 e5 0e 85 c9 75 1b 65 8b 05 ae 60 b3 7e 89 c2 81 e2 ff ff ff 7f 39 da 7c 13 81 fb fe 00 00 00 76 63 <f7> db 65 01 1d 91 60 b3 7e 5b c3 e8 4a cd c2 07 85 c0 74 f5 48 c7
> RSP: 0018:ffffc90000cc79f8 EFLAGS: 00000002
> RAX: 0000000080000002 RBX: 0000000000000001 RCX: 0000000000000000
> RDX: 0000000000000002 RSI: ffffffff83e7543f RDI: 0000000000000001
> RBP: ffff8880b9c34a80 R08: 0000000000000002 R09: 000000000000eb19
> R10: ffffffff83e7538c R11: 000000000000003f R12: 0000000000000008
> R13: ffff888140120660 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffa2b511018 CR3: 000000000bc8e000 CR4: 00000000001506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  flush_tlb_mm_range+0x111/0x230 arch/x86/mm/tlb.c:957
>  __text_poke+0x590/0x8c0 arch/x86/kernel/alternative.c:837
>  text_poke_bp_batch+0x3d7/0x560 arch/x86/kernel/alternative.c:1150
>  text_poke_flush arch/x86/kernel/alternative.c:1240 [inline]
>  text_poke_flush arch/x86/kernel/alternative.c:1237 [inline]
>  text_poke_finish+0x16/0x30 arch/x86/kernel/alternative.c:1247
>  arch_jump_label_transform_apply+0x13/0x20 arch/x86/kernel/jump_label.c:122
>  jump_label_update+0x1da/0x400 kernel/jump_label.c:825
>  static_key_enable_cpuslocked+0x1b1/0x260 kernel/jump_label.c:177
>  static_key_enable+0x16/0x20 kernel/jump_label.c:190
>  toggle_allocation_gate mm/kfence/core.c:610 [inline]
>  toggle_allocation_gate+0xbf/0x2e0 mm/kfence/core.c:602
>  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.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

-- 
Pavel Begunkov