Re: INFO: task hung in io_uring_setup

[Jens Axboe <axboe@kernel.dk>]

On 9/3/20 5:15 AM, Hillf Danton wrote:
> 
> Thu, 03 Sep 2020 01:38:15 -0700
>> syzbot found the following issue on:
>>
>> HEAD commit:    4442749a Add linux-next specific files for 20200902
>> git tree:       linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=12f9e915900000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=39134fcec6c78e33
>> dashboard link: https://syzkaller.appspot.com/bug?extid=107dd59d1efcaf3ffca4
>> compiler:       gcc (GCC) 10.1.0-syz 20200507
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11594671900000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=111ca835900000
>>
>> The issue was bisected to:
>>
>> commit dfe127799f8e663c7e3e48b5275ca538b278177b
>> Author: Stefano Garzarella <sgarzare@redhat.com>
>> Date:   Thu Aug 27 14:58:31 2020 +0000
>>
>>     io_uring: allow disabling rings during the creation
>>
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11bc66c1900000
>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13bc66c1900000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15bc66c1900000
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+107dd59d1efcaf3ffca4@syzkaller.appspotmail.com
>> Fixes: dfe127799f8e ("io_uring: allow disabling rings during the creation")
>>
>> INFO: task syz-executor047:6853 blocked for more than 143 seconds.
>>       Not tainted 5.9.0-rc3-next-20200902-syzkaller #0
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> task:syz-executor047 state:D stack:28104 pid: 6853 ppid:  6847 flags:0x00004000
>> Call Trace:
>>  context_switch kernel/sched/core.c:3777 [inline]
>>  __schedule+0xea9/0x2230 kernel/sched/core.c:4526
>>  schedule+0xd0/0x2a0 kernel/sched/core.c:4601
>>  schedule_timeout+0x1d8/0x250 kernel/time/timer.c:1855
>>  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
>>  io_sq_thread_stop fs/io_uring.c:6906 [inline]
>>  io_finish_async fs/io_uring.c:6920 [inline]
>>  io_sq_offload_create fs/io_uring.c:7595 [inline]
>>  io_uring_create fs/io_uring.c:8671 [inline]
>>  io_uring_setup+0x1495/0x29a0 fs/io_uring.c:8744
>>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> RIP: 0033:0x440299
>> Code: Bad RIP value.
>> RSP: 002b:00007ffc57cff668 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9
>> RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440299
>> RDX: 0000000000400b40 RSI: 0000000020000100 RDI: 0000000000003ffe
>> RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
>> R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000401aa0
>> R13: 0000000000401b30 R14: 0000000000000000 R15: 0000000000000000
>> INFO: task io_uring-sq:6854 blocked for more than 143 seconds.
>>       Not tainted 5.9.0-rc3-next-20200902-syzkaller #0
>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> task:io_uring-sq     state:D stack:31200 pid: 6854 ppid:     2 flags:0x00004000
>> Call Trace:
>>  context_switch kernel/sched/core.c:3777 [inline]
>>  __schedule+0xea9/0x2230 kernel/sched/core.c:4526
>>  schedule+0xd0/0x2a0 kernel/sched/core.c:4601
>>  schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:4660
>>  kthread+0x2ac/0x4a0 kernel/kthread.c:285
>>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>>
>> Showing all locks held in the system:
>> 1 lock held by khungtaskd/1174:
>>  #0: ffffffff89c67980 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:5829
>> 3 locks held by in:imklog/6525:
>>  #0: ffff8880a3de2df0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:930
>>  #1: ffff8880907d8968 (&mm->mmap_lock#2){++++}-{3:3}, at: rq_lock kernel/sched/sched.h:1292 [inline]
>>  #1: ffff8880907d8968 (&mm->mmap_lock#2){++++}-{3:3}, at: ttwu_queue kernel/sched/core.c:2698 [inline]
>>  #1: ffff8880907d8968 (&mm->mmap_lock#2){++++}-{3:3}, at: try_to_wake_up+0x52b/0x12b0 kernel/sched/core.c:2978
>>  #2: ffff8880ae620ec8 (&per_cpu_ptr(group->pcpu, cpu)->seq){-.-.}-{0:0}, at: psi_task_switch+0x2fb/0x400 kernel/sched/psi.c:833
>>
>> =============================================
>>
>> NMI backtrace for cpu 1
>> CPU: 1 PID: 1174 Comm: khungtaskd Not tainted 5.9.0-rc3-next-20200902-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+0x198/0x1fd lib/dump_stack.c:118
>>  nmi_cpu_backtrace.cold+0x44/0xd7 lib/nmi_backtrace.c:105
>>  nmi_trigger_cpumask_backtrace+0x1b3/0x223 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:339
>>  kthread+0x3b5/0x4a0 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: 3901 Comm: systemd-journal Not tainted 5.9.0-rc3-next-20200902-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> RIP: 0010:unwind_next_frame+0x139a/0x1f90 arch/x86/kernel/unwind_orc.c:607
>> Code: 49 39 47 28 0f 85 3e f0 ff ff 80 3d df 2c 84 09 00 0f 85 31 f0 ff ff e9 06 18 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 14 24 <48> c1 ea 03 80 3c 02 00 0f 85 02 08 00 00 49 8d 7f 08 49 8b 6f 38
>> RSP: 0018:ffffc900040475f8 EFLAGS: 00000246
>> RAX: dffffc0000000000 RBX: 1ffff92000808ec7 RCX: 1ffff92000808ee2
>> RDX: ffffc90004047708 RSI: ffffc90004047aa8 RDI: ffffc90004047aa8
>> RBP: 0000000000000001 R08: ffffffff8b32a670 R09: 0000000000000001
>> R10: 000000000007201e R11: 0000000000000001 R12: ffffc90004047ac8
>> R13: ffffc90004047705 R14: ffffc90004047720 R15: ffffc900040476d0
>> FS:  00007efc659ac8c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007efc62d51000 CR3: 0000000093d6a000 CR4: 00000000001506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  arch_stack_walk+0x81/0xf0 arch/x86/kernel/stacktrace.c:25
>>  stack_trace_save+0x8c/0xc0 kernel/stacktrace.c:123
>>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
>>  kasan_set_track mm/kasan/common.c:56 [inline]
>>  __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
>>  slab_post_alloc_hook mm/slab.h:517 [inline]
>>  slab_alloc mm/slab.c:3312 [inline]
>>  kmem_cache_alloc+0x13a/0x3a0 mm/slab.c:3482
>>  kmem_cache_zalloc include/linux/slab.h:656 [inline]
>>  __alloc_file+0x21/0x350 fs/file_table.c:101
>>  alloc_empty_file+0x6d/0x170 fs/file_table.c:151
>>  path_openat+0xe3/0x2730 fs/namei.c:3354
>>  do_filp_open+0x17e/0x3c0 fs/namei.c:3395
>>  do_sys_openat2+0x16d/0x420 fs/open.c:1168
>>  do_sys_open fs/open.c:1184 [inline]
>>  __do_sys_open fs/open.c:1192 [inline]
>>  __se_sys_open fs/open.c:1188 [inline]
>>  __x64_sys_open+0x119/0x1c0 fs/open.c:1188
>>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Add wakeup to make sure the wait for completion will be completed.
> 
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6903,6 +6903,7 @@ static int io_sqe_files_unregister(struc
>  static void io_sq_thread_stop(struct io_ring_ctx *ctx)
>  {
>  	if (ctx->sqo_thread) {
> +		wake_up_process(ctx->sqo_thread);
>  		wait_for_completion(&ctx->sq_thread_comp);
>  		/*
>  		 * The park is a bit of a work-around, without it we get

Yeah this looks reasonable, if the thread is attempted stopped if it
was created de-activated and never started.

Needs a comment to that effect. Care to add that and send it as a
properly formatted patch (with commit message, etc)?

-- 
Jens Axboe