INFO: task hung in io_uring_setup

[syzbot]

Hello,

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 <sgar...@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+107dd5...@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
RIP: 0033:0x7efc64f3c840
Code: 73 01 c3 48 8b 0d 68 77 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 89 bb 20 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e f6 ff ff 48 89 04 24
RSP: 002b:00007ffc45e60f18 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007ffc45e61220 RCX: 00007efc64f3c840
RDX: 00000000000001a0 RSI: 0000000000080042 RDI: 00005626d683e6d0
RBP: 000000000000000d R08: 000000000000c0ff R09: 00000000ffffffff
R10: 0000000000000069 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00005626d6831040 R14: 00007ffc45e611e0 R15: 00005626d683e720


---
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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

[Hillf Danton]

Thu, 03 Sep 2020 01:38:15 -0700

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

[Jens Axboe]

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

[Dmitry Vyukov]

What happened with this fix?
The bug is marked as fixed with commit "io_uring: fix task hung in
io_uring_setup":
https://syzkaller.appspot.com/bug?id=a2b6779df9f5006318875364e0f18cc3af14fa60
but this commit cannot be found in any tree.

[Jens Axboe]

I don't think Hillf ever sent in that patch, but it did get corrected as
part of:

commit 7e84e1c7566a1df470a9e1f49d3db2ce311261a4
Author: Stefano Garzarella <sgar...@redhat.com>
Date: Thu Aug 27 16:58:31 2020 +0200

io_uring: allow disabling rings during the creation

which should have been done as a separate patch. I'll queue one up for
-stable.

--
Jens Axboe

[Dmitry Vyukov]

Thanks.

Let's tell syzbot that this is not an issue anymore:

#syz fix: io_uring: allow disabling rings during the creation

[Hillf Danton]

Hi Jens

You can find what I sent before 4 Sep 2020 at [1]

[1] https://lore.kernel.org/lkml/20200907084327.b2vyca3tbvkeahhx@steredhat/

From: Stefano Garzarella <sgar...@redhat.com>
To: Hillf Danton <hda...@sina.com>
Cc: Jens Axboe <ax...@kernel.dk>,
io-u...@vger.kernel.org, linux-...@vger.kernel.org,
linux-...@vger.kernel.org, syzkall...@googlegroups.com,
vi...@zeniv.linux.org.uk,
syzbot+107dd5...@syzkaller.appspotmail.com,
Kees Cook <kees...@chromium.org>
Subject: Re: [PATCH next] io_uring: fix task hung in io_uring_setup
Date: Mon, 7 Sep 2020 10:43:27 +0200
Message-ID: <20200907084327.b2vyca3tbvkeahhx@steredhat> (raw)
In-Reply-To: <20200903132119....@sina.com>

> >
> > commit 7e84e1c7566a1df470a9e1f49d3db2ce311261a4
> > Author: Stefano Garzarella <sgar...@redhat.com>
> > Date: Thu Aug 27 16:58:31 2020 +0200

And the difference between this Date tag and the timestamp in thread [1]
indicates a glitch somewhere in the next tree.