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Date: Fri, 30 Oct 2020 11:01:17 +0100
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Hillf Danton <hdanton@...a.com>,
syzbot <syzbot+107dd59d1efcaf3ffca4@...kaller.appspotmail.com>,
io-uring@...r.kernel.org, Kees Cook <keescook@...omium.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>, sgarzare@...hat.com,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
Al Viro <viro@...iv.linux.org.uk>
Subject: Re: INFO: task hung in io_uring_setup
On Thu, Sep 3, 2020 at 1:44 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> 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@...hat.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@...kaller.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)?
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.
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