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Date:   Mon, 1 Jul 2019 23:00:30 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     syzbot <syzbot+94324416c485d422fe15@...kaller.appspotmail.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        viro@...iv.linux.org.uk
Subject: Re: INFO: task hung in io_uring_release

Jens, any idea about this?

On Mon, Jun 24, 2019 at 01:21:06AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    bed3c0d8 Merge tag 'for-5.2-rc5-tag' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1418bf0aa00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=28ec3437a5394ee0
> dashboard link: https://syzkaller.appspot.com/bug?extid=94324416c485d422fe15
> compiler:       clang version 9.0.0 (/home/glider/llvm/clang
> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+94324416c485d422fe15@...kaller.appspotmail.com
> 
> INFO: task syz-executor.5:8634 blocked for more than 143 seconds.
>       Not tainted 5.2.0-rc5+ #3
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor.5  D25632  8634   8224 0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:2818 [inline]
>  __schedule+0x658/0x9e0 kernel/sched/core.c:3445
>  schedule+0x131/0x1d0 kernel/sched/core.c:3509
>  schedule_timeout+0x9a/0x2b0 kernel/time/timer.c:1783
>  do_wait_for_common+0x35e/0x5a0 kernel/sched/completion.c:83
>  __wait_for_common kernel/sched/completion.c:104 [inline]
>  wait_for_common kernel/sched/completion.c:115 [inline]
>  wait_for_completion+0x47/0x60 kernel/sched/completion.c:136
>  kthread_stop+0xb4/0x150 kernel/kthread.c:559
>  io_sq_thread_stop fs/io_uring.c:2252 [inline]
>  io_finish_async fs/io_uring.c:2259 [inline]
>  io_ring_ctx_free fs/io_uring.c:2770 [inline]
>  io_ring_ctx_wait_and_kill+0x268/0x880 fs/io_uring.c:2834
>  io_uring_release+0x5d/0x70 fs/io_uring.c:2842
>  __fput+0x2e4/0x740 fs/file_table.c:280
>  ____fput+0x15/0x20 fs/file_table.c:313
>  task_work_run+0x17e/0x1b0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:185 [inline]
>  exit_to_usermode_loop arch/x86/entry/common.c:168 [inline]
>  prepare_exit_to_usermode+0x402/0x4f0 arch/x86/entry/common.c:199
>  syscall_return_slowpath+0x110/0x440 arch/x86/entry/common.c:279
>  do_syscall_64+0x126/0x140 arch/x86/entry/common.c:304
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x412fb1
> Code: 80 3b 7c 0f 84 c7 02 00 00 c7 85 d0 00 00 00 00 00 00 00 48 8b 05 cf
> a6 24 00 49 8b 14 24 41 b9 cb 2a 44 00 48 89 ee 48 89 df <48> 85 c0 4c 0f 45
> c8 45 31 c0 31 c9 e8 0e 5b 00 00 85 c0 41 89 c7
> RSP: 002b:00007ffe7ee6a180 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000412fb1
> RDX: 0000001b2d920000 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 0000000000000001 R08: 00000000f3a3e1f8 R09: 00000000f3a3e1fc
> R10: 00007ffe7ee6a260 R11: 0000000000000293 R12: 000000000075c9a0
> R13: 000000000075c9a0 R14: 0000000000024c00 R15: 000000000075bf2c
> 
> Showing all locks held in the system:
> 1 lock held by khungtaskd/1043:
>  #0: 00000000ec789630 (rcu_read_lock){....}, at: rcu_lock_acquire+0x4/0x30
> include/linux/rcupdate.h:207
> 1 lock held by rsyslogd/8054:
>  #0: 00000000a1730567 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x243/0x2e0
> fs/file.c:801
> 2 locks held by getty/8167:
>  #0: 000000000d85b796 (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 000000006ecd2335 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8168:
>  #0: 000000005c58bd1f (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 00000000158ead38 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8169:
>  #0: 000000003d373884 (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 0000000026014169 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8170:
>  #0: 00000000ba3eabbd (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 0000000003284ce2 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8171:
>  #0: 000000009fcb2c0e (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 00000000ac5d0da7 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8172:
>  #0: 000000003f4e772c (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 000000000c930b31 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 2 locks held by getty/8173:
>  #0: 000000002a3615cf (&tty->ldisc_sem){++++}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:272
>  #1: 00000000dd5c3618 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x2ee/0x1c80 drivers/tty/n_tty.c:2156
> 
> =============================================
> 
> NMI backtrace for cpu 0
> CPU: 0 PID: 1043 Comm: khungtaskd Not tainted 5.2.0-rc5+ #3
> 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+0x1d8/0x2f8 lib/dump_stack.c:113
>  nmi_cpu_backtrace+0x89/0x160 lib/nmi_backtrace.c:101
>  nmi_trigger_cpumask_backtrace+0x125/0x230 lib/nmi_backtrace.c:62
>  arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
>  trigger_all_cpu_backtrace+0x17/0x20 include/linux/nmi.h:146
>  check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
>  watchdog+0xbb9/0xbd0 kernel/hung_task.c:289
>  kthread+0x325/0x350 kernel/kthread.c:255
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 PID: 2546 Comm: kworker/u4:4 Not tainted 5.2.0-rc5+ #3
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: bat_events batadv_nc_worker
> RIP: 0010:__read_once_size include/linux/compiler.h:194 [inline]
> RIP: 0010:arch_atomic_read arch/x86/include/asm/atomic.h:31 [inline]
> RIP: 0010:atomic_read include/asm-generic/atomic-instrumented.h:27 [inline]
> RIP: 0010:rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:292 [inline]
> RIP: 0010:rcu_is_watching+0x62/0xa0 kernel/rcu/tree.c:872
> Code: 4c 89 f7 e8 70 50 4c 00 48 c7 c3 b8 5f 03 00 49 03 1e 48 89 df be 04
> 00 00 00 e8 89 25 4c 00 48 89 d8 48 c1 e8 03 42 8a 04 38 <84> c0 75 1e 8b 03
> 65 ff 0d 5d 72 9f 7e 74 0c 83 e0 02 d1 e8 5b 41
> RSP: 0018:ffff8880a10ffbe8 EFLAGS: 00000a02
> RAX: 1ffff11015d66b00 RBX: ffff8880aeb35fb8 RCX: ffffffff81628ad7
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff8880aeb35fb8
> RBP: ffff8880a10ffc00 R08: dffffc0000000000 R09: ffffed1015d66bf8
> R10: ffffed1015d66bf8 R11: 1ffff11015d66bf7 R12: dffffc0000000000
> R13: ffff8880a93c9b00 R14: ffffffff8881f258 R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000c434bbb720 CR3: 000000008e6fa000 CR4: 00000000001406e0
> Call Trace:
>  rcu_read_lock include/linux/rcupdate.h:594 [inline]
>  batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:407 [inline]
>  batadv_nc_worker+0x115/0x600 net/batman-adv/network-coding.c:718
>  process_one_work+0x814/0x1130 kernel/workqueue.c:2269
>  worker_thread+0xc01/0x1640 kernel/workqueue.c:2415
>  kthread+0x325/0x350 kernel/kthread.c:255
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> 
> 
> ---
> This bug 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@...glegroups.com.
> 
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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