Date:   Tue, 12 Dec 2017 17:45:38 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot 
        <bot+a444b4083d33277c6e9b4605faf0a79773e29cc5@...kaller.appspotmail.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs@...glegroups.com, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <tom.leiming@...il.com>,
        Omar Sandoval <osandov@...com>, Hannes Reinecke <hare@...e.de>,
        shli@...com
Subject: Re: INFO: task hung in blkdev_put

On Sun, Dec 10, 2017 at 2:38 PM, syzbot
<bot+a444b4083d33277c6e9b4605faf0a79773e29cc5@...kaller.appspotmail.com>
wrote:
> Hello,
>
> syzkaller hit the following crash on
> ad4dac17f9d563b9e34aab78a34293b10993e9b5
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
>
> Unfortunately, I don't have any reproducer for this bug yet.
>
>
> Buffer I/O error on dev loop0, logical block 8, async page read
> INFO: task blkid:16495 blocked for more than 120 seconds.
>       Not tainted 4.15.0-rc2-next-20171208+ #63
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> blkid           D21344 16495   3125 0x80000006
> Call Trace:
>  context_switch kernel/sched/core.c:2800 [inline]
>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>  schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3493
>  __mutex_lock_common kernel/locking/mutex.c:833 [inline]
>  __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893
>  mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>  blkdev_put+0x2a/0x4f0 fs/block_dev.c:1793
>  blkdev_close+0x91/0xc0 fs/block_dev.c:1842
>  __fput+0x333/0x7f0 fs/file_table.c:210
>  ____fput+0x15/0x20 fs/file_table.c:244
>  task_work_run+0x199/0x270 kernel/task_work.c:113
>  exit_task_work include/linux/task_work.h:22 [inline]
>  do_exit+0x9bb/0x1ae0 kernel/exit.c:869
>  do_group_exit+0x149/0x400 kernel/exit.c:972
>  get_signal+0x73f/0x16c0 kernel/signal.c:2337
>  do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:809
>  exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:161
>  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
>  syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
>  entry_SYSCALL_64_fastpath+0x94/0x96
> RIP: 0033:0x7f2117ef9310
> RSP: 002b:00007ffeedf28478 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: fffffffffffffffb RBX: 0000000000002000 RCX: 00007f2117ef9310
> RDX: 0000000000000561 RSI: 0000000000ea2a58 RDI: 0000000000000003
> RBP: 0000000000ea2a30 R08: 0000000000000018 R09: 0000000000168000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000ea1030
> R13: 0000000000000561 R14: 0000000000ea1080 R15: 0000000000ea2a48
>
> Showing all locks held in the system:
> 2 locks held by khungtaskd/672:
>  #0:  (rcu_read_lock){....}, at: [<00000000166545b0>]
> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>  #0:  (rcu_read_lock){....}, at: [<00000000166545b0>] watchdog+0x1c5/0xd60
> kernel/hung_task.c:249
>  #1:  (tasklist_lock){.+.+}, at: [<00000000327f4dad>]
> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
> 1 lock held by rsyslogd/2993:
>  #0:  (&f->f_pos_lock){+.+.}, at: [<000000006eb70b1d>]
> __fdget_pos+0x131/0x1a0 fs/file.c:765
> 2 locks held by getty/3115:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3116:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3117:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3118:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3119:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3120:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3121:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000059fa20b1>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000007035e50d>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 3 locks held by kworker/u4:9/4216:
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> __write_once_size include/linux/compiler.h:212 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> set_work_data kernel/workqueue.c:619 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<0000000064bfb8f2>]
> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>  #1:  ((work_completion)(&(&wb->dwork)->work)){+.+.}, at:
> [<000000009ce31f83>] process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>  #2:  (&type->s_umount_key#25){++++}, at: [<000000008ac62721>]
> trylock_super+0x20/0x100 fs/super.c:395
> 1 lock held by blkid/16495:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<000000007747ddd3>]
> blkdev_put+0x2a/0x4f0 fs/block_dev.c:1793
> 1 lock held by syz-executor3/16557:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<000000007747ddd3>]
> blkdev_put+0x2a/0x4f0 fs/block_dev.c:1793
> 1 lock held by syz-executor7/16620:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000f5d98222>]
> iterate_bdevs+0xc8/0x260 fs/block_dev.c:2145
> 1 lock held by syz-executor7/16640:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000f5d98222>]
> iterate_bdevs+0xc8/0x260 fs/block_dev.c:2145
>
> =============================================
>
> NMI backtrace for cpu 1
> CPU: 1 PID: 672 Comm: khungtaskd Not tainted 4.15.0-rc2-next-20171208+ #63
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:17 [inline]
>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>  nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
>  nmi_trigger_cpumask_backtrace+0x122/0x180 lib/nmi_backtrace.c:62
>  arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
>  trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
>  check_hung_task kernel/hung_task.c:132 [inline]
>  check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
>  watchdog+0x90c/0xd60 kernel/hung_task.c:249
>  kthread+0x37a/0x440 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-rc2-next-20171208+ #63
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__read_once_size include/linux/compiler.h:183 [inline]
> RIP: 0010:atomic_read arch/x86/include/asm/atomic.h:27 [inline]
> RIP: 0010:nr_iowait_cpu+0xbc/0x120 kernel/sched/core.c:2902
> RSP: 0018:ffff8801db207c58 EFLAGS: 00000046
> RAX: 0000000000000000 RBX: ffff8801db22c900 RCX: ffffffff8163cfdd
> RDX: dffffc0000000000 RSI: ffff8801db223540 RDI: ffff8801db207c80
> RBP: ffff8801db207cd8 R08: ffff88021fff801c R09: ffff88021fff8008
> R10: ffff88021fff8010 R11: ffff88021fff801d R12: 1ffff1003b640f8c
> R13: 0000000000000000 R14: ffff8801db2235c8 R15: ffff8801db223540
> FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000147b000 CR3: 00000001cc504000 CR4: 00000000001406f0
> DR0: 0000000020001000 DR1: 0000000020001000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> Call Trace:
>  <IRQ>
>  update_ts_time_stats+0xee/0x1c0 kernel/time/tick-sched.c:504
>  tick_nohz_stop_idle kernel/time/tick-sched.c:518 [inline]
>  tick_nohz_irq_enter kernel/time/tick-sched.c:1104 [inline]
>  tick_irq_enter+0x262/0x390 kernel/time/tick-sched.c:1123
>  irq_enter+0xbd/0xe0 kernel/softirq.c:346
>  scheduler_ipi+0x246/0x830 kernel/sched/core.c:1794
>  smp_reschedule_interrupt+0xe6/0x670 arch/x86/kernel/smp.c:277
>  reschedule_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:944
>  </IRQ>
> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
> RSP: 0018:ffffffff86207d08 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff02
> RAX: dffffc0000000000 RBX: 1ffffffff0c40fa4 RCX: 0000000000000000
> RDX: 1ffffffff0c5975c RSI: 0000000000000001 RDI: ffffffff862cbae0
> RBP: ffffffff86207d08 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffffffff86207dc0 R14: ffffffff869efaa0 R15: 0000000000000000
>  arch_safe_halt arch/x86/include/asm/paravirt.h:93 [inline]
>  default_idle+0xbf/0x430 arch/x86/kernel/process.c:355
>  arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:346
>  default_idle_call+0x36/0x90 kernel/sched/idle.c:98
>  cpuidle_idle_call kernel/sched/idle.c:156 [inline]
>  do_idle+0x24a/0x3b0 kernel/sched/idle.c:246
>  cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:351
>  rest_init+0xed/0xf0 init/main.c:436
>  start_kernel+0x729/0x74f init/main.c:717
>  x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:378
>  x86_64_start_kernel+0x77/0x7a arch/x86/kernel/head64.c:359
>  secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:237
> Code: 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 5d 48
> 8d 7d a8 48 ba 00 00 00 00 00 fc ff df 48 63 83 28 0a 00 00 <48> 89 f9 48 c1
> e9 03 0f b6 14 11 84 d2 74 05 80 fa 03 7e 26 48

+loop maintainers

#syz dup: INFO: task hung in lo_ioctl

> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@...glegroups.com.
> Please credit me with: Reported-by: syzbot <syzkaller@...glegroups.com>
>
> syzbot will keep track of this bug report.
> Once a fix for this bug is merged into any tree, reply to this email with:
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> To mark this as a duplicate of another syzbot report, please reply with:
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