Date:   Tue, 12 Dec 2017 17:44:59 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot 
        <bot+741bd31dd54b3674f877e45d0f160c041a071424@...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 iterate_bdevs

On Sun, Dec 10, 2017 at 2:38 PM, syzbot
<bot+741bd31dd54b3674f877e45d0f160c041a071424@...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 16, async page read
> INFO: task syz-executor4:12904 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.
> syz-executor4   D24112 12904   3382 0x00000004
> 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
>  iterate_bdevs+0xc8/0x260 fs/block_dev.c:2145
>  sys_sync+0x120/0x1c0 fs/sync.c:117
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x452a39
> RSP: 002b:00007f715cc26c58 EFLAGS: 00000212 ORIG_RAX: 00000000000000a2
> RAX: ffffffffffffffda RBX: 0000000000758020 RCX: 0000000000452a39
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 000000000000035f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f3188
> R13: 00000000ffffffff R14: 00007f715cc276d4 R15: 0000000000000000
>
> Showing all locks held in the system:
> 2 locks held by khungtaskd/671:
>  #0:  (rcu_read_lock){....}, at: [<00000000a246bf4d>]
> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>  #0:  (rcu_read_lock){....}, at: [<00000000a246bf4d>] watchdog+0x1c5/0xd60
> kernel/hung_task.c:249
>  #1:  (tasklist_lock){.+.+}, at: [<0000000028532ec4>]
> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
> 2 locks held by getty/3111:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3112:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3113:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3114:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3115:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3116:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3117:
>  #0:  (&tty->ldisc_sem){++++}, at: [<0000000097fd2331>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<000000003299e4a0>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 3 locks held by kworker/u4:11/4947:
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> __write_once_size include/linux/compiler.h:212 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> atomic_long_set include/asm-generic/atomic-long.h:57 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> set_work_data kernel/workqueue.c:619 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
>  #0:  ((wq_completion)"writeback"){+.+.}, at: [<00000000ece778e7>]
> process_one_work+0xad4/0x1bc0 kernel/workqueue.c:2084
>  #1:  ((work_completion)(&(&wb->dwork)->work)){+.+.}, at:
> [<0000000018dc8804>] process_one_work+0xb2f/0x1bc0 kernel/workqueue.c:2088
>  #2:  (&type->s_umount_key#25){.+.+}, at: [<0000000001171e24>]
> trylock_super+0x20/0x100 fs/super.c:395
> 1 lock held by blkid/12529:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<000000000a2782da>]
> blkdev_put+0x2a/0x4f0 fs/block_dev.c:1793
> 1 lock held by syz-executor4/12904:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000c5a0f02d>]
> iterate_bdevs+0xc8/0x260 fs/block_dev.c:2145
> 1 lock held by syz-executor4/12911:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<00000000c5a0f02d>]
> iterate_bdevs+0xc8/0x260 fs/block_dev.c:2145
> 1 lock held by syz-executor1/12932:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<000000003ffc09e5>]
> __blkdev_get+0x158/0x10e0 fs/block_dev.c:1439
> 1 lock held by syz-executor1/12947:
>  #0:  (&bdev->bd_mutex){+.+.}, at: [<000000003ffc09e5>]
> __blkdev_get+0x158/0x10e0 fs/block_dev.c:1439
>
> =============================================
>
> NMI backtrace for cpu 0
> CPU: 0 PID: 671 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 0 to CPUs 1:
> NMI backtrace for cpu 1
> CPU: 1 PID: 0 Comm: swapper/1 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:lock_acquire+0x63/0x580 kernel/locking/lockdep.c:3993
> RSP: 0018:ffff8801db3072f0 EFLAGS: 00000086
> RAX: ffffed003b660e64 RBX: ffff8801db22c900 RCX: dffffc0000000000
> RDX: ffff8801d9f88300 RSI: 0000000000000000 RDI: ffff8801d9f88b84
> RBP: ffff8801db3073e8 R08: 0000000000000001 R09: 0000000000000000
> R10: 1ffff1003b660e64 R11: 0000000000000001 R12: 0000000000000282
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000001
> FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fbf987cc000 CR3: 00000001d7210000 CR4: 00000000001406e0
> Call Trace:
>  <IRQ>
>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
>  _raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:159
>  rq_lock_irqsave kernel/sched/sched.h:1750 [inline]
>  load_balance+0xb10/0x34c0 kernel/sched/fair.c:8526
>  rebalance_domains+0x786/0xcc0 kernel/sched/fair.c:9161
>  run_rebalance_domains+0x381/0x780 kernel/sched/fair.c:9383
>  __do_softirq+0x29d/0xbb2 kernel/softirq.c:285
>  invoke_softirq kernel/softirq.c:365 [inline]
>  irq_exit+0x1d3/0x210 kernel/softirq.c:405
>  scheduler_ipi+0x32a/0x830 kernel/sched/core.c:1804
>  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:ffff8801d9f97da8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff02
> RAX: dffffc0000000000 RBX: 1ffff1003b3f2fb8 RCX: 0000000000000000
> RDX: 1ffffffff0c5975c RSI: 0000000000000001 RDI: ffffffff862cbae0
> RBP: ffff8801d9f97da8 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
> R13: ffff8801d9f97e60 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
>  start_secondary+0x330/0x460 arch/x86/kernel/smpboot.c:277
>  secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:237
> Code: bd 30 ff ff ff 65 48 8b 14 25 40 be 01 00 48 8d ba 84 08 00 00 48 c7
> 85 38 ff ff ff b3 8a b5 41 48 c7 85 40 ff ff ff 78 d8 f1 85 <48> c7 85 48 ff
> ff ff f0 69 56 81 89 b5 2c ff ff ff 4c 89 cb c7


+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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