Date:   Tue, 12 Dec 2017 16:33:19 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot 
        <bot+abdba5bc6de135d7622f00756da97998425b6de5@...kaller.appspotmail.com>,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <tom.leiming@...il.com>,
        Omar Sandoval <osandov@...com>, Hannes Reinecke <hare@...e.de>,
        shli@...com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: INFO: task hung in lo_ioctl

On Sun, Dec 10, 2017 at 2:32 PM, syzbot
<bot+abdba5bc6de135d7622f00756da97998425b6de5@...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.
>
>
> INFO: task syz-executor3:12157 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-executor3   D25536 12157   3362 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
>  lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
>  __blkdev_driver_ioctl block/ioctl.c:303 [inline]
>  blkdev_ioctl+0x1759/0x1e00 block/ioctl.c:601
>  block_ioctl+0xea/0x130 fs/block_dev.c:1860
>  vfs_ioctl fs/ioctl.c:46 [inline]
>  do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
>  SYSC_ioctl fs/ioctl.c:701 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>  entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x452a39
> RSP: 002b:00007fd85b57ec58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000758190 RCX: 0000000000452a39
> RDX: 0000000020e67fd8 RSI: 00000000400454ca RDI: 0000000000000016
> RBP: 000000000000005b R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006ee928
> R13: 00000000ffffffff R14: 00007fd85b57f6d4 R15: 0000000000000002
>
> Showing all locks held in the system:
> 2 locks held by khungtaskd/671:
>  #0:  (rcu_read_lock){....}, at: [<0000000053bc3983>]
> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>  #0:  (rcu_read_lock){....}, at: [<0000000053bc3983>] watchdog+0x1c5/0xd60
> kernel/hung_task.c:249
>  #1:  (tasklist_lock){.+.+}, at: [<00000000c2c6381b>]
> debug_show_all_locks+0xd3/0x400 kernel/locking/lockdep.c:4554
> 2 locks held by getty/3115:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3116:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3117:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3118:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3119:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 2 locks held by getty/3120:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 1 lock held by syz-executor3/12157:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000d5130113>]
> lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
> 1 lock held by syz-executor7/12154:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000d5130113>]
> lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
> 1 lock held by syz-executor7/12168:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000d5130113>]
> lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
> 1 lock held by syz-executor5/12216:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000d5130113>]
> lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
> 2 locks held by getty/12231:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000e7f92d1f>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000f15a7c4f>]
> n_tty_read+0x2f2/0x1a10 drivers/tty/n_tty.c:2131
> 1 lock held by blkid/12232:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000d5130113>]
> lo_ioctl+0x8b/0x1b90 drivers/block/loop.c:1355
>
> =============================================
>
> 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:unwind_next_frame.part.6+0x5f1/0xb40 include/linux/compiler.h:183
> RSP: 0018:ffff8801db306e28 EFLAGS: 00000806
> RAX: dffffc0000000000 RBX: ffff8801db306f48 RCX: ffff8801db306ef8
> RDX: ffff8801db306f70 RSI: 1ffff1003b660dcf RDI: ffff8801d9f97f48
> RBP: ffff8801db306f20 R08: ffff8801db306f80 R09: ffff8801d9f88300
> R10: 000000000000000b R11: ffffed003b660df3 R12: 1ffff1003b660dcb
> R13: ffff8801db307490 R14: 1ffff1003b660dcf R15: ffff8801db306f98
> FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000001e5e000 CR3: 00000001cb1b5000 CR4: 00000000001406e0
> DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
> Call Trace:
>  <IRQ>
>  unwind_next_frame+0x3e/0x50 arch/x86/kernel/unwind_frame.c:287
>  __save_stack_trace+0x6e/0xd0 arch/x86/kernel/stacktrace.c:44
>  save_stack_trace+0x1a/0x20 arch/x86/kernel/stacktrace.c:60
>  add_xhlock kernel/locking/lockdep.c:4880 [inline]
>  check_add_xhlock kernel/locking/lockdep.c:4907 [inline]
>  lock_acquire_crosslock kernel/locking/lockdep.c:4979 [inline]
>  __lock_acquire+0x324e/0x47f0 kernel/locking/lockdep.c:3503
>  lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004
>  __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]
>  update_blocked_averages+0x124/0x1b60 kernel/sched/fair.c:7353
>  rebalance_domains+0x145/0xcc0 kernel/sched/fair.c:9122
>  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: 8b 6d 00 4c 89 f6 48 c1 ee 03 80 3c 06 00 0f 85 e9 04 00 00 49 c1 ee
> 03 48 b8 00 00 00 00 00 fc ff df 4c 89 69 80 41 c6 04 06 f8 <e9> 97 fb ff ff
> 80 3d f7 60 6e 05 00 0f 85 fc fc ff ff 49 8d be


This seems to be about loop device, but was mis-attributed to
scheduler. So +loop maintainers.

FTR, mis-attribution in syzbot was fixed in:
https://github.com/google/syzkaller/commit/27f5dfefff3cd00795d9048ecc7bc70965e03ea7

> ---
> 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:
> #syz fix: exact-commit-title
> To mark this as a duplicate of another syzbot report, please reply with:
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> If it's a one-off invalid bug report, please reply with:
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> Note: if the crash happens again, it will cause creation of a new bug
> report.
> Note: all commands must start from beginning of the line in the email body.
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