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    SubjectINFO: task hung in vivid_stop_generating_vid_cap
    From
    Hello,

    syzbot found the following crash on:

    HEAD commit: 8c60c36d0b8c Add linux-next specific files for 20181019
    git tree: linux-next
    console output: https://syzkaller.appspot.com/x/log.txt?x=1608ccf5400000
    kernel config: https://syzkaller.appspot.com/x/.config?x=ddc97ab84fb1ff2a
    dashboard link: https://syzkaller.appspot.com/bug?extid=06283a66a648cd073885
    compiler: gcc (GCC) 8.0.1 20180413 (experimental)

    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+06283a66a648cd073885@syzkaller.appspotmail.com

    VMExit: intr_info=00000000 errcode=00000000 ilen=00000003
    reason=80000021 qualification=0000000000000003
    IDTVectoring: info=00000000 errcode=00000000
    TSC Offset = 0xfffffe6382838c64
    EPT pointer = 0x00000001c4f5101e
    INFO: task syz-executor4:791 blocked for more than 140 seconds.
    Not tainted 4.19.0-rc8-next-20181019+ #99
    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    syz-executor4 D23272 791 5784 0x00000004
    Call Trace:
    context_switch kernel/sched/core.c:2831 [inline]
    __schedule+0x8cf/0x21d0 kernel/sched/core.c:3480
    schedule+0xfe/0x460 kernel/sched/core.c:3524
    schedule_timeout+0x1cc/0x260 kernel/time/timer.c:1780
    do_wait_for_common kernel/sched/completion.c:83 [inline]
    __wait_for_common kernel/sched/completion.c:104 [inline]
    wait_for_common kernel/sched/completion.c:115 [inline]
    wait_for_completion+0x427/0x8a0 kernel/sched/completion.c:136
    kthread_stop+0x1a4/0x8f0 kernel/kthread.c:550
    vivid_stop_generating_vid_cap+0x2bc/0x93b
    drivers/media/platform/vivid/vivid-kthread-cap.c:919
    vid_cap_stop_streaming+0x8d/0xe0
    drivers/media/platform/vivid/vivid-vid-cap.c:259
    __vb2_queue_cancel+0x171/0xca0
    drivers/media/common/videobuf2/videobuf2-core.c:1668
    vb2_core_streamoff+0x60/0x140
    drivers/media/common/videobuf2/videobuf2-core.c:1804
    __vb2_cleanup_fileio+0x73/0x160
    drivers/media/common/videobuf2/videobuf2-core.c:2325
    vb2_core_queue_release+0x1e/0x80
    drivers/media/common/videobuf2/videobuf2-core.c:2052
    vb2_queue_release drivers/media/common/videobuf2/videobuf2-v4l2.c:672
    [inline]
    _vb2_fop_release+0x1d2/0x2b0
    drivers/media/common/videobuf2/videobuf2-v4l2.c:843
    vb2_fop_release+0x77/0xc0
    drivers/media/common/videobuf2/videobuf2-v4l2.c:857
    vivid_fop_release+0x18e/0x440 drivers/media/platform/vivid/vivid-core.c:474
    v4l2_release+0xfb/0x1a0 drivers/media/v4l2-core/v4l2-dev.c:448
    __fput+0x3bc/0xa70 fs/file_table.c:279
    ____fput+0x15/0x20 fs/file_table.c:312
    task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
    tracehook_notify_resume include/linux/tracehook.h:188 [inline]
    exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
    prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
    syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
    do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x411021
    Code: 4c 89 f6 48 89 c7 48 89 ca 48 89 4c 24 10 4c 89 54 24 08 e8 b1 a3 ff
    ff 48 8b 4c 24 10 41 c6 04 0f 00 4c 8b 7c 24 28 4c 8b 54 <24> 08 45 0f b6
    37 e9 db fc ff ff 0f 1f 40 00 41 80 f8 29 74 7f ba
    RSP: 002b:00007ffebf8f0810 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
    RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000411021
    RDX: 0000001b2ca20000 RSI: 0000000000730430 RDI: 0000000000000003
    RBP: 0000000000000000 R08: 0000000030c04255 R09: 0000000030c04259
    R10: 00007ffebf8f0740 R11: 0000000000000293 R12: 0000000000000000
    R13: 0000000000000001 R14: 0000000000000447 R15: 0000000000000004

    Showing all locks held in the system:
    1 lock held by khungtaskd/1008:
    #0: 00000000b994d395 (rcu_read_lock){....}, at:
    debug_show_all_locks+0xd0/0x424 kernel/locking/lockdep.c:4379
    1 lock held by rsyslogd/5554:
    #0: 0000000064483821 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200
    fs/file.c:766
    2 locks held by getty/5644:
    #0: 0000000088b7a22a (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 000000003463365c (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5645:
    #0: 00000000b07a05bf (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000accbc122 (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5646:
    #0: 000000003b71eb89 (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000e3b18d3f (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5647:
    #0: 00000000c8f2c425 (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000646fd3b6 (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5648:
    #0: 000000004a4ae0cc (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000d9aa1576 (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5649:
    #0: 000000001d616490 (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000865e3bcf (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
    2 locks held by getty/5650:
    #0: 00000000c8214d1d (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
    #1: 00000000782baf35 (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154

    =============================================

    NMI backtrace for cpu 0
    CPU: 0 PID: 1008 Comm: khungtaskd Not tainted 4.19.0-rc8-next-20181019+ #99
    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+0x244/0x39d lib/dump_stack.c:113
    nmi_cpu_backtrace.cold.2+0x5c/0xa1 lib/nmi_backtrace.c:101
    nmi_trigger_cpumask_backtrace+0x1e8/0x22a 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:144 [inline]
    check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
    watchdog+0xb39/0x1050 kernel/hung_task.c:265
    kthread+0x35a/0x440 kernel/kthread.c:246
    ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
    Sending NMI from CPU 0 to CPUs 1:
    NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10
    arch/x86/include/asm/irqflags.h:57


    ---
    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@googlegroups.com.

    syzbot will keep track of this bug report. See:
    https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
    syzbot.

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