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    SubjectINFO: task hung in xlog_grant_head_check
    From
    Hello,

    syzbot found the following crash on:

    HEAD commit: 203ec2fed17a Merge tag 'armsoc-fixes' of git://git.kernel...
    git tree: upstream
    console output: https://syzkaller.appspot.com/x/log.txt?x=11c1ad77800000
    kernel config: https://syzkaller.appspot.com/x/.config?x=f3b4e30da84ec1ed
    dashboard link: https://syzkaller.appspot.com/bug?extid=568245b88fbaedcb1959
    compiler: gcc (GCC) 8.0.1 20180413 (experimental)
    syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=122c7427800000
    C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10387057800000

    IMPORTANT: if you fix the bug, please add the following tag to the commit:
    Reported-by: syzbot+568245b88fbaedcb1959@syzkaller.appspotmail.com

    (ptrval): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 ................
    (ptrval): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    00 ................
    XFS (loop0): metadata I/O error in "xfs_trans_read_buf_map" at daddr 0x2
    len 1 error 117
    XFS (loop0): xfs_imap_lookup: xfs_ialloc_read_agi() returned error -117,
    agno 0
    XFS (loop0): failed to read root inode
    INFO: task syz-executor060:4501 blocked for more than 120 seconds.
    Not tainted 4.17.0-rc5+ #60
    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
    syz-executor060 D17168 4501 4499 0x00000000
    Call Trace:
    context_switch kernel/sched/core.c:2859 [inline]
    __schedule+0x801/0x1e30 kernel/sched/core.c:3501
    schedule+0xef/0x430 kernel/sched/core.c:3545
    xlog_grant_head_wait+0x260/0xf80 fs/xfs/xfs_log.c:275
    xlog_grant_head_check+0x4d6/0x550 fs/xfs/xfs_log.c:337
    xfs_log_reserve+0x398/0xd20 fs/xfs/xfs_log.c:466
    xfs_log_unmount_write+0x2c4/0xfb0 fs/xfs/xfs_log.c:885
    xfs_log_quiesce+0xf9/0x130 fs/xfs/xfs_log.c:1011
    xfs_log_unmount+0x22/0xb0 fs/xfs/xfs_log.c:1025
    xfs_log_mount_cancel+0x44/0x60 fs/xfs/xfs_log.c:828
    xfs_mountfs+0x17d9/0x2b80 fs/xfs/xfs_mount.c:1041
    xfs_fs_fill_super+0xdef/0x1560 fs/xfs/xfs_super.c:1734
    mount_bdev+0x30c/0x3e0 fs/super.c:1164
    xfs_fs_mount+0x34/0x40 fs/xfs/xfs_super.c:1801
    mount_fs+0xae/0x328 fs/super.c:1267
    vfs_kern_mount.part.34+0xd4/0x4d0 fs/namespace.c:1037
    vfs_kern_mount fs/namespace.c:1027 [inline]
    do_new_mount fs/namespace.c:2518 [inline]
    do_mount+0x564/0x3070 fs/namespace.c:2848
    ksys_mount+0x12d/0x140 fs/namespace.c:3064
    __do_sys_mount fs/namespace.c:3078 [inline]
    __se_sys_mount fs/namespace.c:3075 [inline]
    __x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
    do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
    entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x442d9a
    RSP: 002b:00007ffc7a9dde88 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
    RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000442d9a
    RDX: 0000000020000040 RSI: 0000000020000100 RDI: 00007ffc7a9dde90
    RBP: 0000000000000004 R08: 00000000200001c0 R09: 000000000000000a
    R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000401c00
    R13: 0000000000401c90 R14: 0000000000000000 R15: 0000000000000000

    Showing all locks held in the system:
    2 locks held by khungtaskd/893:
    #0: (ptrval) (rcu_read_lock){....}, at:
    check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
    #0: (ptrval) (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60
    kernel/hung_task.c:249
    #1: (ptrval) (tasklist_lock){.+.+}, at:
    debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
    1 lock held by rsyslogd/4384:
    #0: (ptrval) (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1a9/0x1e0
    fs/file.c:766
    2 locks held by getty/4474:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4475:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4476:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4477:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4478:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4479:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    2 locks held by getty/4480:
    #0: (ptrval) (&tty->ldisc_sem){++++}, at:
    ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
    #1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
    n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
    1 lock held by syz-executor060/4501:
    #0: (ptrval) (&type->s_umount_key#36/1){+.+.}, at: alloc_super
    fs/super.c:213 [inline]
    #0: (ptrval) (&type->s_umount_key#36/1){+.+.}, at:
    sget_userns+0x2dd/0xf00 fs/super.c:506

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

    NMI backtrace for cpu 0
    CPU: 0 PID: 893 Comm: khungtaskd Not tainted 4.17.0-rc5+ #60
    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+0x1b9/0x294 lib/dump_stack.c:113
    nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
    nmi_trigger_cpumask_backtrace+0x151/0x192 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+0xc10/0xf60 kernel/hung_task.c:249
    kthread+0x345/0x410 kernel/kthread.c:240
    ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
    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:54


    ---
    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.
    syzbot can test patches for this bug, for details see:
    https://goo.gl/tpsmEJ#testing-patches

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