Hello,
syzbot found the following crash on:
HEAD commit: 47350a9f ANDROID: x86_64_cuttlefish_defconfig: Enable lz4 ..
git tree: android-4.14
console output:
https://syzkaller.appspot.com/x/log.txt?x=146b2d1e400000
kernel config:
https://syzkaller.appspot.com/x/.config?x=10d236078f3378a3
dashboard link:
https://syzkaller.appspot.com/bug?extid=40a29aedacb650561903
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:
https://syzkaller.appspot.com/x/repro.syz?x=1527ca7a400000
C reproducer:
https://syzkaller.appspot.com/x/repro.c?x=1545de3e400000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by:
syzbot+40a29a...@syzkaller.appspotmail.com
INFO: task syz-executor071:2056 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D27816 2056 2054 0x00000000
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
lo_open+0x17/0xa0 drivers/block/loop.c:1592
__blkdev_get+0x267/0xe50 fs/block_dev.c:1467
blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
do_dentry_open+0x426/0xda0 fs/open.c:764
vfs_open+0x11c/0x210 fs/open.c:878
do_last fs/namei.c:3408 [inline]
path_openat+0x4eb/0x23a0 fs/namei.c:3550
do_filp_open+0x197/0x270 fs/namei.c:3584
do_sys_open+0x2ef/0x580 fs/open.c:1071
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x401260
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000401260
RDX: 00007ffe2817f8ca RSI: 0000000000000002 RDI: 00007ffe2817f8c0
RBP: 00000000006cc018 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor071:2058 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29656 2058 2055 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
loop_control_ioctl+0x180/0x310 drivers/block/loop.c:1965
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441359
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441359
RDX: 0000000000000002 RSI: 0000000000004c81 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000217 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor071:2059 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D28376 2059 2057 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
blkdev_reread_part+0x18/0x30 block/ioctl.c:192
loop_reread_partitions+0x72/0x80 drivers/block/loop.c:614
loop_set_status+0xa84/0xf40 drivers/block/loop.c:1169
loop_set_status64+0x8d/0xe0 drivers/block/loop.c:1287
lo_ioctl+0x3cd/0x17d0 drivers/block/loop.c:1400
__blkdev_driver_ioctl block/ioctl.c:297 [inline]
blkdev_ioctl+0x57d/0x18c0 block/ioctl.c:594
block_ioctl+0xd9/0x120 fs/block_dev.c:1873
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441267
RSP: 002b:00007ffe2817f668 EFLAGS: 00000202 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000441267
RDX: 00007ffe2817f700 RSI: 0000000000004c04 RDI: 0000000000000005
RBP: 0000000020000228 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000202 R12: 0000000000000005
R13: 0000000000000004 R14: 0000000000000004 R15: 0000000000000000
INFO: task blkid:2060 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid D29000 2060 455 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
lo_open+0x17/0xa0 drivers/block/loop.c:1592
__blkdev_get+0x267/0xe50 fs/block_dev.c:1467
blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
do_dentry_open+0x426/0xda0 fs/open.c:764
vfs_open+0x11c/0x210 fs/open.c:878
do_last fs/namei.c:3408 [inline]
path_openat+0x4eb/0x23a0 fs/namei.c:3550
do_filp_open+0x197/0x270 fs/namei.c:3584
do_sys_open+0x2ef/0x580 fs/open.c:1071
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x7fae6af4f120
RSP: 002b:00007ffe8acd6588 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fae6af4f120
RDX: 00007ffe8acd7f34 RSI: 0000000000000000 RDI: 00007ffe8acd7f34
RBP: 0000000000000000 R08: 0000000000000078 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000001c8e030
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000005
INFO: task syz-executor071:2068 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29656 2068 2062 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441359
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441359
RDX: 0000000000441359 RSI: 0000000000004c82 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000002066880 R11: 0000000000000213 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor071:2069 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29064 2069 2063 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
do_dentry_open+0x426/0xda0 fs/open.c:764
vfs_open+0x11c/0x210 fs/open.c:878
do_last fs/namei.c:3408 [inline]
path_openat+0x4eb/0x23a0 fs/namei.c:3550
do_filp_open+0x197/0x270 fs/namei.c:3584
do_sys_open+0x2ef/0x580 fs/open.c:1071
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x401260
RSP: 002b:00007ffe2817f668 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000401260
RDX: 00007ffe2817f7fa RSI: 0000000000000002 RDI: 00007ffe2817f7f0
RBP: 0000000020000228 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000004 R14: 0000000000000004 R15: 0000000000000000
INFO: task syz-executor071:2070 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29656 2070 2064 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441359
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441359
RDX: 0000000000441359 RSI: 0000000000004c82 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000002066880 R11: 0000000000000213 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor071:2071 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29656 2071 2066 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441359
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441359
RDX: 0000000000441359 RSI: 0000000000004c82 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000002066880 R11: 0000000000000213 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor071:2072 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor071 D29120 2072 2065 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1a0/0x1030 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7e/0xb0 fs/ioctl.c:692
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x441359
RSP: 002b:00007ffe2817f8a8 EFLAGS: 00000213 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441359
RDX: 0000000000441359 RSI: 0000000000004c82 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000002066880 R11: 0000000000000213 R12: 0000000000402190
R13: 0000000000402220 R14: 0000000000000000 R15: 0000000000000000
INFO: task blkid:2077 blocked for more than 140 seconds.
Not tainted 4.14.67+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid D28280 2077 2073 0x00000004
Call Trace:
schedule+0x7f/0x1b0 kernel/sched/core.c:3490
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3548
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x521/0x1480 kernel/locking/mutex.c:893
lo_open+0x17/0xa0 drivers/block/loop.c:1592
__blkdev_get+0x267/0xe50 fs/block_dev.c:1467
blkdev_get+0x97/0x8c0 fs/block_dev.c:1604
blkdev_open+0x1bd/0x240 fs/block_dev.c:1762
do_dentry_open+0x426/0xda0 fs/open.c:764
vfs_open+0x11c/0x210 fs/open.c:878
do_last fs/namei.c:3408 [inline]
path_openat+0x4eb/0x23a0 fs/namei.c:3550
do_filp_open+0x197/0x270 fs/namei.c:3584
do_sys_open+0x2ef/0x580 fs/open.c:1071
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x7f9a3e302120
RSP: 002b:00007fffa8496548 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9a3e302120
RDX: 00007fffa8496f34 RSI: 0000000000000000 RDI: 00007fffa8496f34
RBP: 0000000000000000 R08: 0000000000000078 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000024fd030
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000005
Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: (tasklist_lock){.+.+}, at: [<ffffffff89c01847>]
debug_show_all_locks+0x74/0x20f kernel/locking/lockdep.c:4541
1 lock held by rsyslogd/1799:
#0: (&f->f_pos_lock){+.+.}, at: [<ffffffff89fbcab2>]
__fdget_pos+0xa2/0xc0 fs/file.c:768
2 locks held by getty/1895:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff8a71c500>]
tty_ldisc_ref_wait+0x20/0x80 drivers/tty/tty_ldisc.c:275
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff8a717a7f>]
n_tty_read+0x1ff/0x15e0 drivers/tty/n_tty.c:2142
2 locks held by syz-executor071/2056:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by syz-executor071/2058:
#0: (loop_index_mutex){+.+.}, at: [<ffffffff8a7ce641>]
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
#1: (&lo->lo_ctl_mutex#2){+.+.}, at: [<ffffffff8a7ce750>]
loop_control_ioctl+0x180/0x310 drivers/block/loop.c:1965
2 locks held by syz-executor071/2059:
#0: (&lo->lo_ctl_mutex/1){+.+.}, at: [<ffffffff8a7cb8d5>]
lo_ioctl+0x85/0x17d0 drivers/block/loop.c:1373
#1: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a4fd838>]
blkdev_reread_part+0x18/0x30 block/ioctl.c:192
2 locks held by blkid/2060:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
1 lock held by syz-executor071/2068:
#0: (loop_index_mutex){+.+.}, at: [<ffffffff8a7ce641>]
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
1 lock held by syz-executor071/2069:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
1 lock held by syz-executor071/2070:
#0: (loop_index_mutex){+.+.}, at: [<ffffffff8a7ce641>]
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
1 lock held by syz-executor071/2071:
#0: (loop_index_mutex){+.+.}, at: [<ffffffff8a7ce641>]
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
1 lock held by syz-executor071/2072:
#0: (loop_index_mutex){+.+.}, at: [<ffffffff8a7ce641>]
loop_control_ioctl+0x71/0x310 drivers/block/loop.c:1951
2 locks held by blkid/2077:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by blkid/2078:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by blkid/2079:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by blkid/2080:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by blkid/2081:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
2 locks held by blkid/2085:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffff8a0188c3>]
__blkdev_get+0xf3/0xe50 fs/block_dev.c:1452
#1: (loop_index_mutex){+.+.}, at: [<ffffffff8a7c7107>] lo_open+0x17/0xa0
drivers/block/loop.c:1592
=============================================
NMI backtrace for cpu 0
CPU: 0 PID: 23 Comm: khungtaskd Not tainted 4.14.67+ #1
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x11b lib/dump_stack.c:53
nmi_cpu_backtrace.cold.0+0x18/0x8e lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x121/0x146 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:196 [inline]
watchdog+0x574/0xa70 kernel/hung_task.c:252
kthread+0x348/0x420 kernel/kthread.c:232
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:402
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff8b240572
---
This bug is generated by a bot. It may contain errors.
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches