INFO: task hung in ctrl_cdev_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b850307b Linux 4.14.184
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17275857100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ddc0f08dd6b981c5
dashboard link: https://syzkaller.appspot.com/bug?extid=69aa38ac3bcbf218af1f
compiler: gcc (GCC) 9.0.0 20181231 (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+69aa38...@syzkaller.appspotmail.com

ubi0: max/mean erase counter: 1/1, WL threshold: 4096, image sequence number: 3168473204
ubi0: available PEBs: 28, total reserved PEBs: 4, PEBs reserved for bad PEB handling: 0
ubi0: background thread "ubi_bgt0d" started, PID 4072
ubi0: detaching mtd0
INFO: task syz-executor.5:4061 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.5 D28896 4061 6359 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f00ac1efc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040046f41 RDI: 0000000000000006
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f00ac1f06d4
INFO: task syz-executor.4:4067 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4 D28800 4067 6358 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f2dbbf91c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000007
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f2dbbf926d4
INFO: task syz-executor.4:4080 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4 D30080 4080 6358 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f2dbbf70c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040046f41 RDI: 0000000000000006
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f2dbbf716d4
INFO: task syz-executor.4:4081 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4 D30080 4081 6358 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f2dbbf4fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040046f41 RDI: 0000000000000006
RBP: 000000000078c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f2dbbf506d4
INFO: task syz-executor.4:4094 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4 D29216 4094 6358 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f2dbbf2ec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000007
RBP: 000000000078c0e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f2dbbf2f6d4
INFO: task syz-executor.3:4063 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D28832 4063 6357 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f275792cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000009
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f275792d6d4
INFO: task syz-executor.3:4070 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D30080 4070 6357 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f275790bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000004
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f275790c6d4
INFO: task syz-executor.3:4079 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D28576 4079 6357 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f27578eac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040046f41 RDI: 0000000000000008
RBP: 000000000078c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f27578eb6d4
INFO: task syz-executor.3:4083 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D30080 4083 6357 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f27578c9c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000003
RBP: 000000000078c0e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f27578ca6d4
INFO: task syz-executor.3:4087 blocked for more than 140 seconds.
Not tainted 4.14.184-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D30096 4087 6357 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x8a6/0x1d70 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x5f0/0x1430 kernel/locking/mutex.c:893
ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x75a/0xfe0 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x7f/0xb0 fs/ioctl.c:692
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x45cba9
RSP: 002b:00007f27578a8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004e2240 RCX: 000000000045cba9
RDX: 000000000076006e RSI: 0000000040186f40 RDI: 0000000000000004
RBP: 000000000078c180 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000215 R14: 00000000004c472a R15: 00007f27578a96d4

Showing all locks held in the system:
1 lock held by khungtaskd/1058:
#0: (tasklist_lock){.+.+}, at: [<ffffffff8146c8d0>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
1 lock held by syz-executor.5/4061:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.4/4067:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.4/4080:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.4/4081:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.4/4094:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.3/4063:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.3/4070:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.3/4079:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.3/4083:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.3/4087:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.3/4089:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.1/4066:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.1/4078:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.1/4084:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.1/4085:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014
1 lock held by syz-executor.1/4086:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.2/4064:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.2/4075:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.0/4065:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe562>] ctrl_cdev_ioctl+0x142/0x220 drivers/mtd/ubi/cdev.c:1039
1 lock held by syz-executor.0/4068:
#0: (ubi_devices_mutex){+.+.}, at: [<ffffffff83cbe5b0>] ctrl_cdev_ioctl+0x190/0x220 drivers/mtd/ubi/cdev.c:1014

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

NMI backtrace for cpu 0
CPU: 0 PID: 1058 Comm: khungtaskd Not tainted 4.14.184-syzkaller #0
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+0x1b2/0x283 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x13a/0x17f lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5e2/0xb80 kernel/hung_task.c:274
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff863e461e


---
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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.