INFO: task hung in __blkdev_put

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 63d1657d ANDROID: sched/rt: fix the problem that rt_rq's u..
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=134f7d28c00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a8a239ffba5f9eef
dashboard link: https://syzkaller.appspot.com/bug?extid=801ee1539e8742f79a4c
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+801ee1...@syzkaller.appspotmail.com

INFO: task syz-executor0:9139 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D25640 9139 1 0x00000004
Call Trace:
schedule+0x92/0x1c0 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+0x559/0x1430 kernel/locking/mutex.c:893
__blkdev_put+0xb1/0x6d0 fs/block_dev.c:1778
blkdev_close+0x86/0xb0 fs/block_dev.c:1863
__fput+0x25e/0x700 fs/file_table.c:210
task_work_run+0x118/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x13b/0x160 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:267 [inline]
do_syscall_64+0x372/0x4b0 arch/x86/entry/common.c:294
INFO: task syz-executor3:11178 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3 D27224 11178 9189 0x80000002
Call Trace:
schedule+0x92/0x1c0 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+0x559/0x1430 kernel/locking/mutex.c:893
lo_release+0x19/0x170 drivers/block/loop.c:1643
__blkdev_put+0x518/0x6d0 fs/block_dev.c:1791
blkdev_close+0x86/0xb0 fs/block_dev.c:1863
__fput+0x25e/0x700 fs/file_table.c:210
task_work_run+0x118/0x190 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x903/0x2760 kernel/exit.c:865
INFO: task blkid:14070 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
blkid D28808 14070 2993 0x00000004
Call Trace:
schedule+0x92/0x1c0 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+0x559/0x1430 kernel/locking/mutex.c:893
lo_release+0x19/0x170 drivers/block/loop.c:1643
__blkdev_put+0x518/0x6d0 fs/block_dev.c:1791
blkdev_close+0x86/0xb0 fs/block_dev.c:1863
__fput+0x25e/0x700 fs/file_table.c:210
task_work_run+0x118/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x13b/0x160 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:267 [inline]
do_syscall_64+0x372/0x4b0 arch/x86/entry/common.c:294
INFO: task syz-executor3:14073 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3 D29192 14073 9189 0x00000004
Call Trace:
schedule+0x92/0x1c0 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+0x559/0x1430 kernel/locking/mutex.c:893
blkdev_reread_part+0x1b/0x40 block/ioctl.c:192
loop_reread_partitions+0x72/0x80 drivers/block/loop.c:614
loop_set_status+0xbff/0x11f0 drivers/block/loop.c:1183
INFO: task syz-executor3:14080 blocked for more than 140 seconds.
Not tainted 4.14.96+ #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3 D29152 14080 9189 0x00000004
Call Trace:
schedule+0x92/0x1c0 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+0x559/0x1430 kernel/locking/mutex.c:893
__blkdev_get+0xf3/0xf90 fs/block_dev.c:1457
blkdev_get+0x97/0x8b0 fs/block_dev.c:1612
blkdev_open+0x1cc/0x250 fs/block_dev.c:1770
do_dentry_open+0x41b/0xd60 fs/open.c:764
vfs_open+0x105/0x230 fs/open.c:878
do_last fs/namei.c:3455 [inline]
path_openat+0xb6b/0x2b70 fs/namei.c:3597
do_filp_open+0x1a1/0x280 fs/namei.c:3631
do_sys_open+0x2ca/0x590 fs/open.c:1071
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: (tasklist_lock){.+.+}, at: [<ffffffffa3fffeec>]
debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4541
2 locks held by getty/1767:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffffa4b36f02>]
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:275
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffffa4b32327>]
n_tty_read+0x1f7/0x1700 drivers/tty/n_tty.c:2156
1 lock held by syz-executor0/9139:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffffa4415361>]
__blkdev_put+0xb1/0x6d0 fs/block_dev.c:1778
2 locks held by syz-executor3/11178:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffffa4415361>]
__blkdev_put+0xb1/0x6d0 fs/block_dev.c:1778
#1: (loop_ctl_mutex){+.+.}, at: [<ffffffffa4be8669>]
lo_release+0x19/0x170 drivers/block/loop.c:1643
2 locks held by blkid/14070:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffffa4415361>]
__blkdev_put+0xb1/0x6d0 fs/block_dev.c:1778
#1: (loop_ctl_mutex){+.+.}, at: [<ffffffffa4be8669>]
lo_release+0x19/0x170 drivers/block/loop.c:1643
2 locks held by syz-executor3/14073:
#0: (loop_ctl_mutex/1){+.+.}, at: [<ffffffffa4be6c33>]
lo_ioctl+0x83/0x1970 drivers/block/loop.c:1404
#1: (&bdev->bd_mutex){+.+.}, at: [<ffffffffa4919d3b>]
blkdev_reread_part+0x1b/0x40 block/ioctl.c:192
1 lock held by syz-executor3/14080:
#0: (&bdev->bd_mutex){+.+.}, at: [<ffffffffa4415a73>]
__blkdev_get+0xf3/0xf90 fs/block_dev.c:1457

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

NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: khungtaskd Not tainted 4.14.96+ #20
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x10e lib/dump_stack.c:53
nmi_cpu_backtrace.cold+0x47/0x86 lib/nmi_backtrace.c:101
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffffa5650692


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[syzbot]

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