syzbot

INFO: task syz-executor.4:2122 blocked for more than 140 seconds.
      Not tainted 4.9.171+ #49
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.4  D25480  2122      1 0x00000004
 ffff8801d7832f80 ffff8801d1bad800 ffff8801db721000 ffff8801d7e72f80
 ffff8801db721018 ffff8801a8e4fc48 ffffffff82801dde ffffffff810056bd
 ffffffff82812253 00ffffffffffffff ffff8801db7218f0 1ffff100351c9f78
Call Trace:
 [<00000000c3275599>] schedule+0x92/0x1c0 kernel/sched/core.c:3546
 [<00000000c89a60d1>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3579
 [<000000001c96e432>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<000000001c96e432>] mutex_lock_nested+0x38d/0x920 kernel/locking/mutex.c:621
 [<00000000c046e408>] blkdev_put+0x2b/0x560 fs/block_dev.c:1629
 [<000000009d2165a0>] blkdev_close+0x8b/0xb0 fs/block_dev.c:1678
 [<00000000cabf1a06>] __fput+0x274/0x720 fs/file_table.c:208
 [<00000000c0c6ed50>] ____fput+0x16/0x20 fs/file_table.c:244
 [<0000000046b4e5b4>] task_work_run+0x108/0x180 kernel/task_work.c:116
 [<00000000c146d49d>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<00000000c146d49d>] exit_to_usermode_loop+0x13b/0x160 arch/x86/entry/common.c:162
 [<000000007e8c808e>] prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 [<000000007e8c808e>] syscall_return_slowpath arch/x86/entry/common.c:263 [inline]
 [<000000007e8c808e>] do_syscall_64+0x3f7/0x570 arch/x86/entry/common.c:290
 [<000000006e8e8086>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/24:
 #0:  (rcu_read_lock){......}, at: [<000000004dc2fc3b>] check_hung_uninterruptible_tasks kernel/hung_task.c:169 [inline]
 #0:  (rcu_read_lock){......}, at: [<000000004dc2fc3b>] watchdog+0x14b/0xaf0 kernel/hung_task.c:263
 #1:  (tasklist_lock){.+.+..}, at: [<000000002001877a>] debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/1895:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<0000000078ca3500>] __fdget_pos+0xa8/0xd0 fs/file.c:782
2 locks held by getty/2025:
 #0:  (&tty->ldisc_sem){++++++}, at: [<00000000beec9e33>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:377
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<00000000de7a90ad>] n_tty_read+0x1fe/0x1820 drivers/tty/n_tty.c:2156
1 lock held by syz-executor.4/2122:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c046e408>] blkdev_put+0x2b/0x560 fs/block_dev.c:1629
2 locks held by syz-executor.3/2133:
 #0:  (loop_ctl_mutex/1){+.+.+.}, at: [<000000003bf0a07f>] lo_ioctl+0x85/0x1a10 drivers/block/loop.c:1405
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<0000000045fbe743>] blkdev_reread_part+0x1f/0x40 block/ioctl.c:189
1 lock held by syz-executor.1/7022:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
1 lock held by syz-executor.5/8267:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c046e408>] blkdev_put+0x2b/0x560 fs/block_dev.c:1629
1 lock held by syz-executor.0/8272:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c046e408>] blkdev_put+0x2b/0x560 fs/block_dev.c:1629
1 lock held by syz-executor.2/8275:
 #0:  (loop_ctl_mutex/1){+.+.+.}, at: [<000000003bf0a07f>] lo_ioctl+0x85/0x1a10 drivers/block/loop.c:1405
3 locks held by blkid/8273:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<000000003a3c71fd>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1587
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000001dfb7417>] lo_release+0x1e/0x1b0 drivers/block/loop.c:1664
 #2:  (loop_ctl_mutex#2){+.+.+.}, at: [<0000000066c86592>] __lo_release drivers/block/loop.c:1642 [inline]
 #2:  (loop_ctl_mutex#2){+.+.+.}, at: [<0000000066c86592>] lo_release+0x84/0x1b0 drivers/block/loop.c:1665
2 locks held by blkid/8279:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000aed5413e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1622
2 locks held by blkid/8280:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000aed5413e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1622
2 locks held by blkid/8281:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000aed5413e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1622
2 locks held by blkid/8285:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000aed5413e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1622
2 locks held by blkid/8286:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c2cef072>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000aed5413e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1622

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

NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: khungtaskd Not tainted 4.9.171+ #49
 ffff8801d98d7cc8 ffffffff81b4fb61 0000000000000001 0000000000000000
 0000000000000001 ffffffff81097501 dffffc0000000000 ffff8801d98d7d00
 ffffffff81b5adfc 0000000000000001 0000000000000000 0000000000000001
Call Trace:
 [<000000006cf9646b>] __dump_stack lib/dump_stack.c:15 [inline]
 [<000000006cf9646b>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<000000001298cc0a>] nmi_cpu_backtrace.cold+0x47/0x87 lib/nmi_backtrace.c:99
 [<00000000719c556b>] nmi_trigger_cpumask_backtrace+0x124/0x155 lib/nmi_backtrace.c:60
 [<00000000f000d372>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<0000000083fd4c52>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<0000000083fd4c52>] check_hung_task kernel/hung_task.c:126 [inline]
 [<0000000083fd4c52>] check_hung_uninterruptible_tasks kernel/hung_task.c:183 [inline]
 [<0000000083fd4c52>] watchdog+0x670/0xaf0 kernel/hung_task.c:263
 [<0000000002aa7bd4>] kthread+0x278/0x310 kernel/kthread.c:211
 [<00000000a061e804>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff82810e52