syzbot

INFO: task syz-executor068:2438 blocked for more than 140 seconds.
      Not tainted 4.9.194+ #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor068 D29096  2438   2435 0x00000000
 0000000000000083 ffff8801c80d97c0 ffff8801c858ac00 ffff8801db721000
 ffff8801c9775f00 ffff8801db721018 ffff8801c81d7688 ffffffff8281af8e
 ffff8801c80d97c0 ffffffff841f8b40 00ff8801c81d75e8 ffff8801db7218f0
Call Trace:
 [<000000000f0a2ed7>] schedule+0x92/0x1c0 kernel/sched/core.c:3546
 [<00000000f5acc27b>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3579
 [<00000000924350c3>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<00000000924350c3>] mutex_lock_nested+0x38d/0x920 kernel/locking/mutex.c:621
 [<000000001859d03e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621
 [<00000000b249d5d9>] __blkdev_get+0x268/0xeb0 fs/block_dev.c:1287
 [<0000000021ddb2ff>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1424
 [<00000000f7133286>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1579
 [<000000005c73c70a>] do_dentry_open+0x422/0xd20 fs/open.c:791
 [<00000000fcb80e78>] vfs_open+0x105/0x230 fs/open.c:904
 [<000000002356d63d>] do_last fs/namei.c:3541 [inline]
 [<000000002356d63d>] path_openat+0xbf5/0x2f60 fs/namei.c:3665
 [<000000003cf8e71c>] do_filp_open+0x1a1/0x280 fs/namei.c:3699
 [<00000000535f7b1a>] do_sys_open+0x2f0/0x610 fs/open.c:1097
 [<00000000563f4a14>] SYSC_open fs/open.c:1115 [inline]
 [<00000000563f4a14>] SyS_open+0x2d/0x40 fs/open.c:1110
 [<0000000043927aeb>] do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 [<000000004d3265b6>] 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: [<000000003c48beb4>] check_hung_uninterruptible_tasks kernel/hung_task.c:169 [inline]
 #0:  (rcu_read_lock){......}, at: [<000000003c48beb4>] watchdog+0x14b/0xaf0 kernel/hung_task.c:263
 #1:  (tasklist_lock){.+.+..}, at: [<000000006c930669>] debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/1897:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<00000000c430600a>] __fdget_pos+0xa8/0xd0 fs/file.c:782
2 locks held by getty/2025:
 #0:  (&tty->ldisc_sem){++++++}, at: [<00000000e099ab48>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<00000000201a1b54>] n_tty_read+0x1fe/0x1820 drivers/tty/n_tty.c:2156
2 locks held by syz-executor068/2438:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000001859d03e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621
1 lock held by syz-executor068/2469:
 #0:  (loop_index_mutex){+.+.+.}, at: [<000000005cca9fb3>] loop_control_ioctl+0x7a/0x320 drivers/block/loop.c:1973
2 locks held by syz-executor068/2472:
 #0:  (loop_index_mutex){+.+.+.}, at: [<000000005cca9fb3>] loop_control_ioctl+0x7a/0x320 drivers/block/loop.c:1973
 #1:  (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<000000005304b2bd>] loop_control_ioctl+0x17f/0x320 drivers/block/loop.c:1987
2 locks held by syz-executor068/2473:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<000000006ee9fa0d>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1587
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000d48edcc7>] lo_release+0x20/0x1b0 drivers/block/loop.c:1663
1 lock held by blkid/2475:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000c9323e6a>] blkdev_put+0x2b/0x560 fs/block_dev.c:1629
2 locks held by blkid/2476:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<000000006ee9fa0d>] __blkdev_put+0xbb/0x840 fs/block_dev.c:1587
 #1:  (loop_index_mutex){+.+.+.}, at: [<00000000d48edcc7>] lo_release+0x20/0x1b0 drivers/block/loop.c:1663
2 locks held by syz-executor068/2480:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000001859d03e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621
1 lock held by blkid/2482:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
1 lock held by blkid/2483:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
2 locks held by blkid/2484:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000001859d03e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621
2 locks held by syz-executor068/2485:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<00000000bfaf2b37>] lo_ioctl+0x8e/0x1b10 drivers/block/loop.c:1404
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<000000006b0b5cf4>] blkdev_reread_part+0x1f/0x40 block/ioctl.c:189
2 locks held by blkid/2487:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<00000000e6504f3f>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000001859d03e>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621

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

NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: khungtaskd Not tainted 4.9.194+ #0
 ffff8801d98d7cc8 ffffffff81b67001 0000000000000001 0000000000000000
 0000000000000001 ffffffff81099d01 dffffc0000000000 ffff8801d98d7d00
 ffffffff81b7229c 0000000000000001 0000000000000000 0000000000000001
Call Trace:
 [<000000006dae6b7e>] __dump_stack lib/dump_stack.c:15 [inline]
 [<000000006dae6b7e>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<00000000cd495e85>] nmi_cpu_backtrace.cold+0x47/0x87 lib/nmi_backtrace.c:99
 [<0000000024dda49f>] nmi_trigger_cpumask_backtrace+0x124/0x155 lib/nmi_backtrace.c:60
 [<00000000039273c7>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<000000007597b42d>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<000000007597b42d>] check_hung_task kernel/hung_task.c:126 [inline]
 [<000000007597b42d>] check_hung_uninterruptible_tasks kernel/hung_task.c:183 [inline]
 [<000000007597b42d>] watchdog+0x670/0xaf0 kernel/hung_task.c:263
 [<00000000ef32b2f2>] kthread+0x278/0x310 kernel/kthread.c:211
 [<00000000840713bf>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:375
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff8282a0e1