syzbot

INFO: task syz-executor.2:16196 blocked for more than 140 seconds.
      Not tainted 4.9.183+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.2  D25544 16196      1 0x00000004
 0000000000000087 ffff8801a318df00 ffff8801d338f380 ffff8801db721000
 ffff8801a9d697c0 ffff8801db721018 ffff8801b20e7538 ffffffff8280a5be
 1ffff1003641ce9d 0000000000000000 00ffffff830c2ee0 ffff8801db7218f0
Call Trace:
 [<0000000087f547cc>] schedule+0x92/0x1c0 kernel/sched/core.c:3546
 [<000000002df6141c>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3579
 [<000000005d584c7d>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<000000005d584c7d>] mutex_lock_nested+0x38d/0x920 kernel/locking/mutex.c:621
 [<00000000be0d1a1c>] loop_probe+0x76/0x180 drivers/block/loop.c:1953
 [<0000000044fe0efa>] kobj_lookup+0x221/0x410 drivers/base/map.c:124
 [<000000000b154ac5>] get_gendisk+0x3c/0x2d0 block/genhd.c:716
 [<000000002039e293>] __blkdev_get+0x356/0xeb0 fs/block_dev.c:1267
 [<00000000743c8eaf>] blkdev_get+0x2e8/0x920 fs/block_dev.c:1424
 [<00000000a4a111df>] blkdev_open+0x1aa/0x250 fs/block_dev.c:1579
 [<00000000a1ca7dbd>] do_dentry_open+0x422/0xd20 fs/open.c:772
 [<0000000071789df8>] vfs_open+0x105/0x230 fs/open.c:885
 [<0000000010b144f0>] do_last fs/namei.c:3457 [inline]
 [<0000000010b144f0>] path_openat+0xbf5/0x2f60 fs/namei.c:3581
 [<000000003141a407>] do_filp_open+0x1a1/0x280 fs/namei.c:3615
 [<00000000d5bcae4b>] do_sys_open+0x2f0/0x610 fs/open.c:1078
 [<00000000b7c453d3>] SYSC_open fs/open.c:1096 [inline]
 [<00000000b7c453d3>] SyS_open+0x2d/0x40 fs/open.c:1091
 [<000000003d2a9aad>] do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 [<00000000b78f1614>] 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: [<000000002348d663>] check_hung_uninterruptible_tasks kernel/hung_task.c:169 [inline]
 #0:  (rcu_read_lock){......}, at: [<000000002348d663>] watchdog+0x14b/0xaf0 kernel/hung_task.c:263
 #1:  (tasklist_lock){.+.+..}, at: [<000000009f9c0e57>] debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4336
3 locks held by rs:main Q:Reg/1928:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<000000000340174f>] __fdget_pos+0xa8/0xd0 fs/file.c:782
 #1:  (sb_writers#4){.+.+.+}, at: [<000000004ee8388f>] file_start_write include/linux/fs.h:2646 [inline]
 #1:  (sb_writers#4){.+.+.+}, at: [<000000004ee8388f>] vfs_write+0x3e9/0x520 fs/read_write.c:558
 #2:  (&sb->s_type->i_mutex_key#9){++++++}, at: [<00000000303d03e5>] inode_lock include/linux/fs.h:771 [inline]
 #2:  (&sb->s_type->i_mutex_key#9){++++++}, at: [<00000000303d03e5>] __generic_file_fsync+0xcd/0x1c0 fs/libfs.c:978
1 lock held by rsyslogd/1931:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<000000000340174f>] __fdget_pos+0xa8/0xd0 fs/file.c:782
2 locks held by getty/2058:
 #0:  (&tty->ldisc_sem){++++++}, at: [<00000000fe85b0f3>] ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:377
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<000000000913d33f>] n_tty_read+0x1fe/0x1820 drivers/tty/n_tty.c:2156
1 lock held by syz-executor.2/16196:
 #0:  (loop_index_mutex){+.+.+.}, at: [<00000000be0d1a1c>] loop_probe+0x76/0x180 drivers/block/loop.c:1953
2 locks held by syz-executor.5/27133:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<000000006c435f0c>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000009e3387e0>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621
2 locks held by syz-executor.1/24331:
 #0:  (loop_index_mutex){+.+.+.}, at: [<00000000c5bc7771>] loop_control_ioctl+0x7a/0x320 drivers/block/loop.c:1973
 #1:  (&lo->lo_ctl_mutex#2){+.+.+.}, at: [<0000000037bd0740>] loop_control_ioctl+0x17f/0x320 drivers/block/loop.c:1987
2 locks held by syz-executor.4/24327:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<00000000b1cfbd46>] lo_ioctl+0x8e/0x1b10 drivers/block/loop.c:1404
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<0000000084d76a77>] blkdev_reread_part+0x1f/0x40 block/ioctl.c:189
2 locks held by blkid/24336:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<000000006c435f0c>] __blkdev_get+0x10e/0xeb0 fs/block_dev.c:1273
 #1:  (loop_index_mutex){+.+.+.}, at: [<000000009e3387e0>] lo_open+0x1d/0xb0 drivers/block/loop.c:1621

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

NMI backtrace for cpu 1
CPU: 1 PID: 24 Comm: khungtaskd Not tainted 4.9.183+ #4
 ffff8801d98d7cc8 ffffffff81b580a1 0000000000000001 0000000000000000
 0000000000000001 ffffffff81099a01 dffffc0000000000 ffff8801d98d7d00
 ffffffff81b6333c 0000000000000001 0000000000000000 0000000000000001
Call Trace:
 [<0000000096a10357>] __dump_stack lib/dump_stack.c:15 [inline]
 [<0000000096a10357>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<00000000aa326d2e>] nmi_cpu_backtrace.cold+0x47/0x87 lib/nmi_backtrace.c:99
 [<00000000a1693143>] nmi_trigger_cpumask_backtrace+0x124/0x155 lib/nmi_backtrace.c:60
 [<0000000077ac50d5>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<00000000d3fa1293>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<00000000d3fa1293>] check_hung_task kernel/hung_task.c:126 [inline]
 [<00000000d3fa1293>] check_hung_uninterruptible_tasks kernel/hung_task.c:183 [inline]
 [<00000000d3fa1293>] watchdog+0x670/0xaf0 kernel/hung_task.c:263
 [<00000000015a7a0c>] kthread+0x278/0x310 kernel/kthread.c:211
 [<00000000a3b6ee30>] 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 0xffffffff82819711