syzbot

INFO: task syz-executor385:3867 blocked for more than 120 seconds.
      Not tainted 4.9.109-ge1815b3 #49
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor385 D29768  3867   3866 0x00000000
 ffff8801d76f6000 ffff8801c720ea00 ffff8801d98f3480 ffff8801d75fb000
 ffff8801db321c18 ffff8801d6d5fb48 ffffffff839e8a8d ffff8801d76f68c8
 ffffed003aeded18 ffff8801d76f6000 00fffc0000000000 ffff8801db3224e8
Call Trace:
 [<ffffffff839ea08f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839eaa13>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3590
 [<ffffffff839eee96>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff839eee96>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
 [<ffffffff815b2b9c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2b9c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2b9c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3c1f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3c1f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9993>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/520:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136662c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425cb7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3772:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f7b32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211fce2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor385/3867:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
1 lock held by syz-executor385/3868:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
2 locks held by syz-executor385/3869:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
 #1:  (&lo->lo_ctl_mutex#2){+.+...}, at: [<ffffffff825ccf66>] loop_control_ioctl+0x186/0x300 drivers/block/loop.c:1920
2 locks held by syz-executor385/3870:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81e564ae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
1 lock held by syz-executor385/3871:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
2 locks held by syz-executor385/3872:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81e564ae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
2 locks held by syz-executor385/3873:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825ca87b>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344
 #1:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81e564ae>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:189
1 lock held by syz-executor385/3874:
 #0:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825cce5a>] loop_control_ioctl+0x7a/0x300 drivers/block/loop.c:1906
2 locks held by blkid/3876:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8163129c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825c591b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1555
2 locks held by blkid/3878:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8163129c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825c591b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1555
2 locks held by blkid/3883:
 #0:  (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff8163129c>] __blkdev_get+0x10c/0xd60 fs/block_dev.c:1268
 #1:  (loop_index_mutex){+.+.+.}, at: [<ffffffff825c591b>] lo_open+0x1b/0xa0 drivers/block/loop.c:1555

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

NMI backtrace for cpu 1
CPU: 1 PID: 520 Comm: khungtaskd Not tainted 4.9.109-ge1815b3 #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d92dfd08 ffffffff81eb3e29 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810b9580 ffff8801d92dfd40
 ffffffff81ebf127 0000000000000001 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb3e29>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3e29>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebf127>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebf0ba>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9684>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366bc4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366bc4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366bc4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366bc4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d04d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f9b5c>] 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 0xffffffff839f8596