syzbot

INFO: task syz-executor0:10383 blocked for more than 120 seconds.
      Not tainted 4.9.80-gb30d2b5 #28
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0   D29616 10383   3771 0x00000004
 ffff8801d8ea6000 0000000000000000 ffff8801c20e5500 ffff8801d9b73000
 ffff8801db321b98 ffff8801d868fa40 ffffffff838a23db 0000000000000002
 0000000041b58ab3 00ffffff8418ae44 ffff8801db322468 ffff8801db322490
Call Trace:
 [<ffffffff838a397f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff81d21ea4>] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75
 [<ffffffff81d2af5d>] blk_freeze_queue block/blk-mq.c:92 [inline]
 [<ffffffff81d2af5d>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101
 [<ffffffff824b79ef>] loop_switch drivers/block/loop.c:599 [inline]
 [<ffffffff824b79ef>] loop_change_fd drivers/block/loop.c:682 [inline]
 [<ffffffff824b79ef>] lo_ioctl+0xfdf/0x1990 drivers/block/loop.c:1343
 [<ffffffff81d37cba>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81d37cba>] blkdev_ioctl+0x4aa/0x1a60 block/ioctl.c:590
 [<ffffffff8162c5fe>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815ae71a>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815ae71a>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815af73f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815af73f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838b346e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/515:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372ed5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372ed5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81237fe0>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3670:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b1652>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82009fa4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/10383:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b6a9f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
1 lock held by syz-executor0/10395:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b6a9f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337

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

NMI backtrace for cpu 1
CPU: 1 PID: 515 Comm: khungtaskd Not tainted 4.9.80-gb30d2b5 #28
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d84dfd00 ffffffff81d94b69 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bac60 ffff8801d84dfd38
 ffffffff81d9fc8d 0000000000000001 0000000000000000 ffff8801d8ea4c18
Call Trace:
 [<ffffffff81d94b69>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d94b69>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9fc8d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9fdc7>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bad54>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813734a0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813734a0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813734a0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813734a0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a73d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b37dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:477
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff838b20c6