syzbot

INFO: task syz-executor3:15725 blocked for more than 120 seconds.
      Not tainted 4.9.78-g29eadc4 #20
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor3   D28144 15725   3407 0x00000004
 ffff8801d1ab0000 0000000000000000 ffff8801d0853480 ffff8801b2eb3000
 ffff8801db221b98 ffff8801c61576d0 ffffffff838a1bbb 0000000041b58ab3
 ffffffff84193238 00ffffff8123be20 ffff8801db222468 ffff8801db222490
Call Trace:
 [<ffffffff838a315f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3550
 [<ffffffff838af2bc>] schedule_timeout+0x56c/0x10b0 kernel/time/timer.c:1768
 [<ffffffff838a136e>] io_schedule_timeout+0x1be/0x390 kernel/sched/core.c:5172
 [<ffffffff838a4ace>] do_wait_for_common kernel/sched/completion.c:75 [inline]
 [<ffffffff838a4ace>] __wait_for_common kernel/sched/completion.c:93 [inline]
 [<ffffffff838a4ace>] wait_for_common_io kernel/sched/completion.c:107 [inline]
 [<ffffffff838a4ace>] wait_for_completion_io+0x20e/0x2e0 kernel/sched/completion.c:155
 [<ffffffff81cdac9b>] submit_bio_wait+0x11b/0x180 block/bio.c:885
 [<ffffffff81d0de47>] blkdev_issue_flush+0x157/0x220 block/blk-flush.c:518
 [<ffffffff81629fc5>] blkdev_fsync+0x85/0xb0 fs/block_dev.c:378
 [<ffffffff8161592a>] vfs_fsync_range+0x10a/0x250 fs/sync.c:195
 [<ffffffff81615a99>] vfs_fsync+0x29/0x30 fs/sync.c:209
 [<ffffffff824b24f3>] __loop_update_dio+0x453/0x5d0 drivers/block/loop.c:207
 [<ffffffff824b7462>] loop_set_dio drivers/block/loop.c:1323 [inline]
 [<ffffffff824b7462>] lo_ioctl+0x13a2/0x1990 drivers/block/loop.c:1377
 [<ffffffff81d374fa>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81d374fa>] blkdev_ioctl+0x4aa/0x1a60 block/ioctl.c:590
 [<ffffffff8162be8e>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815adfaa>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815adfaa>] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679
 [<ffffffff815aefcf>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815aefcf>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff838b2c6e>] entry_SYSCALL_64_fastpath+0x29/0xe8

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372df5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff81372df5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81237f80>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
2 locks held by getty/3309:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b0e32>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff820096f4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor3/15725:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b614f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
1 lock held by syz-executor3/15742:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b614f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
1 lock held by syz-executor3/15766:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b614f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337
1 lock held by syz-executor3/15768:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff824b614f>] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337

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

NMI backtrace for cpu 1
CPU: 1 PID: 514 Comm: khungtaskd Not tainted 4.9.78-g29eadc4 #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8af7d00 ffffffff81d943a9 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bac10 ffff8801d8af7d38
 ffffffff81d9f4cd 0000000000000001 0000000000000000 ffff8801d1ab6418
Call Trace:
 [<ffffffff81d943a9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d943a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9f4cd>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9f607>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bad04>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813733c0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813733c0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813733c0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813733c0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119a72d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b2fdc>] 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 0xffffffff838b18a6