INFO: task syz-executor7:7317 blocked for more than 120 seconds. Not tainted 4.9.79-g71f1469 #25 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor7 D28528 7317 4132 0x00000004 ffff8801cb09c800 ffff8801d6fb1500 ffff8801cbf80a80 ffff8801d90ab000 ffff8801db221b98 ffff8801ca57fa40 ffffffff838a23db 0000000000000002 0000000041b58ab3 00ffffff8418ae34 ffff8801db222468 ffff8801db222490 Call Trace: [] schedule+0x7f/0x1b0 kernel/sched/core.c:3550 [] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75 [] blk_freeze_queue block/blk-mq.c:92 [inline] [] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101 [] loop_switch drivers/block/loop.c:599 [inline] [] loop_change_fd drivers/block/loop.c:682 [inline] [] lo_ioctl+0xfdf/0x1990 drivers/block/loop.c:1343 [] __blkdev_driver_ioctl block/ioctl.c:294 [inline] [] blkdev_ioctl+0x4aa/0x1a60 block/ioctl.c:590 [] block_ioctl+0xde/0x120 fs/block_dev.c:1688 [] vfs_ioctl fs/ioctl.c:43 [inline] [] do_vfs_ioctl+0x1aa/0x1140 fs/ioctl.c:679 [] SYSC_ioctl fs/ioctl.c:694 [inline] [] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685 [] entry_SYSCALL_64_fastpath+0x29/0xe8 Showing all locks held in the system: 2 locks held by khungtaskd/514: #0: (rcu_read_lock){......}, at: [] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline] #0: (rcu_read_lock){......}, at: [] watchdog+0x125/0xa70 kernel/hung_task.c:239 #1: (tasklist_lock){.+.+..}, at: [] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336 2 locks held by getty/4046: #0: (&tty->ldisc_sem){++++++}, at: [] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367 #1: (&ldata->atomic_read_lock){+.+...}, at: [] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133 1 lock held by syz-executor7/7317: #0: (&lo->lo_ctl_mutex/1){+.+.+.}, at: [] lo_ioctl+0x8f/0x1990 drivers/block/loop.c:1337 ============================================= NMI backtrace for cpu 0 CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.79-g71f1469 #25 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 ffff8801d860fd00 ffffffff81d94829 0000000000000000 0000000000000000 0000000000000000 0000000000000001 ffffffff810bac60 ffff8801d860fd38 ffffffff81d9f94d 0000000000000000 0000000000000000 ffff8801cb864c18 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x128 lib/dump_stack.c:51 [] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99 [] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60 [] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37 [] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline] [] check_hung_task kernel/hung_task.c:125 [inline] [] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline] [] watchdog+0x6f0/0xa70 kernel/hung_task.c:239 [] kthread+0x26d/0x300 kernel/kthread.c:211 [] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:477 Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff838b20c6