syzbot

pktgen: kernel_thread() failed for cpu 0
pktgen: Cannot create thread for cpu 0 (-4)
pktgen: kernel_thread() failed for cpu 1
pktgen: Cannot create thread for cpu 1 (-4)
pktgen: Initialization failed for all threads
INFO: task loop4:9825 blocked for more than 120 seconds.
      Not tainted 4.9.96-g71fce1e #13
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
loop4           D28776  9825      2 0x00000000
 ffff8801d037e000 ffff8801cd3579c0 ffff8801cd3579c0 ffff8801cd2d6000
 ffff8801db221b98 ffff88019eb07490 ffffffff839e240d 1ffff10033d60e86
 ffffffff85342240 0000000041b58ab3 00ffffff841c08a0 ffff8801db222468
Call Trace:
 [<ffffffff839e3a0f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff839efe21>] schedule_timeout+0x861/0xf70 kernel/time/timer.c:1768
 [<ffffffff839e1bea>] io_schedule_timeout+0x1ba/0x390 kernel/sched/core.c:5180
 [<ffffffff839e4e59>] io_schedule include/linux/sched.h:460 [inline]
 [<ffffffff839e4e59>] bit_wait_io+0x19/0xa0 kernel/sched/wait.c:582
 [<ffffffff839e46fe>] __wait_on_bit_lock+0xce/0x1c0 kernel/sched/wait.c:421
 [<ffffffff839e4b98>] out_of_line_wait_on_bit_lock+0xe8/0x120 kernel/sched/wait.c:448
 [<ffffffff81626c2a>] wait_on_bit_lock_io include/linux/wait.h:1177 [inline]
 [<ffffffff81626c2a>] __lock_buffer fs/buffer.c:71 [inline]
 [<ffffffff81626c2a>] lock_buffer include/linux/buffer_head.h:359 [inline]
 [<ffffffff81626c2a>] block_read_full_page+0x6ba/0x8e0 fs/buffer.c:2303
 [<ffffffff8162d51c>] blkdev_readpage+0x1c/0x20 fs/block_dev.c:317
 [<ffffffff8143cd6a>] do_generic_file_read mm/filemap.c:1847 [inline]
 [<ffffffff8143cd6a>] generic_file_read_iter+0xc6a/0x1a90 mm/filemap.c:1971
 [<ffffffff8162fda5>] blkdev_read_iter+0x105/0x170 fs/block_dev.c:1738
 [<ffffffff8156dba7>] vfs_iter_read+0x297/0x3f0 fs/read_write.c:370
 [<ffffffff825cbd19>] lo_read_simple drivers/block/loop.c:345 [inline]
 [<ffffffff825cbd19>] do_req_filebacked drivers/block/loop.c:545 [inline]
 [<ffffffff825cbd19>] loop_handle_cmd drivers/block/loop.c:1698 [inline]
 [<ffffffff825cbd19>] loop_queue_work+0x14f9/0x2320 drivers/block/loop.c:1710
 [<ffffffff8119b139>] kthread_worker_fn+0x249/0x6b0 kernel/kthread.c:627
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f34dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373

Showing all locks held in the system:
2 locks held by khungtaskd/518:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813646ec>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423ce0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3778:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f14b2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8211c792>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor0/12116:
 #0:  (uuid_mutex){+.+.+.}, at: [<ffffffff81a968f7>] btrfs_open_devices+0x27/0xb0 fs/btrfs/volumes.c:1054

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

NMI backtrace for cpu 0
CPU: 0 PID: 518 Comm: khungtaskd Not tainted 4.9.96-g71fce1e #13
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8527d08 ffffffff81eb0b69 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d60 ffff8801d8527d40
 ffffffff81ebbe97 0000000000000000 0000000000000000 0000000000000003
Call Trace:
 [<ffffffff81eb0b69>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb0b69>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebbe97>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebbe2a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7e64>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364c84>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364c84>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364c84>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364c84>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ad5d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f34dc>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff839f1f16