syzbot

random: sshd: uninitialized urandom read (32 bytes read)
random: crng init done
INFO: task syz-executor122:3904 blocked for more than 140 seconds.
      Not tainted 4.9.112-g9e79039 #7
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor122 D27176  3904   3902 0x00000000
 ffff8801ba37b000 0000000000000000 ffff8801beae0fc0 ffffffff84629800
 ffff8801db221c18 ffff8801d70379f0 ffffffff839e907d 0000000000000002
 0000000041b58ab3 ffffffff843bb1d3 00ffffff81221570 ffff8801db2224e8
Call Trace:
 [<ffffffff839ea67f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3557
 [<ffffffff81e40944>] blk_mq_freeze_queue_wait+0x114/0x230 block/blk-mq.c:75
 [<ffffffff81e49c3d>] blk_freeze_queue block/blk-mq.c:92 [inline]
 [<ffffffff81e49c3d>] blk_mq_freeze_queue+0x1d/0x20 block/blk-mq.c:101
 [<ffffffff825ca462>] loop_switch drivers/block/loop.c:599 [inline]
 [<ffffffff825ca462>] loop_change_fd drivers/block/loop.c:685 [inline]
 [<ffffffff825ca462>] lo_ioctl+0x722/0x1aa0 drivers/block/loop.c:1350
 [<ffffffff81e56e46>] __blkdev_driver_ioctl block/ioctl.c:294 [inline]
 [<ffffffff81e56e46>] blkdev_ioctl+0x7b6/0x1a70 block/ioctl.c:590
 [<ffffffff81632cde>] block_ioctl+0xde/0x120 fs/block_dev.c:1688
 [<ffffffff815b2cec>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b2cec>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b2cec>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b3d6f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b3d6f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9f53>] 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: [<ffffffff8136675c>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136675c>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81425de7>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
2 locks held by getty/3779:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff839f8122>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8211edc2>] n_tty_read+0x202/0x16e0 drivers/tty/n_tty.c:2142
1 lock held by syz-executor122/3904:
 #0:  (&lo->lo_ctl_mutex/1){+.+.+.}, at: [<ffffffff825c9dcb>] lo_ioctl+0x8b/0x1aa0 drivers/block/loop.c:1344

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

NMI backtrace for cpu 0
CPU: 0 PID: 520 Comm: khungtaskd Not tainted 4.9.112-g9e79039 #7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8b67d08 ffffffff81eb3249 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b9bd0 ffff8801d8b67d40
 ffffffff81ebe547 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81eb3249>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eb3249>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81ebe547>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81ebe4da>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b9cd4>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81366cf4>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81366cf4>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81366cf4>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81366cf4>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119d0bd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839fa11c>] 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 0xffffffff839f8b86