syzbot

EXT4-fs (loop0): feature flags set on rev 0 fs, running e2fsck is recommended
EXT4-fs (loop0): can't mount with journal_checksum, fs mounted w/o journal
INFO: task syz-executor465:7959 blocked for more than 140 seconds.
      Not tainted 4.14.243-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor465 D28584  7959   7958 0x00000004
Call Trace:
 context_switch kernel/sched/core.c:2808 [inline]
 __schedule+0x88b/0x1de0 kernel/sched/core.c:3384
 schedule+0x8d/0x1b0 kernel/sched/core.c:3428
 schedule_timeout+0x80a/0xe90 kernel/time/timer.c:1724
 do_wait_for_common kernel/sched/completion.c:91 [inline]
 __wait_for_common kernel/sched/completion.c:112 [inline]
 wait_for_common+0x272/0x430 kernel/sched/completion.c:123
 kthread_stop+0xce/0x640 kernel/kthread.c:555
 ext4_fill_super+0x6880/0xb290 fs/ext4/super.c:4561
 mount_bdev+0x2b3/0x360 fs/super.c:1134
 mount_fs+0x92/0x2a0 fs/super.c:1237
 vfs_kern_mount.part.0+0x5b/0x470 fs/namespace.c:1046
 vfs_kern_mount fs/namespace.c:1036 [inline]
 do_new_mount fs/namespace.c:2549 [inline]
 do_mount+0xe53/0x2a00 fs/namespace.c:2879
 SYSC_mount fs/namespace.c:3095 [inline]
 SyS_mount+0xa8/0x120 fs/namespace.c:3072
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x445b2a
RSP: 002b:00007ffda85bc928 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffda85bc980 RCX: 0000000000445b2a
RDX: 0000000020000000 RSI: 00000000200000c0 RDI: 00007ffda85bc940
RBP: 00007ffda85bc940 R08: 00007ffda85bc980 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000200003f8
R13: 0000000000000003 R14: 0000000000000004 R15: 0000000000000005

Showing all locks held in the system:
1 lock held by khungtaskd/1533:
 #0:  (tasklist_lock){.+.+}, at: [<ffffffff87012a3c>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
1 lock held by syz-executor465/7959:
 #0:  (&type->s_umount_key#25/1){+.+.}, at: [<ffffffff81874346>] alloc_super fs/super.c:251 [inline]
 #0:  (&type->s_umount_key#25/1){+.+.}, at: [<ffffffff81874346>] sget_userns+0x556/0xc10 fs/super.c:516

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

NMI backtrace for cpu 0
CPU: 0 PID: 1533 Comm: khungtaskd Not tainted 4.14.243-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x13a/0x180 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
 watchdog+0x5b9/0xb40 kernel/hung_task.c:274
 kthread+0x30d/0x420 kernel/kthread.c:232
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff8723275e