kernel panic: hung_task: blocked tasks

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
3eb2ce825ea1ad89d20f7a3b5780df850e4be274 (Sun Mar 25 22:44:30 2018 +0000)
Linux 4.16-rc7
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=bca5bf3f416a9b06754d

So far this crash happened 3 times on upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6718502643695616
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8440362230543204781
compiler: gcc (GCC) 7.1.1 20170620
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org
penguin...@I-love.SAKURA.ne.jp vegard...@oracle.com]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bca5bf...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
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Kernel panic - not syncing: hung_task: blocked tasks
CPU: 0 PID: 869 Comm: khungtaskd Not tainted 4.16.0-rc7+ #3
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+0x194/0x24d lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
check_hung_task kernel/hung_task.c:133 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0x91d/0xd60 kernel/hung_task.c:249
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Dmitry Vyukov]

This now will be detected as corrupted:
https://github.com/google/syzkaller/commit/1b0214295f148c4543ebf55347784c02cf0b1c4a

#syz invalid

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