linux-kernel - WARNING: lock held when returning to user space!

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Date:   Fri, 06 Apr 2018 06:02:01 -0700
From:   syzbot <syzbot+31e8daa8b3fc129e75f2@...kaller.appspotmail.com>
To:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: WARNING: lock held when returning to user space!

Hello,

syzbot hit the following crash on upstream commit
38c23685b273cfb4ccf31a199feccce3bdcb5d83 (Fri Apr 6 04:29:35 2018 +0000)
Merge tag 'armsoc-drivers' of  
git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=31e8daa8b3fc129e75f2

So far this crash happened 9 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6407930337296384
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=4942413340606464
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=4764483918495744
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5813481738265533882
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+31e8daa8b3fc129e75f2@...kaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

================================================
WARNING: lock held when returning to user space!
4.16.0+ #3 Not tainted
------------------------------------------------
syzkaller433111/4462 is leaving the kernel with locks still held!
1 lock held by syzkaller433111/4462:
  #0: 0000000003a06fae (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x1ec0  
drivers/block/loop.c:1363

---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzkaller@...glegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is  
merged
into any tree, please reply to this email with:
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