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

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Date:   Fri, 6 Apr 2018 08:27:06 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     syzbot <syzbot+31e8daa8b3fc129e75f2@...kaller.appspotmail.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Omar Sandoval <osandov@...ndov.com>
Subject: Re: WARNING: lock held when returning to user space!

On 4/6/18 7:02 AM, syzbot wrote:
> 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

Is this a new regression? Omar did just fiddle with the locking a bit,
seems suspicious.

-- 
Jens Axboe