linux-kernel - Re: INFO: task hung in __get

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Message-ID: <20190430130739.GA11224@quack2.suse.cz>
Date:   Tue, 30 Apr 2019 15:07:39 +0200
From:   Jan Kara <jack@...e.cz>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jan Kara <jack@...e.cz>,
        syzbot <syzbot+10007d66ca02b08f0e60@...kaller.appspotmail.com>,
        axboe@...nel.dk, dvyukov@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, penguin-kernel@...ove.sakura.ne.jp,
        syzkaller-bugs@...glegroups.com
Subject: Re: INFO: task hung in __get_super

On Tue 30-04-19 04:11:44, Al Viro wrote:
> On Tue, Apr 30, 2019 at 04:55:01AM +0200, Jan Kara wrote:
> 
> > Yeah, you're right. And if we push the patch a bit further to not take
> > loop_ctl_mutex for invalid ioctl number, that would fix the problem. I
> > can send a fix.
> 
> Huh?  We don't take it until in lo_simple_ioctl(), and that patch doesn't
> get to its call on invalid ioctl numbers.  What am I missing here?

Doesn't it? blkdev_ioctl() calls into __blkdev_driver_ioctl() for
unrecognized ioctl numbers. That calls into lo_ioctl() in case of a loop
device. lo_ioctl() calls into lo_simple_ioctl() for ioctl numbers it
doesn't recognize and lo_simple_ioctl() will lock loop_ctl_mutex as you
say.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR