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

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Date:   Tue, 30 Apr 2019 17:07:53 +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 14:18:21, Al Viro wrote:
> On Tue, Apr 30, 2019 at 03:07:39PM +0200, Jan Kara wrote:
> > 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.
> 
> Not with the patch upthread.  lo_ioctl() part was
> 
> @@ -1567,10 +1564,9 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
>  	case LOOP_SET_BLOCK_SIZE:
>  		if (!(mode & FMODE_WRITE) && !capable(CAP_SYS_ADMIN))
>  			return -EPERM;
> -		/* Fall through */
> +		return lo_simple_ioctl(lo, cmd, arg);
>  	default:
> -		err = lo_simple_ioctl(lo, cmd, arg);
> -		break;
> +		return -EINVAL;
>  	}
>  
>  	return err;
> 
> so anything unrecognized doesn't make it to lo_simple_ioctl() at all.

Ah, right. I've missed that in your patch. So your patch should be really
fixing the problem. Will you post it officially? Thanks!

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