linux-kernel - Re: WARNING: locking bug in loop_control

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Message-ID: <20181112110200.GB7175@quack2.suse.cz>
Date:   Mon, 12 Nov 2018 12:02:00 +0100
From:   Jan Kara <jack@...e.cz>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     axboe@...nel.dk, Jan Kara <jack@...e.cz>,
        syzbot <syzbot+c0138741c2290fc5e63f@...kaller.appspotmail.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING: locking bug in loop_control_ioctl

On Sat 10-11-18 17:09:09, Tetsuo Handa wrote:
> From 4b9e5556fada37dff1eff13665a229b69e1f7dd8 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Sat, 10 Nov 2018 17:04:40 +0900
> Subject: [PATCH] loop: Fix double mutex_unlock(&loop_ctl_mutex) in loop_control_ioctl().
> 
> Commit 0a42e99b58a20883 ("loop: Get rid of loop_index_mutex") forgot to
> remove mutex_unlock(&loop_ctl_mutex) from loop_control_ioctl() when
> replacing loop_index_mutex with loop_ctl_mutex.
> 
> Reported-by: syzbot <syzbot+c0138741c2290fc5e63f@...kaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Jan Kara <jack@...e.cz>

Yeah, my bad. Thanks for fixing this. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  drivers/block/loop.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index bf6bc35..176ab1f 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2074,12 +2074,10 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
>  			break;
>  		if (lo->lo_state != Lo_unbound) {
>  			ret = -EBUSY;
> -			mutex_unlock(&loop_ctl_mutex);
>  			break;
>  		}
>  		if (atomic_read(&lo->lo_refcnt) > 0) {
>  			ret = -EBUSY;
> -			mutex_unlock(&loop_ctl_mutex);
>  			break;
>  		}
>  		lo->lo_disk->private_data = NULL;
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR