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

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Date:   Sat, 10 Nov 2018 17:09:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     axboe@...nel.dk, Jan Kara <jack@...e.cz>
Cc:     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

>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>
---
 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