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Date: Fri, 6 Apr 2018 08:59:05 -0700
From: Omar Sandoval <osandov@osandov.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        viro@zeniv.linux.org.uk, osandov@fb.com, dvyukov@google.com,
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        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        mingo@redhat.com, linux-fsdevel@vger.kernel.org, knikanth@suse.de
Subject: Re: INFO: task hung in lo_ioctl
Message-ID: <20180406155905.GA11697@vader>
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On Fri, Apr 06, 2018 at 05:43:43PM +0200, Peter Zijlstra wrote:
> On Fri, Apr 06, 2018 at 10:55:03PM +0900, Tetsuo Handa wrote:
> > Peter Zijlstra wrote:
> > > On Fri, Apr 06, 2018 at 09:04:18PM +0900, Tetsuo Handa wrote:
> > > > +	/* Temporary hack for handling lock imbalance. */
> > > > +	if (__mutex_owner(&lo->lo_ctl_mutex) == current)
> > > > +		mutex_unlock(&lo->lo_ctl_mutex);
> > > 
> > > ARGGH.. you didn't read the comment we put on that?
> > > 
> > 
> > Commit 5b52330bbfe63b33 ("audit: fix auditd/kernel connection state tracking")
> > is using __mutex_owner(). ;-)
> 
> That got removed and the warning added.

Seems easy enough to fix without resorting to __mutex_owner() (untested):


diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 264abaaff662..cee258d12a1e 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1300,12 +1300,13 @@ loop_get_status_old(struct loop_device *lo, struct loop_info __user *arg) {
 static int
 loop_get_status64(struct loop_device *lo, struct loop_info64 __user *arg) {
 	struct loop_info64 info64;
-	int err = 0;
+	int err;
 
-	if (!arg)
-		err = -EINVAL;
-	if (!err)
-		err = loop_get_status(lo, &info64);
+	if (!arg) {
+		mutex_unlock(&lo->lo_ctl_mutex);
+		return -EINVAL;
+	}
+	err = loop_get_status(lo, &info64);
 	if (!err && copy_to_user(arg, &info64, sizeof(info64)))
 		err = -EFAULT;
 

I'll test it and send it up when I get into the office.