linux-kernel - Re: [PATCH][v3.2 stable tree] dcache: Balance rcu_read_lock in have

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Message-ID: <1424044997.23608.21.camel@decadent.org.uk>
Date:	Mon, 16 Feb 2015 00:03:17 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH][v3.2 stable tree] dcache: Balance rcu_read_lock in
 have_submounts()

On Thu, 2015-02-12 at 00:28 -0500, Steven Rostedt wrote:
> On Wed, 11 Feb 2015 03:15:37 +0000
> Ben Hutchings <ben@...adent.org.uk> wrote:
> 
> > I've reviewed locking contexts in all three functions that I changed
> > when backporting "deal with deadlock in d_walk()".  It's actually worse
> > than you say:
> > 
> > - We don't hold this_parent->d_lock at the 'positive' label in
> > have_submounts(), but it is unlocked after 'rename_retry'.
> > - There is an rcu_read_unlock() after the 'out' label in
> > select_parent(), but it's not held at the 'goto out'.
> > 
> > Does the following patch work for you?
> 
> I booted the original 3.2 kernel 3 times and it succeeded once, and
> crashed the other two.
> 
> I applied this patch and booted it 5 times, and it succeeded every time.
> 
> I removed the patch, and it crashed on the very next boot.
> 
> Thus, I'd say it seems to have fixed the issue for me.
> 
> Tested-by: Steven Rostedt <rostedt@...dmis.org>
[...]

Thanks.

Ben.

-- 
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.

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