linux-kernel - Re: [PATCH 4/5] mempolicy: fix refcount leak in mpol_set_shared

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Date:	Tue, 21 Aug 2012 08:15:32 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Andi Kleen <ak@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 4/5] mempolicy: fix refcount leak in
 mpol_set_shared_policy()

On Mon, Aug 20, 2012 at 07:46:09PM +0000, Christoph Lameter wrote:
> On Mon, 20 Aug 2012, Mel Gorman wrote:
> 
> > @@ -2318,9 +2323,7 @@ void mpol_free_shared_policy(struct shared_policy *p)
> >  	while (next) {
> >  		n = rb_entry(next, struct sp_node, nd);
> >  		next = rb_next(&n->nd);
> > -		rb_erase(&n->nd, &p->root);
> 
> Looks like we need to keep the above line? sp_delete does not remove the
> tree entry.
> 
> > -		mpol_put(n->policy);
> > -		kmem_cache_free(sn_cache, n);
> > +		sp_delete(p, n);

Yes it does, could you have accidentally mixed up sp_free (which does not
remove the tree entry) and sp_delete (which does)? The altered code ends
up looking like this;

static void sp_delete(struct shared_policy *sp, struct sp_node *n)
{
        pr_debug("deleting %lx-l%lx\n", n->start, n->end);
        rb_erase(&n->nd, &sp->root);				<----- frees node here
        sp_free(n);
}

void mpol_free_shared_policy(struct shared_policy *p)
{
        struct sp_node *n;
        struct rb_node *next;

        if (!p->root.rb_node)
                return;
        mutex_lock(&p->mutex);
        next = rb_first(&p->root);
        while (next) {
                n = rb_entry(next, struct sp_node, nd);
                next = rb_next(&n->nd);
                sp_delete(p, n);				<---- equivalent to rb_erase(&n->nd, &p->root); sp_free(n);
        }
        mutex_unlock(&p->mutex);
}

Thanks Christoph for looking at this.

-- 
Mel Gorman
SUSE Labs
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