From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx196.postini.com [74.125.245.196]) by kanga.kvack.org (Postfix) with SMTP id 933FE6B002B for ; Fri, 7 Sep 2012 19:06:56 -0400 (EDT) Message-ID: <504A7E11.2010700@jp.fujitsu.com> Date: Fri, 07 Sep 2012 19:06:57 -0400 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [PATCH 5/5] mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() References: <1345480594-27032-1-git-send-email-mgorman@suse.de> <1345480594-27032-6-git-send-email-mgorman@suse.de> <000001394596bd69-2c16d7fb-71b5-4009-95cc-7068103b2bfd-000000@email.amazonses.com> <20120821072611.GC1657@suse.de> In-Reply-To: <20120821072611.GC1657@suse.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: mgorman@suse.de Cc: cl@linux.com, akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, davej@redhat.com, ben@decadent.org.uk, ak@linux.intel.com, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org > mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma() > > [cc9a6c87: cpuset: mm: reduce large amounts of memory barrier related damage > v3] introduced a potential memory corruption. shmem_alloc_page() uses a > pseudo vma and it has one significant unique combination, vma->vm_ops=NULL > and vma->policy->flags & MPOL_F_SHARED. > > get_vma_policy() does NOT increase a policy ref when vma->vm_ops=NULL and > mpol_cond_put() DOES decrease a policy ref when a policy has MPOL_F_SHARED. > Therefore, when a cpuset update race occurs, alloc_pages_vma() falls in 'goto > retry_cpuset' path, decrements the reference count and frees the policy > prematurely. > > Signed-off-by: KOSAKI Motohiro > Signed-off-by: Mel Gorman > --- > mm/mempolicy.c | 12 +++++++++++- > 1 files changed, 11 insertions(+), 1 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 45f9825..9842ef5 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1552,8 +1552,18 @@ struct mempolicy *get_vma_policy(struct task_struct *task, > addr); > if (vpol) > pol = vpol; > - } else if (vma->vm_policy) > + } else if (vma->vm_policy) { > pol = vma->vm_policy; > + > + /* > + * shmem_alloc_page() passes MPOL_F_SHARED policy with > + * a pseudo vma whose vma->vm_ops=NULL. Take a reference > + * count on these policies which will be dropped by > + * mpol_cond_put() later > + */ > + if (mpol_needs_cond_ref(pol)) > + mpol_get(pol); > + } Ok, looks sene change. thank you. Acked-by: KOSAKI Motohiro > } > if (!pol) > pol = &default_policy; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org