From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753586Ab1AZRH1 (ORCPT ); Wed, 26 Jan 2011 12:07:27 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:54993 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751685Ab1AZRH0 (ORCPT ); Wed, 26 Jan 2011 12:07:26 -0500 Date: Wed, 26 Jan 2011 18:07:13 +0100 From: Johannes Weiner To: Greg Thelen Cc: Andrew Morton , David Rientjes , KOSAKI Motohiro , Minchan Kim , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory() Message-ID: <20110126170713.GA2401@cmpxchg.org> References: <1296030555-3594-1-git-send-email-gthelen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1296030555-3594-1-git-send-email-gthelen@google.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 26, 2011 at 12:29:15AM -0800, Greg Thelen wrote: > mem_cgroup_get_limit() returns a byte limit as a unsigned 64 bit value, > which is converted to a page count by mem_cgroup_out_of_memory(). Prior > to this patch the conversion could overflow on 32 bit platforms > yielding a limit of zero. Balbir: It can truncate, because the conversion shrinks the required bits of this 64-bit number by only PAGE_SHIFT (12). Trying to store the resulting up to 52 significant bits in a 32-bit integer will cut up to 20 significant bits off. > Signed-off-by: Greg Thelen > --- > mm/oom_kill.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 7dcca55..3fcac51 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -538,7 +538,7 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask) > struct task_struct *p; > > check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0, NULL); > - limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT; > + limit = min(mem_cgroup_get_limit(mem) >> PAGE_SHIFT, (u64)ULONG_MAX); I would much prefer using min_t(u64, ...). To make it really, really explicit that this is 64-bit arithmetic. But that is just me, no correctness issue. Acked-by: Johannes Weiner