From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 98B946B0092 for ; Wed, 26 Jan 2011 12:33:29 -0500 (EST) From: Greg Thelen Subject: Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory() References: <1296030555-3594-1-git-send-email-gthelen@google.com> <20110126170713.GA2401@cmpxchg.org> Date: Wed, 26 Jan 2011 09:33:09 -0800 In-Reply-To: <20110126170713.GA2401@cmpxchg.org> (Johannes Weiner's message of "Wed, 26 Jan 2011 18:07:13 +0100") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org To: Johannes Weiner Cc: Andrew Morton , David Rientjes , KOSAKI Motohiro , Minchan Kim , KAMEZAWA Hiroyuki , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Johannes Weiner writes: > 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 I agree that min_t() is clearer. Does the following look better? Author: Greg Thelen Date: Wed Jan 26 00:05:59 2011 -0800 oom: handle truncation in mem_cgroup_out_of_memory() mem_cgroup_get_limit() returns a byte limit as an unsigned 64 bit value. mem_cgroup_out_of_memory() converts this byte limit to an unsigned long page count. Prior to this patch, the 32 bit version of mem_cgroup_out_of_memory() would silently truncate the most significant 20 bits from byte limit when constructing the limit as a page count. For byte limits with the lowest 44 bits set to zero, this truncation would compute a page limit of zero. This patch checks for such large byte limits that cannot be converted to page counts without loosing information. In such situations, where a 32 bit page counter is too small to represent the corresponding byte count, select a maximal page count. Signed-off-by: Greg Thelen diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 7dcca55..0164060 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_t(u64, mem_cgroup_get_limit(mem) >> PAGE_SHIFT, ULONG_MAX); read_lock(&tasklist_lock); retry: p = select_bad_process(&points, limit, mem, NULL); -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org