linux-kernel - Re: [PATCH] oom: handle overflow in mem_cgroup_out_of

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Message-ID: <AANLkTikZwbmVr-jvOoyd0WZhfxtHvqK=n1B-zWLr3xDa@mail.gmail.com>
Date:	Wed, 26 Jan 2011 19:10:34 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] oom: handle overflow in mem_cgroup_out_of_memory()

On Wed, Jan 26, 2011 at 1:59 PM, Greg Thelen <gthelen@...gle.com> 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.
>

Why would the overflow occur? Due to the right shift being used with
unsigned long long? I am afraid I don't have quick access to a 32 bit
box to test the patch. May be I too drained to understand the problem,
can you post the corresponding assembly for analysis?

Balbir
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