From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932109AbaBDQGG (ORCPT ); Tue, 4 Feb 2014 11:06:06 -0500 Received: from zene.cmpxchg.org ([85.214.230.12]:57228 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754903AbaBDQGD (ORCPT ); Tue, 4 Feb 2014 11:06:03 -0500 Date: Tue, 4 Feb 2014 11:05:58 -0500 From: Johannes Weiner To: Michal Hocko Cc: Andrew Morton , KAMEZAWA Hiroyuki , KOSAKI Motohiro , LKML , linux-mm@kvack.org Subject: Re: [PATCH -v2 3/6] memcg: mm == NULL is not allowed for mem_cgroup_try_charge_mm Message-ID: <20140204160558.GO6963@cmpxchg.org> References: <1391520540-17436-1-git-send-email-mhocko@suse.cz> <1391520540-17436-4-git-send-email-mhocko@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1391520540-17436-4-git-send-email-mhocko@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 04, 2014 at 02:28:57PM +0100, Michal Hocko wrote: > An ancient comment tries to explain that a given mm might be NULL when a > task is migrated. It has been introduced by 8a9f3ccd (Memory controller: > memory accounting) along with other bigger changes so it is not much > more specific about the conditions. > > Anyway, Even if the task is migrated to another memcg there is no way we > can see NULL mm struct. So either this was not correct from the very > beginning or it is not true anymore. > The only remaining case would be seeing charges after exit_mm but that > would be a bug on its own as the task doesn't have an address space > anymore. > > This patch replaces the check by VM_BUG_ON to make it obvious that we > really expect non-NULL mm_struct. > > Signed-off-by: Michal Hocko Acked-by: Johannes Weiner