From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx185.postini.com [74.125.245.185]) by kanga.kvack.org (Postfix) with SMTP id 377F86B006C for ; Sun, 10 Jun 2012 18:15:37 -0400 (EDT) Date: Mon, 11 Jun 2012 00:15:16 +0200 From: Johannes Weiner Subject: Re: [PATCH] memcg: fix use_hierarchy css_is_ancestor oops regression Message-ID: <20120610221516.GJ1761@cmpxchg.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Andrew Morton , Konstantin Khlebnikov , KAMEZAWA Hiroyuki , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Sun, Jun 10, 2012 at 11:54:47AM -0700, Hugh Dickins wrote: > If use_hierarchy is set, reclaim testing soon oopses in css_is_ancestor() > called from __mem_cgroup_same_or_subtree() called from page_referenced(): > when processes are exiting, it's easy for mm_match_cgroup() to pass along > a NULL memcg coming from a NULL mm->owner. > > Check for that in __mem_cgroup_same_or_subtree(). Return true or false? > False because we cannot know if it was in the hierarchy, but also false > because it's better not to count a reference from an exiting process. > > Signed-off-by: Hugh Dickins Looks like an older version of the patch that introduced it slipped into the tree, Konstantin noted this problem during review. The final version did match = memcg && __mem_cgroup_same_or_subtree(root, memcg); in the caller because of it. Do you think it would be cleaner this way, since this is also the place where that memcg is looked up, and so the "can return NULL" handling after mem_cgroup_from_task() would be in the same place? But either way, Acked-by: Johannes Weiner Thanks, Hugh! -- 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