From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx120.postini.com [74.125.245.120]) by kanga.kvack.org (Postfix) with SMTP id D88D66B004D for ; Wed, 29 Feb 2012 14:00:58 -0500 (EST) Date: Wed, 29 Feb 2012 20:00:46 +0100 From: Johannes Weiner Subject: Re: [PATCH 3.3] memcg: fix deadlock by inverting lrucare nesting Message-ID: <20120229190046.GC1673@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 , KAMEZAWA Hiroyuki , Konstantin Khlebnikov , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Tue, Feb 28, 2012 at 09:25:02PM -0800, Hugh Dickins wrote: > We have forgotten the rules of lock nesting: the irq-safe ones must be > taken inside the non-irq-safe ones, otherwise we are open to deadlock: > > CPU0 CPU1 > ---- ---- > lock(&(&pc->lock)->rlock); > local_irq_disable(); > lock(&(&zone->lru_lock)->rlock); > lock(&(&pc->lock)->rlock); > > lock(&(&zone->lru_lock)->rlock); > > To check a different locking issue, I happened to add a spin_lock to > memcg's bit_spin_lock in lock_page_cgroup(), and lockdep very quickly > complained about __mem_cgroup_commit_charge_lrucare() (on CPU1 above). > > So delete __mem_cgroup_commit_charge_lrucare(), passing a bool lrucare > to __mem_cgroup_commit_charge() instead, taking zone->lru_lock under > lock_page_cgroup() in the lrucare case. > > The original was using spin_lock_irqsave, but we'd be in more trouble > if it were ever called at interrupt time: unconditional _irq is enough. > And ClearPageLRU before del from lru, SetPageLRU before add to lru: no > strong reason, but that is the ordering used consistently elsewhere. > > Signed-off-by: Hugh Dickins Acked-by: Johannes Weiner -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org