From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933158Ab0KQAlM (ORCPT ); Tue, 16 Nov 2010 19:41:12 -0500 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:50463 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932306Ab0KQAlK (ORCPT ); Tue, 16 Nov 2010 19:41:10 -0500 Date: Wed, 17 Nov 2010 09:24:01 +0900 From: Daisuke Nishimura To: Andrew Morton Cc: LKML , linux-mm , Balbir Singh , KAMEZAWA Hiroyuki , stable@kernel.org, Daisuke Nishimura Subject: Re: [BUGFIX] memcg: avoid deadlock between move charge and try_charge() Message-Id: <20101117092401.61c2117a.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20101116124117.64608b66.akpm@linux-foundation.org> References: <20101116191748.d6645376.nishimura@mxp.nes.nec.co.jp> <20101116124117.64608b66.akpm@linux-foundation.org> Organization: NEC Soft, Ltd. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 16 Nov 2010 12:41:17 -0800 Andrew Morton wrote: > On Tue, 16 Nov 2010 19:17:48 +0900 > Daisuke Nishimura wrote: > > > From: Daisuke Nishimura > > > > __mem_cgroup_try_charge() can be called under down_write(&mmap_sem)(e.g. > > mlock does it). This means it can cause deadlock if it races with move charge: > > > > Ex.1) > > move charge | try charge > > --------------------------------------+------------------------------ > > mem_cgroup_can_attach() | down_write(&mmap_sem) > > mc.moving_task = current | .. > > mem_cgroup_precharge_mc() | __mem_cgroup_try_charge() > > mem_cgroup_count_precharge() | prepare_to_wait() > > down_read(&mmap_sem) | if (mc.moving_task) > > -> cannot aquire the lock | -> true > > | schedule() > > > > Ex.2) > > move charge | try charge > > --------------------------------------+------------------------------ > > mem_cgroup_can_attach() | > > mc.moving_task = current | > > mem_cgroup_precharge_mc() | > > mem_cgroup_count_precharge() | > > down_read(&mmap_sem) | > > .. | > > up_read(&mmap_sem) | > > | down_write(&mmap_sem) > > mem_cgroup_move_task() | .. > > mem_cgroup_move_charge() | __mem_cgroup_try_charge() > > down_read(&mmap_sem) | prepare_to_wait() > > -> cannot aquire the lock | if (mc.moving_task) > > | -> true > > | schedule() > > > > To avoid this deadlock, we do all the move charge works (both can_attach() and > > attach()) under one mmap_sem section. > > And after this patch, we set/clear mc.moving_task outside mc.lock, because we > > use the lock only to check mc.from/to. > > > > Signed-off-by: Daisuke Nishimura > > I put this in the send-to-Linus-in-about-a-week queue. > > > Cc: > > The patch doesn't apply well to 2.6.36 so if we do want it backported > then please prepare a tested backport for the -stable guys? > O.K. I'll test a backported patch for 2.6.36.y and send it after this is merged into mainline. Thanks, Daisuke Nishimura.