Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751846Ab0KYKAE (ORCPT ); Thu, 25 Nov 2010 05:00:04 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:40125 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750997Ab0KYKAB convert rfc822-to-8bit (ORCPT ); Thu, 25 Nov 2010 05:00:01 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Peter Zijlstra Subject: Re: rcu_read_lock/unlock protect find_task_by_vpid call in migrate_pages Cc: kosaki.motohiro@jp.fujitsu.com, Dave Jones , Linux Kernel , linux-mm@vger.kernel.org, Andrew Morton , tglx , Oleg Nesterov , "Paul E. McKenney" , Christoph Lameter In-Reply-To: <1290674541.2072.564.camel@laptop> References: <20101125095012.F446.A69D9226@jp.fujitsu.com> <1290674541.2072.564.camel@laptop> Message-Id: <20101125174751.F45C.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 25 Nov 2010 18:59:58 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2666 Lines: 93 > On Thu, 2010-11-25 at 09:50 +0900, KOSAKI Motohiro wrote: > > Hi > > > > > Signed-off-by: Dave Jones > > > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > > index 4a57f13..2f0f55b 100644 > > > --- a/mm/mempolicy.c > > > +++ b/mm/mempolicy.c > > > @@ -1308,6 +1308,7 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, > > > > > > /* Find the mm_struct */ > > > read_lock(&tasklist_lock); > > > + rcu_read_lock(); > > > task = pid ? find_task_by_vpid(pid) : current; > > > if (!task) { > > > read_unlock(&tasklist_lock); > > > @@ -1315,6 +1316,7 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, > > > goto out; > > > } > > > mm = get_task_mm(task); > > > + rcu_read_unlock(); > > > read_unlock(&tasklist_lock); > > > > > > err = -EINVAL; > > > > Thanks reporting. but mmotm seems already has the same patch. > > Another one,... again: > > > Do we still need the tasklist_lock in this case? > > Also, why is that think complaining, surely the tasklist_lock pins any > and all PID objects? (cc to Christoph and Oleg) Good spotting. As far as I understand, find_task_by_pid() did required tasklist_lock in old days. but It isn't now. So I think we can remove tasklist_lock from here. =========================================================================== >From 9de9f70f74e55d92b5e9057e22fc629405f63295 Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro Date: Thu, 16 Dec 2010 17:49:23 +0900 Subject: [PATCH] mempolicy: remove tasklist_lock from migrate_pages Today, tasklist_lock in migrate_pages doesn't protect anything. rcu_read_lock() provide enough protection from pid hash walk. Signed-off-by: KOSAKI Motohiro --- mm/mempolicy.c | 3 --- 1 files changed, 0 insertions(+), 3 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 11ff260..9064945 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -1308,16 +1308,13 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, /* Find the mm_struct */ rcu_read_lock(); - read_lock(&tasklist_lock); task = pid ? find_task_by_vpid(pid) : current; if (!task) { - read_unlock(&tasklist_lock); rcu_read_unlock(); err = -ESRCH; goto out; } mm = get_task_mm(task); - read_unlock(&tasklist_lock); rcu_read_unlock(); err = -EINVAL; -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/