From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 6F4168D003B for ; Tue, 19 Apr 2011 21:50:58 -0400 (EDT) Received: from m3.gw.fujitsu.co.jp (unknown [10.0.50.73]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id D42BE3EE0C5 for ; Wed, 20 Apr 2011 10:50:52 +0900 (JST) Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id B2A6245DE94 for ; Wed, 20 Apr 2011 10:50:52 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 9471045DE93 for ; Wed, 20 Apr 2011 10:50:52 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 817FDE08003 for ; Wed, 20 Apr 2011 10:50:52 +0900 (JST) Received: from m107.s.css.fujitsu.com (m107.s.css.fujitsu.com [10.240.81.147]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 47F291DB803B for ; Wed, 20 Apr 2011 10:50:52 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH 1/2] break out page allocation warning code In-Reply-To: <1303263673.5076.612.camel@nimitz> References: <1303263673.5076.612.camel@nimitz> Message-Id: <20110420105059.460C.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Wed, 20 Apr 2011 10:50:51 +0900 (JST) Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: kosaki.motohiro@jp.fujitsu.com, David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Michal Nazarewicz , Andrew Morton , John Stultz Hi (Cc to John Stultz who/proc//comm author. I think we need to hear his opinion) > On Tue, 2011-04-19 at 14:21 -0700, David Rientjes wrote: > > On Tue, 19 Apr 2011, KOSAKI Motohiro wrote: > > > The rule is, > > > > > > 1) writing comm > > > need task_lock > > > 2) read _another_ thread's comm > > > need task_lock > > > 3) read own comm > > > no need task_lock > > > > That was true a while ago, but you now need to protect every thread's > > ->comm with get_task_comm() or ensuring task_lock() is held to protect > > against /proc/pid/comm which can change other thread's ->comm. That was > > different before when prctl(PR_SET_NAME) would only operate on current, so > > no lock was needed when reading current->comm. > > Everybody still goes through set_task_comm() to _set_ it, though. That > means that the worst case scenario that we get is output truncated > (possibly to nothing). We already have at least one existing user in > mm/ (kmemleak) that thinks this is OK. I'd tend to err in the direction > of taking a truncated or empty task name to possibly locking up the > system. > > There are also plenty of instances of current->comm going in to the > kernel these days. I count 18 added since 2.6.37. > > As for a long-term fix, locks probably aren't the answer. Would > something like this completely untested patch work? It would have the > added bonus that it keeps tsk->comm users working for the moment. We > could eventually add an rcu_read_lock()-annotated access function. The concept is ok to me. but AFAIK some caller are now using ARRAY_SIZE(tsk->comm). or sizeof(tsk->comm). Probably callers need to be changed too. Thanks. -- 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