From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752112Ab0CWK7K (ORCPT ); Tue, 23 Mar 2010 06:59:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46403 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751389Ab0CWK7I (ORCPT ); Tue, 23 Mar 2010 06:59:08 -0400 Date: Tue, 23 Mar 2010 11:57:07 +0100 From: Oleg Nesterov To: David Howells Cc: Andrew Morton , Alexey Dobriyan , "Eric W. Biederman" , Roland McGrath , linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm 3/3] proc: make task_sig() lockless Message-ID: <20100323105707.GA8634@redhat.com> References: <20100322184136.GA3967@redhat.com> <15829.1269333449@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <15829.1269333449@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/23, David Howells wrote: > > Oleg Nesterov wrote: > > > task_sig() doesn't need ->siglock. > > Except that the data returned might then be inconsistent because you don't > hold a lock as you read the various bits of it. Yes. From the changelog: Of course, this means we read pending/blocked/etc nonatomically, but I hope this is OK for fs/proc. But I don't think the returned data could be "really" inconsistent from the /bin/ps pov. Yes, it is possible that, say, some signal is seen as both pending and ignored without ->siglock. Or we can report user->sigpending != 0 while pending/shpending are empty. But this looks harmless to me. We never guaranteed /proc/pid/status can't report the "intermediate" state, and I don't think we can confuse the user-space. Do you agree? Or do you think this can make problems ? Oleg.