From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030727AbXCSWer (ORCPT ); Mon, 19 Mar 2007 18:34:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965371AbXCSWer (ORCPT ); Mon, 19 Mar 2007 18:34:47 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:50888 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965145AbXCSWeq (ORCPT ); Mon, 19 Mar 2007 18:34:46 -0400 X-AuthUser: davidel@xmailserver.org Date: Mon, 19 Mar 2007 15:33:25 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Oleg Nesterov cc: "Eric W. Biederman" , Linux Kernel Mailing List , Andrew Morton , Linus Torvalds Subject: Re: [patch 2/13] signal/timer/event fds v6 - signalfd core ... In-Reply-To: <20070319203615.GA83@tv-sign.ru> Message-ID: References: <20070319203615.GA83@tv-sign.ru> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 Mar 2007, Oleg Nesterov wrote: > On 03/19, Davide Libenzi wrote: > > > > On Mon, 19 Mar 2007, Eric W. Biederman wrote: > > > > > > +struct signalfd_ctx { > > > > + struct list_head lnk; > > > > + wait_queue_head_t wqh; > > > > + sigset_t sigmask; > > > > + struct task_struct *tsk; > > > > +}; > > > > > > I think you want to use a struct pid *pid instead of a pointer to the > > > task struct here. It is slightly less efficient (one more > > > dereference) but it means that we won't pin the task struct in memory > > > indefinitely. Pinning the task_struct like this makes for a very > > > interesting way to get around the limits on the number of processes a > > > user can have. > > > > Hmm, when the task is detached from the sighand, we get a notify, so I > > could do a put from there. This would avoid the extra de-reference. I need > > to verify locking though ... > > In that case (if I understand you correctly) we don't need {get,put}_task_struct() > at all. > > signalfd_deliver(-1) sets ctx->tsk = NULL, signalfd_get_sighand() reads ->tsk > under rcu_read_lock(). The code becomes even simpler, we don't need to check > list_empty(&ctx->lnk). I'd need a get_task_struct in any case in order to safely call unlock_task_sighand(). At that point I'd prefer to just pass through the struct pid*. I'll be posting the new version for review as soon as I complete a few tests ... - Davide