From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752362AbaEETzt (ORCPT ); Mon, 5 May 2014 15:55:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48806 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752198AbaEETzr (ORCPT ); Mon, 5 May 2014 15:55:47 -0400 Date: Mon, 5 May 2014 21:55:09 +0200 From: Oleg Nesterov To: "Paul E. McKenney" Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH] signal: Simplify __lock_task_sighand() Message-ID: <20140505195509.GA27674@redhat.com> References: <20140503161133.GA8838@redhat.com> <20140504180145.GC8754@linux.vnet.ibm.com> <20140504191757.GA11319@redhat.com> <20140504223804.GF8754@linux.vnet.ibm.com> <20140505132659.GA17996@redhat.com> <20140505152610.GK8754@linux.vnet.ibm.com> <20140505164719.GA31758@redhat.com> <20140505185308.GA17507@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140505185308.GA17507@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 05/05, Oleg Nesterov wrote: > > Yes, but please consider the cleanup below, on top of your change. > > This is subjective of course, but imho the code looks better without > the extra unlock/restore inside the loop. > > ------------------------------------------------------------------------------- > Subject: [PATCH] signal: Simplify __lock_task_sighand() > > __lock_task_sighand() does local_irq_save() to prevent the potential > deadlock, we can use preempt_disable() with the same effect. And in > this case we can do preempt_disable/enable + rcu_read_lock/unlock only > once outside of the main loop and simplify the code. Also shaves 112 > bytes from signal.o. > > Signed-off-by: Oleg Nesterov > --- > kernel/signal.c | 31 +++++++++++++------------------ > 1 files changed, 13 insertions(+), 18 deletions(-) > > diff --git a/kernel/signal.c b/kernel/signal.c > index 4368370..03a0fd4 100644 > --- a/kernel/signal.c > +++ b/kernel/signal.c > @@ -1260,30 +1260,25 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk, > unsigned long *flags) > { > struct sighand_struct *sighand; > - > + /* > + * We are going to do rcu_read_unlock() under spin_lock_irqsave(). > + * Make sure we can not be preempted after rcu_read_unlock(), see ^^^^^^^^^^^^^^^ Argh, typo in comment. I meant rcu_read_lock() of course. I'll send v2 tomorrow unless you dislike this change. Oleg.