From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751679AbaEESxq (ORCPT ); Mon, 5 May 2014 14:53:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23230 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751468AbaEESxp (ORCPT ); Mon, 5 May 2014 14:53:45 -0400 Date: Mon, 5 May 2014 20:53:08 +0200 From: Oleg Nesterov To: "Paul E. McKenney" Cc: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org Subject: [PATCH] signal: Simplify __lock_task_sighand() Message-ID: <20140505185308.GA17507@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140505164719.GA31758@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: > > On 05/05, Paul E. McKenney wrote: > > > > Does the patch below cover it? > > Yes, thanks. > > Acked-by: Oleg Nesterov 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 + * rcu_read_unlock comment header for details. + */ + preempt_disable(); + rcu_read_lock(); for (;;) { - /* - * Disable interrupts early to avoid deadlocks. - * See rcu_read_unlock comment header for details. - */ - local_irq_save(*flags); - rcu_read_lock(); sighand = rcu_dereference(tsk->sighand); - if (unlikely(sighand == NULL)) { - rcu_read_unlock(); - local_irq_restore(*flags); + if (unlikely(sighand == NULL)) break; - } - spin_lock(&sighand->siglock); - if (likely(sighand == tsk->sighand)) { - rcu_read_unlock(); + spin_lock_irqsave(&sighand->siglock, *flags); + if (likely(sighand == tsk->sighand)) break; - } - spin_unlock(&sighand->siglock); - rcu_read_unlock(); - local_irq_restore(*flags); + spin_unlock_irqrestore(&sighand->siglock, *flags); } + rcu_read_unlock(); + preempt_enable(); return sighand; } -- 1.5.5.1