From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752840Ab2DBG04 (ORCPT ); Mon, 2 Apr 2012 02:26:56 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:44884 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1750911Ab2DBG0z (ORCPT ); Mon, 2 Apr 2012 02:26:55 -0400 X-IronPort-AV: E=Sophos;i="4.75,355,1330876800"; d="scan'208";a="4671462" Message-ID: <4F7947EB.5040809@cn.fujitsu.com> Date: Mon, 02 Apr 2012 14:32:11 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Peter Zijlstra , Ingo Molnar , LKML Subject: Re: [PATCH] rcu: remove the context test in rcu_read_unlock_special() References: <4F741B98.2070709@cn.fujitsu.com> <20120329215613.GX2450@linux.vnet.ibm.com> In-Reply-To: <20120329215613.GX2450@linux.vnet.ibm.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/04/02 14:26:40, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/04/02 14:26:43, Serialize complete at 2012/04/02 14:26:43 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/30/2012 05:56 AM, Paul E. McKenney wrote: > On Thu, Mar 29, 2012 at 04:21:44PM +0800, Lai Jiangshan wrote: >> Because of commit#26861f and #10f39bb1b2, the context test in >> rcu_read_unlock_special() are not needed. >> >> commit#26861f and #10f39bb1b2 ensure ->rcu_read_unlock_special is zero >> after rcu_read_unlock(), which implies: >> >> if ->rcu_read_unlock_special is non-zero, the out-most RCU C.S. can >> be interrupted or can be preempted, such context is safe to >> call rcu_read_unlock_special(). > > In theory, I am very much in favor of this, but in practice we need to > put a WARN_ON_ONCE() in the "if" statement to be removed for a few years > first. If there are never any warnings (or, more likely, once such > warnings have been fixed for some time), then this patch below would be > eminently sensible. > Add BUG_ON() instead, how about it? Thanks, Lai diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 22ecea0..22e2ef1 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -571,12 +571,6 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) if (special & RCU_READ_UNLOCK_NEED_QS) rcu_preempt_cpu_qs(); - /* Hardware IRQ handlers cannot block. */ - if (in_irq() || in_serving_softirq()) { - local_irq_restore(flags); - return; - } - /* Clean up if blocked during RCU read-side critical section. */ if (special & RCU_READ_UNLOCK_BLOCKED) { t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index c023464..e90593e 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -210,6 +210,7 @@ static void rcu_preempt_note_context_switch(int cpu) raw_spin_unlock_irqrestore(&rnp->lock, flags); } else if (t->rcu_read_lock_nesting < 0 && t->rcu_read_unlock_special) { + WARN_ON_ONCE(t->rcu_read_lock_nesting != INT_MIN); /* * Complete exit from RCU read-side critical section on @@ -239,7 +240,10 @@ static void rcu_preempt_note_context_switch(int cpu) */ void __rcu_read_lock(void) { - current->rcu_read_lock_nesting++; + struct task_struct *t = current; + + BUG_ON(!t->rcu_read_lock_nesting && t->rcu_read_unlock_special); + t->rcu_read_lock_nesting++; barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ } EXPORT_SYMBOL_GPL(__rcu_read_lock); @@ -338,12 +342,6 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) rcu_preempt_qs(smp_processor_id()); } - /* Hardware IRQ handlers cannot block. */ - if (in_irq() || in_serving_softirq()) { - local_irq_restore(flags); - return; - } - /* Clean up if blocked during RCU read-side critical section. */ if (special & RCU_READ_UNLOCK_BLOCKED) { t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; @@ -439,6 +437,7 @@ void __rcu_read_unlock(void) rcu_read_unlock_special(t); barrier(); /* ->rcu_read_unlock_special load before assign */ t->rcu_read_lock_nesting = 0; + BUG_ON(t->rcu_read_unlock_special); } #ifdef CONFIG_PROVE_LOCKING { diff --git a/kernel/softirq.c b/kernel/softirq.c index 671f959..7074f97 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -318,12 +318,8 @@ static inline void invoke_softirq(void) #else do_softirq(); #endif - } else { - __local_bh_disable((unsigned long)__builtin_return_address(0), - SOFTIRQ_OFFSET); + } else wakeup_softirqd(); - __local_bh_enable(SOFTIRQ_OFFSET); - } } /*