From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 02/11] sched, rcu: Make RCU use resched_cpu() Date: Tue, 17 Sep 2013 16:40:12 +0200 Message-ID: <20130917144012.GC29354@twins.programming.kicks-ass.net> References: <20130917082838.218329307@infradead.org> <20130917091143.449530904@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from merlin.infradead.org ([205.233.59.134]:49272 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752607Ab3IQOkb (ORCPT ); Tue, 17 Sep 2013 10:40:31 -0400 Content-Disposition: inline In-Reply-To: <20130917091143.449530904@infradead.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linus Torvalds , Ingo Molnar Cc: Andi Kleen , Peter Anvin , Mike Galbraith , Thomas Gleixner , Arjan van de Ven , Frederic Weisbecker , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Paul McKenney , Thomas Meyer Thomas Meyer reported a UP build fail, should be fixed. --- Subject: sched, rcu: Make RCU use resched_cpu() From: Peter Zijlstra Date: Tue Sep 17 09:30:55 CEST 2013 We're going to deprecate and remove set_need_resched() for it will do the wrong thing. Make an exception for RCU and allow it to use resched_cpu() which will do the right thing. Cc: Paul McKenney Signed-off-by: Peter Zijlstra --- kernel/rcutree.c | 15 ++++++++++++++- kernel/sched/core.c | 10 ++-------- 2 files changed, 16 insertions(+), 9 deletions(-) --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -898,6 +898,12 @@ static void print_other_cpu_stall(struct force_quiescent_state(rsp); /* Kick them all. */ } +/* + * This function really isn't for public consumption, but RCU is special in + * that context switches can allow the state machine to make progress. + */ +extern void resched_cpu(int cpu); + static void print_cpu_stall(struct rcu_state *rsp) { int cpu; @@ -927,7 +933,14 @@ static void print_cpu_stall(struct rcu_s 3 * rcu_jiffies_till_stall_check() + 3; raw_spin_unlock_irqrestore(&rnp->lock, flags); - set_need_resched(); /* kick ourselves to get things going. */ + /* + * Attempt to revive the RCU machinery by forcing a context switch. + * + * A context switch would normally allow the RCU state machine to make + * progress and it could be we're stuck in kernel space without context + * switches for an entirely unreasonable amount of time. + */ + resched_cpu(smp_processor_id()); } static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -513,12 +513,11 @@ static inline void init_hrtick(void) * might also involve a cross-CPU call to trigger the scheduler on * the target CPU. */ -#ifdef CONFIG_SMP void resched_task(struct task_struct *p) { int cpu; - assert_raw_spin_locked(&task_rq(p)->lock); + lockdep_assert_held(&task_rq(p)->lock); if (test_tsk_need_resched(p)) return; @@ -546,6 +545,7 @@ void resched_cpu(int cpu) raw_spin_unlock_irqrestore(&rq->lock, flags); } +#ifdef CONFIG_SMP #ifdef CONFIG_NO_HZ_COMMON /* * In the semi idle case, use the nearest busy cpu for migrating timers @@ -693,12 +693,6 @@ void sched_avg_update(struct rq *rq) } } -#else /* !CONFIG_SMP */ -void resched_task(struct task_struct *p) -{ - assert_raw_spin_locked(&task_rq(p)->lock); - set_tsk_need_resched(p); -} #endif /* CONFIG_SMP */ #if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \