From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753196Ab1GTS0q (ORCPT ); Wed, 20 Jul 2011 14:26:46 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:33572 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753123Ab1GTS0n (ORCPT ); Wed, 20 Jul 2011 14:26:43 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, greearb@candelatech.com, edt@aei.ca, Peter Zijlstra , "Paul E. McKenney" Subject: [PATCH tip/core/urgent 6/7] softirq,rcu: Inform RCU of irq_exit() activity Date: Wed, 20 Jul 2011 11:26:22 -0700 Message-Id: <1311186383-24819-6-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20110720182512.GA22946@linux.vnet.ibm.com> References: <20110720182512.GA22946@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra The rcu_read_unlock_special() function relies on in_irq() to exclude scheduler activity from interrupt level. This fails because exit_irq() can invoke the scheduler after clearing the preempt_count() bits that in_irq() uses to determine that it is at interrupt level. This situation can result in failures as follows: $task IRQ SoftIRQ rcu_read_lock() /* do stuff */ |= UNLOCK_BLOCKED rcu_read_unlock() --t->rcu_read_lock_nesting irq_enter(); /* do stuff, don't use RCU */ irq_exit(); sub_preempt_count(IRQ_EXIT_OFFSET); invoke_softirq() ttwu(); spin_lock_irq(&pi->lock) rcu_read_lock(); /* do stuff */ rcu_read_unlock(); rcu_read_unlock_special() rcu_report_exp_rnp() ttwu() spin_lock_irq(&pi->lock) /* deadlock */ rcu_read_unlock_special(t); Ed can simply trigger this 'easy' because invoke_softirq() immediately does a ttwu() of ksoftirqd/# instead of doing the in-place softirq stuff first, but even without that the above happens. Cure this by also excluding softirqs from the rcu_read_unlock_special() handler and ensuring the force_irqthreads ksoftirqd/# wakeup is done from full softirq context. [ Alternatively, delaying the ->rcu_read_lock_nesting decrement until after the special handling would make the thing more robust in the face of interrupts as well. And there is a separate patch for that. ] Cc: Thomas Gleixner Reported-and-tested-by: Ed Tomlinson Signed-off-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 2 +- kernel/softirq.c | 12 ++++++++++-- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index d9d7a89..8aafbb8 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -318,7 +318,7 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) } /* Hardware IRQ handlers cannot block. */ - if (in_irq()) { + if (in_irq() || in_serving_softirq()) { local_irq_restore(flags); return; } diff --git a/kernel/softirq.c b/kernel/softirq.c index 40cf63d..fca82c3 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -315,16 +315,24 @@ static inline void invoke_softirq(void) { if (!force_irqthreads) __do_softirq(); - else + else { + __local_bh_disable((unsigned long)__builtin_return_address(0), + SOFTIRQ_OFFSET); wakeup_softirqd(); + __local_bh_enable(SOFTIRQ_OFFSET); + } } #else static inline void invoke_softirq(void) { if (!force_irqthreads) do_softirq(); - else + else { + __local_bh_disable((unsigned long)__builtin_return_address(0), + SOFTIRQ_OFFSET); wakeup_softirqd(); + __local_bh_enable(SOFTIRQ_OFFSET); + } } #endif -- 1.7.3.2