From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753936Ab3KPAYQ (ORCPT ); Fri, 15 Nov 2013 19:24:16 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:52515 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753701Ab3KPAXr (ORCPT ); Fri, 15 Nov 2013 19:23:47 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 11/16] rcu: Warn on allegedly impossible rcu_read_unlock_special() from irq Date: Fri, 15 Nov 2013 16:23:33 -0800 Message-Id: <1384561418-30575-11-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1384561418-30575-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20131116002316.GA29049@linux.vnet.ibm.com> <1384561418-30575-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13111600-3532-0000-0000-0000031122A0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Lai Jiangshan After commit #10f39bb1b2c1 (rcu: protect __rcu_read_unlock() against scheduler-using irq handlers), it is no longer possible to enter the main body of rcu_read_lock_special() from an NMI, interrupt, or softirq handler. In theory, this implies that the check for "in_irq() || in_serving_softirq()" must always fail, so that in theory this check could be removed entirely. In practice, this commit wraps this condition with a WARN_ON_ONCE(). If this warning never triggers, then the condition will be removed entirely. [ paulmck: And one way of triggering the WARN_ON() is if a scheduling clock interrupt occurs in an RCU read-side critical section, setting RCU_READ_UNLOCK_NEED_QS, which is handled by rcu_read_unlock_special(). Updated this commit to return if only that bit was set. ] Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney Merge with 14b8cc88f674 (rcu: Warn on allegedly impossible rcu_read_unlock_special() from irq) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 59a3a17a0c57..29335faf96e7 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -361,10 +361,14 @@ void rcu_read_unlock_special(struct task_struct *t) special = t->rcu_read_unlock_special; if (special & RCU_READ_UNLOCK_NEED_QS) { rcu_preempt_qs(smp_processor_id()); + if (!t->rcu_read_unlock_special) { + local_irq_restore(flags); + return; + } } - /* Hardware IRQ handlers cannot block. */ - if (in_irq() || in_serving_softirq()) { + /* Hardware IRQ handlers cannot block, complain if they get here. */ + if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) { local_irq_restore(flags); return; } -- 1.8.1.5