Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965124Ab2EOCRV (ORCPT ); Mon, 14 May 2012 22:17:21 -0400 Received: from mail.windriver.com ([147.11.1.11]:49038 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964873Ab2EOCQM (ORCPT ); Mon, 14 May 2012 22:16:12 -0400 From: Paul Gortmaker To: , Subject: [34-longterm 016/179] rcu: Fix unpaired rcu_irq_enter() from locking selftests Date: Mon, 14 May 2012 22:11:52 -0400 Message-ID: <1337048075-6132-17-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.9.6 In-Reply-To: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> References: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2463 Lines: 65 From: Frederic Weisbecker ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit ba9f207c9f82115aba4ce04b22e0081af0ae300f upstream. HARDIRQ_ENTER() maps to irq_enter() which calls rcu_irq_enter(). But HARDIRQ_EXIT() maps to __irq_exit() which doesn't call rcu_irq_exit(). So for every locking selftest that simulates hardirq disabled, we create an imbalance in the rcu extended quiescent state internal state. As a result, after the first missing rcu_irq_exit(), subsequent irqs won't exit dyntick-idle mode after leaving the interrupt handler. This means that RCU won't see the affected CPU as being in an extended quiescent state, resulting in long grace-period delays (as in grace periods extending for hours). To fix this, just use __irq_enter() to simulate the hardirq context. This is sufficient for the locking selftests as we don't need to exit any extended quiescent state or perform any check that irqs normally do when they wake up from idle. As a side effect, this patch makes it possible to restore "rcu: Decrease memory-barrier usage based on semi-formal proof", which eventually helped finding this bug. Reported-and-tested-by: Yinghai Lu Signed-off-by: Frederic Weisbecker Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Paul E. McKenney Signed-off-by: Paul Gortmaker --- lib/locking-selftest.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c index 619313e..507a22f 100644 --- a/lib/locking-selftest.c +++ b/lib/locking-selftest.c @@ -144,7 +144,7 @@ static void init_shared_classes(void) #define HARDIRQ_ENTER() \ local_irq_disable(); \ - irq_enter(); \ + __irq_enter(); \ WARN_ON(!in_irq()); #define HARDIRQ_EXIT() \ -- 1.7.9.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/