Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756793AbYF1QQZ (ORCPT ); Sat, 28 Jun 2008 12:16:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752421AbYF1QQS (ORCPT ); Sat, 28 Jun 2008 12:16:18 -0400 Received: from x346.tv-sign.ru ([89.108.83.215]:43580 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750928AbYF1QQR (ORCPT ); Sat, 28 Jun 2008 12:16:17 -0400 Date: Sat, 28 Jun 2008 20:18:56 +0400 From: Oleg Nesterov To: Andrew Morton Cc: Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: [PATCH] migrate_timers: add comment, use spinlock_irq() Message-ID: <20080628161856.GA7030@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2187 Lines: 68 Add the comment to explain why the double lock in migrate_timers() can't deadlock. Change the code to use spinlock_irq() instead of local_irq_disable() + spin_lock(). Signed-off-by: Oleg Nesterov --- 26-rc2/kernel/timer.c~MIGRATE_TIMERS 2008-05-18 15:44:19.000000000 +0400 +++ 26-rc2/kernel/timer.c 2008-06-28 20:07:49.000000000 +0400 @@ -1443,9 +1443,11 @@ static void __cpuinit migrate_timers(int BUG_ON(cpu_online(cpu)); old_base = per_cpu(tvec_bases, cpu); new_base = get_cpu_var(tvec_bases); - - local_irq_disable(); - spin_lock(&new_base->lock); + /* + * The caller is globally serialized and nobody else + * takes two locks at once, deadlock is not possible. + */ + spin_lock_irq(&new_base->lock); spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); BUG_ON(old_base->running_timer); @@ -1460,8 +1462,7 @@ static void __cpuinit migrate_timers(int } spin_unlock(&old_base->lock); - spin_unlock(&new_base->lock); - local_irq_enable(); + spin_unlock_irq(&new_base->lock); put_cpu_var(tvec_bases); } #endif /* CONFIG_HOTPLUG_CPU */ --- 26-rc2/kernel/hrtimer.c~MIGRATE_TIMERS 2008-05-18 15:44:18.000000000 +0400 +++ 26-rc2/kernel/hrtimer.c 2008-06-28 20:08:15.000000000 +0400 @@ -1615,9 +1615,11 @@ static void migrate_hrtimers(int cpu) new_base = &get_cpu_var(hrtimer_bases); tick_cancel_sched_timer(cpu); - - local_irq_disable(); - spin_lock(&new_base->lock); + /* + * The caller is globally serialized and nobody else + * takes two locks at once, deadlock is not possible. + */ + spin_lock_irq(&new_base->lock); spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING); for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { @@ -1626,8 +1628,7 @@ static void migrate_hrtimers(int cpu) } spin_unlock(&old_base->lock); - spin_unlock(&new_base->lock); - local_irq_enable(); + spin_unlock_irq(&new_base->lock); put_cpu_var(hrtimer_bases); } #endif /* CONFIG_HOTPLUG_CPU */ -- 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/