From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753928AbcG0JI2 (ORCPT ); Wed, 27 Jul 2016 05:08:28 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:45474 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472AbcG0JIZ (ORCPT ); Wed, 27 Jul 2016 05:08:25 -0400 From: Richard Cochran To: Cc: , John Stultz , Jon Hunter , Linus Torvalds , Oleg Nesterov , Peter Zijlstra , Rasmus Villemoes , Sebastian Andrzej Siewior , Thomas Gleixner Subject: [PATCH] timers/core: Correct callback order during CPU hot plug. Date: Wed, 27 Jul 2016 11:08:18 +0200 Message-Id: <1469610498-25914-1-git-send-email-rcochran@linutronix.de> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <20160713153337.566790058@linutronix.de> References: <20160713153337.566790058@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On the tear-down path, the dead CPU callback for the timers was misplaced within the 'cpuhp_state' enumeration. There is a hidden dependency between the timers and block multiqueue. The timers callback must happen before the block multiqueue callback otherwise a RCU stall occurs. This patch fixes the order within the hot plug state machine. Signed-off-by: Richard Cochran Fixes: 24f73b99716a ("timers/core: Convert to hotplug state machine") Cc: John Stultz Cc: Jon Hunter Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rasmus Villemoes Cc: Sebastian Andrzej Siewior Cc: Thomas Gleixner Cc: rt@linutronix.de --- include/linux/cpuhotplug.h | 2 +- kernel/cpu.c | 15 ++++++++++----- 2 files changed, 11 insertions(+), 6 deletions(-) diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h index 6d405db..242bf53 100644 --- a/include/linux/cpuhotplug.h +++ b/include/linux/cpuhotplug.h @@ -20,9 +20,9 @@ enum cpuhp_state { CPUHP_PROFILE_PREPARE, CPUHP_X2APIC_PREPARE, CPUHP_SMPCFD_PREPARE, - CPUHP_TIMERS_DEAD, CPUHP_RCUTREE_PREP, CPUHP_NOTIFY_PREPARE, + CPUHP_TIMERS_DEAD, CPUHP_BRINGUP_CPU, CPUHP_AP_IDLE_DEAD, CPUHP_AP_OFFLINE, diff --git a/kernel/cpu.c b/kernel/cpu.c index 67f4943..ec12b72 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -1208,11 +1208,6 @@ static struct cpuhp_step cpuhp_bp_states[] = { .startup = smpcfd_prepare_cpu, .teardown = smpcfd_dead_cpu, }, - [CPUHP_TIMERS_DEAD] = { - .name = "timers dead", - .startup = NULL, - .teardown = timers_dead_cpu, - }, [CPUHP_RCUTREE_PREP] = { .name = "RCU-tree prepare", .startup = rcutree_prepare_cpu, @@ -1229,6 +1224,16 @@ static struct cpuhp_step cpuhp_bp_states[] = { .skip_onerr = true, .cant_stop = true, }, + /* + * On the tear-down path, timers_dead_cpu() must be invoked + * before blk_mq_queue_reinit_notify() from notify_dead(), + * otherwise a RCU stall occurs. + */ + [CPUHP_TIMERS_DEAD] = { + .name = "timers dead", + .startup = NULL, + .teardown = timers_dead_cpu, + }, /* Kicks the plugged cpu into life */ [CPUHP_BRINGUP_CPU] = { .name = "cpu:bringup", -- 2.1.4