From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756051AbaBEWRQ (ORCPT ); Wed, 5 Feb 2014 17:17:16 -0500 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:58737 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756017AbaBEWRJ (ORCPT ); Wed, 5 Feb 2014 17:17:09 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 40/51] octeon, watchdog: Fix CPU hotplug callback registration To: paulus@samba.org, oleg@redhat.com, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org Cc: mingo@kernel.org, paulmck@linux.vnet.ibm.com, tj@kernel.org, walken@google.com, ego@linux.vnet.ibm.com, linux@arm.linux.org.uk, linux-kernel@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com, Wim Van Sebroeck , linux-watchdog@vger.kernel.org, "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:41:44 +0530 Message-ID: <20140205221144.19080.47455.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14020522-7014-0000-0000-00000448B6A5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations). Instead, the correct and race-free way of performing the callback registration is: cpu_maps_update_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_maps_update_done(); Fix the watchdog code in octeon by using this latter form of callback registration. Cc: Wim Van Sebroeck Cc: linux-watchdog@vger.kernel.org Signed-off-by: Srivatsa S. Bhat --- drivers/watchdog/octeon-wdt-main.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/watchdog/octeon-wdt-main.c b/drivers/watchdog/octeon-wdt-main.c index 4612088..c991acf 100644 --- a/drivers/watchdog/octeon-wdt-main.c +++ b/drivers/watchdog/octeon-wdt-main.c @@ -708,10 +708,13 @@ static int __init octeon_wdt_init(void) cpumask_clear(&irq_enabled_cpus); + cpu_maps_update_begin(); for_each_online_cpu(cpu) octeon_wdt_setup_interrupt(cpu); - register_hotcpu_notifier(&octeon_wdt_cpu_notifier); + __register_hotcpu_notifier(&octeon_wdt_cpu_notifier); + cpu_maps_update_done(); + out: return ret; } @@ -725,7 +728,8 @@ static void __exit octeon_wdt_cleanup(void) misc_deregister(&octeon_wdt_miscdev); - unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier); + cpu_maps_update_begin(); + __unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier); for_each_online_cpu(cpu) { int core = cpu2core(cpu); @@ -734,6 +738,9 @@ static void __exit octeon_wdt_cleanup(void) /* Free the interrupt handler */ free_irq(OCTEON_IRQ_WDOG0 + core, octeon_wdt_poke_irq); } + + cpu_maps_update_done(); + /* * Disable the boot-bus memory, the code it points to is soon * to go missing.