From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755063AbaCJUje (ORCPT ); Mon, 10 Mar 2014 16:39:34 -0400 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:49444 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755042AbaCJUjb (ORCPT ); Mon, 10 Mar 2014 16:39:31 -0400 From: "Srivatsa S. Bhat" Subject: [PATCH v3 31/52] arm64, debug-monitors: Fix CPU hotplug callback registration To: paulus@samba.org, oleg@redhat.com, mingo@kernel.org, rjw@rjwysocki.net, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org Cc: 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, linux-arch@vger.kernel.org, linux-pm@vger.kernel.org, linuxppc-dev@ozlabs.org, srivatsa.bhat@linux.vnet.ibm.com, Catalin Marinas , Russell King , Ingo Molnar , linux-arm-kernel@lists.infradead.org, Will Deacon , "Srivatsa S. Bhat" Date: Tue, 11 Mar 2014 02:09:20 +0530 Message-ID: <20140310203919.10746.1234.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20140310203312.10746.310.stgit@srivatsabhat.in.ibm.com> References: <20140310203312.10746.310.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: 14031020-2000-0000-0000-0000101B3A23 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_notifier_register_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_notifier_register_done(); Fix the debug-monitors code in arm64 by using this latter form of callback registration. Cc: Catalin Marinas Cc: Russell King Cc: Ingo Molnar Cc: linux-arm-kernel@lists.infradead.org Acked-by: Will Deacon Signed-off-by: Srivatsa S. Bhat --- arch/arm64/kernel/debug-monitors.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index 636ba8b..c985531 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -155,12 +155,16 @@ static struct notifier_block os_lock_nb = { static int debug_monitors_init(void) { + cpu_notifier_register_begin(); + /* Clear the OS lock. */ smp_call_function(clear_os_lock, NULL, 1); clear_os_lock(NULL); /* Register hotplug handler. */ - register_cpu_notifier(&os_lock_nb); + __register_cpu_notifier(&os_lock_nb); + + cpu_notifier_register_done(); return 0; } postcore_initcall(debug_monitors_init);