Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754457AbaBEWLc (ORCPT ); Wed, 5 Feb 2014 17:11:32 -0500 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:46986 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753892AbaBEWL1 (ORCPT ); Wed, 5 Feb 2014 17:11:27 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 08/51] arm, hw-breakpoint: 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, Will Deacon , Russell King , linux-arm-kernel@lists.infradead.org, "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:36:04 +0530 Message-ID: <20140205220603.19080.80971.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: 14020522-5816-0000-0000-00000C1C6E53 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 hw-breakpoint code in arm by using this latter form of callback registration. Cc: Will Deacon Cc: Russell King Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Srivatsa S. Bhat --- arch/arm/kernel/hw_breakpoint.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index 3d44660..eaa7fcf 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -1072,6 +1072,8 @@ static int __init arch_hw_breakpoint_init(void) core_num_brps = get_num_brps(); core_num_wrps = get_num_wrps(); + cpu_maps_update_begin(); + /* * We need to tread carefully here because DBGSWENABLE may be * driven low on this core and there isn't an architected way to @@ -1088,6 +1090,7 @@ static int __init arch_hw_breakpoint_init(void) if (!cpumask_empty(&debug_err_mask)) { core_num_brps = 0; core_num_wrps = 0; + cpu_maps_update_done(); return 0; } @@ -1107,7 +1110,10 @@ static int __init arch_hw_breakpoint_init(void) TRAP_HWBKPT, "breakpoint debug exception"); /* Register hotplug and PM notifiers. */ - register_cpu_notifier(&dbg_reset_nb); + __register_cpu_notifier(&dbg_reset_nb); + + cpu_maps_update_done(); + pm_init(); return 0; } -- 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/