From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp02.au.ibm.com (e23smtp02.au.ibm.com [202.81.31.144]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 581202C0846 for ; Tue, 11 Mar 2014 07:39:03 +1100 (EST) Received: from /spool/local by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 11 Mar 2014 06:39:03 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id F2AB32CE8051 for ; Tue, 11 Mar 2014 07:39:00 +1100 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s2AKclcq7799116 for ; Tue, 11 Mar 2014 07:38:47 +1100 Received: from d23av03.au.ibm.com (localhost [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s2AKcxK4021474 for ; Tue, 11 Mar 2014 07:39:00 +1100 From: "Srivatsa S. Bhat" Subject: [PATCH v3 28/52] x86, oprofile, nmi: 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 Date: Tue, 11 Mar 2014 02:08:49 +0530 Message-ID: <20140310203849.10746.36718.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> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Cc: linux-arch@vger.kernel.org, ego@linux.vnet.ibm.com, walken@google.com, linux@arm.linux.org.uk, linux-pm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, "Srivatsa S. Bhat" , "H. Peter Anvin" , tj@kernel.org, Robert Richter , Thomas Gleixner , paulmck@linux.vnet.ibm.com, Ingo Molnar List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 oprofile code in x86 by using this latter form of callback registration. But retain the calls to get/put_online_cpus(), since they are used in other places as well, to protect the variables 'nmi_enabled' and 'ctr_running'. Strictly speaking, this is not necessary since cpu_notifier_register_begin/done() provide a stronger synchronization with CPU hotplug than get/put_online_cpus(). However, let's retain the calls to get/put_online_cpus() to be consistent with the other call-sites. By nesting get/put_online_cpus() *inside* cpu_notifier_register_begin/done(), we avoid the ABBA deadlock possibility mentioned above. Cc: Robert Richter Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Signed-off-by: Srivatsa S. Bhat --- arch/x86/oprofile/nmi_int.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c index 6890d84..379e8bd 100644 --- a/arch/x86/oprofile/nmi_int.c +++ b/arch/x86/oprofile/nmi_int.c @@ -494,14 +494,19 @@ static int nmi_setup(void) if (err) goto fail; + cpu_notifier_register_begin(); + + /* Use get/put_online_cpus() to protect 'nmi_enabled' */ get_online_cpus(); - register_cpu_notifier(&oprofile_cpu_nb); nmi_enabled = 1; /* make nmi_enabled visible to the nmi handler: */ smp_mb(); on_each_cpu(nmi_cpu_setup, NULL, 1); + __register_cpu_notifier(&oprofile_cpu_nb); put_online_cpus(); + cpu_notifier_register_done(); + return 0; fail: free_msrs(); @@ -512,12 +517,18 @@ static void nmi_shutdown(void) { struct op_msrs *msrs; + cpu_notifier_register_begin(); + + /* Use get/put_online_cpus() to protect 'nmi_enabled' & 'ctr_running' */ get_online_cpus(); - unregister_cpu_notifier(&oprofile_cpu_nb); on_each_cpu(nmi_cpu_shutdown, NULL, 1); nmi_enabled = 0; ctr_running = 0; + __unregister_cpu_notifier(&oprofile_cpu_nb); put_online_cpus(); + + cpu_notifier_register_done(); + /* make variables visible to the nmi handler: */ smp_mb(); unregister_nmi_handler(NMI_LOCAL, "oprofile");