Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756151AbaBEWSj (ORCPT ); Wed, 5 Feb 2014 17:18:39 -0500 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:45853 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751500AbaBEWSe (ORCPT ); Wed, 5 Feb 2014 17:18:34 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 47/51] profile: 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, Al Viro , Mauro Carvalho Chehab , "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:43:10 +0530 Message-ID: <20140205221310.19080.72463.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: 14020522-3568-0000-0000-000004E58D1D 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 profile code by using this latter form of callback registration. Cc: Al Viro Cc: Mauro Carvalho Chehab Signed-off-by: Srivatsa S. Bhat --- kernel/profile.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/kernel/profile.c b/kernel/profile.c index 6631e1e..df27769 100644 --- a/kernel/profile.c +++ b/kernel/profile.c @@ -591,18 +591,28 @@ out_cleanup: int __ref create_proc_profile(void) /* false positive from hotcpu_notifier */ { struct proc_dir_entry *entry; + int err = 0; if (!prof_on) return 0; - if (create_hash_tables()) - return -ENOMEM; + + cpu_maps_update_begin(); + + if (create_hash_tables()) { + err = -ENOMEM; + goto out; + } + entry = proc_create("profile", S_IWUSR | S_IRUGO, NULL, &proc_profile_operations); if (!entry) - return 0; + goto out; proc_set_size(entry, (1 + prof_len) * sizeof(atomic_t)); - hotcpu_notifier(profile_cpu_callback, 0); - return 0; + __hotcpu_notifier(profile_cpu_callback, 0); + +out: + cpu_maps_update_done(); + return err; } module_init(create_proc_profile); #endif /* CONFIG_PROC_FS */ -- 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/