Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932339AbaBEWSC (ORCPT ); Wed, 5 Feb 2014 17:18:02 -0500 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:58856 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753933AbaBEWR6 (ORCPT ); Wed, 5 Feb 2014 17:17:58 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 44/51] xen, balloon: 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, Konrad Rzeszutek Wilk , Boris Ostrovsky , David Vrabel , xen-devel@lists.xenproject.org, "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:42:32 +0530 Message-ID: <20140205221231.19080.66618.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: 14020522-9264-0000-0000-0000056591DD 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). Interestingly, the balloon code in xen can actually prevent double initialization and hence can use the following simplified form of callback registration: register_cpu_notifier(&foobar_cpu_notifier); get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); put_online_cpus(); A hotplug operation that occurs between registering the notifier and calling get_online_cpus(), won't disrupt anything, because the code takes care to perform the memory allocations only once. So reorganize the balloon code in xen this way to fix the deadlock with callback registration. Cc: Konrad Rzeszutek Wilk Cc: Boris Ostrovsky Cc: David Vrabel Cc: xen-devel@lists.xenproject.org Signed-off-by: Srivatsa S. Bhat --- drivers/xen/balloon.c | 35 +++++++++++++++++++++++------------ 1 file changed, 23 insertions(+), 12 deletions(-) diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 37d06ea..afe1a3f 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -592,19 +592,29 @@ static void __init balloon_add_region(unsigned long start_pfn, } } +static int alloc_balloon_scratch_page(int cpu) +{ + if (per_cpu(balloon_scratch_page, cpu) != NULL) + return 0; + + per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL); + if (per_cpu(balloon_scratch_page, cpu) == NULL) { + pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu); + return -ENOMEM; + } + + return 0; +} + + static int balloon_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { int cpu = (long)hcpu; switch (action) { case CPU_UP_PREPARE: - if (per_cpu(balloon_scratch_page, cpu) != NULL) - break; - per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL); - if (per_cpu(balloon_scratch_page, cpu) == NULL) { - pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu); + if (alloc_balloon_scratch_page(cpu)) return NOTIFY_BAD; - } break; default: break; @@ -624,15 +634,16 @@ static int __init balloon_init(void) return -ENODEV; if (!xen_feature(XENFEAT_auto_translated_physmap)) { - for_each_online_cpu(cpu) - { - per_cpu(balloon_scratch_page, cpu) = alloc_page(GFP_KERNEL); - if (per_cpu(balloon_scratch_page, cpu) == NULL) { - pr_warn("Failed to allocate balloon_scratch_page for cpu %d\n", cpu); + register_cpu_notifier(&balloon_cpu_notifier); + + get_online_cpus(); + for_each_online_cpu(cpu) { + if (alloc_balloon_scratch_page(cpu)) { + put_online_cpus(); return -ENOMEM; } } - register_cpu_notifier(&balloon_cpu_notifier); + put_online_cpus(); } pr_info("Initialising balloon driver\n"); -- 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/