From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: [PATCH v2 22/45] percpu_counter: Use get/put_online_cpus_atomic() to prevent CPU offline Date: Wed, 26 Jun 2013 01:59:43 +0530 Message-ID: <20130625202943.16593.52711.stgit@srivatsabhat.in.ibm.com> References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: tglx@linutronix.de, peterz@infradead.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com Cc: rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu, fweisbec@gmail.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Al Viro , Tejun Heo "Srivatsa S. Bhat" List-Id: linux-arch.vger.kernel.org Once stop_machine() is gone from the CPU offline path, we won't be able to depend on disabling preemption to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, while invoking from atomic context. Cc: Al Viro Cc: Tejun Heo Signed-off-by: Srivatsa S. Bhat --- lib/percpu_counter.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index ba6085d..f5e718d 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -98,6 +98,15 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) s64 ret; int cpu; + /* + * The calls to get/put_online_cpus_atomic() is strictly not + * necessary, since CPU hotplug is explicitly handled via the + * hotplug callback which synchronizes through fbc->lock. + * But we add them here anyway to make it easier for the debug + * code under CONFIG_DEBUG_HOTPLUG_CPU to validate the correctness + * of hotplug synchronization. + */ + get_online_cpus_atomic(); raw_spin_lock(&fbc->lock); ret = fbc->count; for_each_online_cpu(cpu) { @@ -105,6 +114,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) ret += *pcount; } raw_spin_unlock(&fbc->lock); + put_online_cpus_atomic(); return ret; } EXPORT_SYMBOL(__percpu_counter_sum); From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e28smtp04.in.ibm.com ([122.248.162.4]:59543 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753115Ab3FYUdJ (ORCPT ); Tue, 25 Jun 2013 16:33:09 -0400 Received: from /spool/local by e28smtp04.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 26 Jun 2013 01:56:52 +0530 From: "Srivatsa S. Bhat" Subject: [PATCH v2 22/45] percpu_counter: Use get/put_online_cpus_atomic() to prevent CPU offline Date: Wed, 26 Jun 2013 01:59:43 +0530 Message-ID: <20130625202943.16593.52711.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> References: <20130625202452.16593.22810.stgit@srivatsabhat.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: tglx@linutronix.de, peterz@infradead.org, tj@kernel.org, oleg@redhat.com, paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au, mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org, walken@google.com, vincent.guittot@linaro.org, laijs@cn.fujitsu.com Cc: rostedt@goodmis.org, wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com, sbw@mit.edu, fweisbec@gmail.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, linux-pm@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Al Viro "Srivatsa S. Bhat" Message-ID: <20130625202943.OHx2_n7hYtyATIC_vCyhHvYDGDWcOJx-jTU7HGV3sTI@z> Once stop_machine() is gone from the CPU offline path, we won't be able to depend on disabling preemption to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, while invoking from atomic context. Cc: Al Viro Cc: Tejun Heo Signed-off-by: Srivatsa S. Bhat --- lib/percpu_counter.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index ba6085d..f5e718d 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -98,6 +98,15 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) s64 ret; int cpu; + /* + * The calls to get/put_online_cpus_atomic() is strictly not + * necessary, since CPU hotplug is explicitly handled via the + * hotplug callback which synchronizes through fbc->lock. + * But we add them here anyway to make it easier for the debug + * code under CONFIG_DEBUG_HOTPLUG_CPU to validate the correctness + * of hotplug synchronization. + */ + get_online_cpus_atomic(); raw_spin_lock(&fbc->lock); ret = fbc->count; for_each_online_cpu(cpu) { @@ -105,6 +114,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) ret += *pcount; } raw_spin_unlock(&fbc->lock); + put_online_cpus_atomic(); return ret; } EXPORT_SYMBOL(__percpu_counter_sum);