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Bhat" Subject: [PATCH v5 10/45] smp, cpu hotplug: Fix on_each_cpu_*() to prevent CPU offline properly 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 Date: Tue, 22 Jan 2013 13:05:17 +0530 Message-ID: <20130122073515.13822.80220.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> References: <20130122073210.13822.50434.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13012207-0260-0000-0000-0000026FFD81 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20130122_023722_923037_255B82F3 X-CRM114-Status: GOOD ( 15.43 ) X-Spam-Score: -1.9 (-) X-Spam-Report: SpamAssassin version 3.3.2 on merlin.infradead.org summary: Content analysis details: (-1.9 points) pts rule name description ---- ---------------------- -------------------------------------------------- -2.3 RCVD_IN_DNSWL_MED RBL: Sender listed at http://www.dnswl.org/, medium trust [202.81.31.140 listed in list.dnswl.org] 3.0 KHOP_BIG_TO_CC Sent to 10+ recipients instaed of Bcc or a list -0.7 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Cc: linux-arch@vger.kernel.org, linux@arm.linux.org.uk, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, fweisbec@gmail.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rostedt@goodmis.org, xiaoguangrong@linux.vnet.ibm.com, rjw@sisk.pl, sbw@mit.edu, wangyun@linux.vnet.ibm.com, srivatsa.bhat@linux.vnet.ibm.com, netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Once stop_machine() is gone from the CPU offline path, we won't be able to depend on preempt_disable() 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. Signed-off-by: Srivatsa S. Bhat --- kernel/smp.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index f421bcc..d870bfe 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -688,12 +688,12 @@ int on_each_cpu(void (*func) (void *info), void *info, int wait) unsigned long flags; int ret = 0; - preempt_disable(); + get_online_cpus_atomic(); ret = smp_call_function(func, info, wait); local_irq_save(flags); func(info); local_irq_restore(flags); - preempt_enable(); + put_online_cpus_atomic(); return ret; } EXPORT_SYMBOL(on_each_cpu); @@ -715,7 +715,11 @@ EXPORT_SYMBOL(on_each_cpu); void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait) { - int cpu = get_cpu(); + int cpu; + + get_online_cpus_atomic(); + + cpu = smp_processor_id(); smp_call_function_many(mask, func, info, wait); if (cpumask_test_cpu(cpu, mask)) { @@ -723,7 +727,7 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, func(info); local_irq_enable(); } - put_cpu(); + put_online_cpus_atomic(); } EXPORT_SYMBOL(on_each_cpu_mask); @@ -748,8 +752,9 @@ EXPORT_SYMBOL(on_each_cpu_mask); * The function might sleep if the GFP flags indicates a non * atomic allocation is allowed. * - * Preemption is disabled to protect against CPUs going offline but not online. - * CPUs going online during the call will not be seen or sent an IPI. + * We use get/put_online_cpus_atomic() to prevent CPUs from going + * offline in-between our operation. CPUs coming online during the + * call will not be seen or sent an IPI. * * You must not call this function with disabled interrupts or * from a hardware interrupt handler or from a bottom half handler. @@ -764,26 +769,26 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info), might_sleep_if(gfp_flags & __GFP_WAIT); if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) { - preempt_disable(); + get_online_cpus_atomic(); for_each_online_cpu(cpu) if (cond_func(cpu, info)) cpumask_set_cpu(cpu, cpus); on_each_cpu_mask(cpus, func, info, wait); - preempt_enable(); + put_online_cpus_atomic(); free_cpumask_var(cpus); } else { /* * No free cpumask, bother. No matter, we'll * just have to IPI them one by one. */ - preempt_disable(); + get_online_cpus_atomic(); for_each_online_cpu(cpu) if (cond_func(cpu, info)) { ret = smp_call_function_single(cpu, func, info, wait); WARN_ON_ONCE(!ret); } - preempt_enable(); + put_online_cpus_atomic(); } } EXPORT_SYMBOL(on_each_cpu_cond);