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)) (Client CN "e23smtp02.au.ibm.com", Issuer "GeoTrust SSL CA" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 6544B2C016F for ; Tue, 2 Jul 2013 15:33:15 +1000 (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, 2 Jul 2013 15:23:23 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp02.au.ibm.com (Postfix) with ESMTP id 6A3D72BB0056 for ; Tue, 2 Jul 2013 15:33:07 +1000 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r625Ww5i6226284 for ; Tue, 2 Jul 2013 15:32:58 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r625X5aA008804 for ; Tue, 2 Jul 2013 15:33:07 +1000 Message-ID: <51D2660A.8000401@linux.vnet.ibm.com> Date: Tue, 02 Jul 2013 13:32:58 +0800 From: Michael Wang MIME-Version: 1.0 To: "Srivatsa S. Bhat" Subject: Re: [PATCH v3 10/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline References: <20130627195136.29830.10445.stgit@srivatsabhat.in.ibm.com> <20130627195418.29830.34958.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20130627195418.29830.34958.stgit@srivatsabhat.in.ibm.com> Content-Type: text/plain; charset=UTF-8 Cc: peterz@infradead.org, fweisbec@gmail.com, Shaohua Li , linux-kernel@vger.kernel.org, Jan Beulich , walken@google.com, mingo@kernel.org, linux-arch@vger.kernel.org, vincent.guittot@linaro.org, xiaoguangrong@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org, rusty@rustcorp.com.au, rostedt@goodmis.org, namhyung@kernel.org, tglx@linutronix.de, Wang YanQing , laijs@cn.fujitsu.com, zhong@linux.vnet.ibm.com, netdev@vger.kernel.org, oleg@redhat.com, sbw@mit.edu, David.Laight@aculab.com, tj@kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, liguang List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi, Srivatsa On 06/28/2013 03:54 AM, Srivatsa S. Bhat wrote: [snip] > @@ -625,8 +632,9 @@ 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 protect against CPUs going > + * offline but not online. CPUs going online during the call will > + * not be seen or sent an IPI. I was a little confused about this comment, if the offline-cpu still have chances to become online, then there is chances that we will pick it from for_each_online_cpu(), isn't it? Did I miss some point? Regards, Michael Wang > * > * You must not call this function with disabled interrupts or > * from a hardware interrupt handler or from a bottom half handler. > @@ -641,26 +649,26 @@ 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); >