Re: [PATCH v3 10/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline
From: Michael Wang <hidden>
Date: 2013-07-02 05:33:17
Also in:
linux-arch, linux-pm, lkml, netdev
Hi, Srivatsa On 06/28/2013 03:54 AM, Srivatsa S. Bhat wrote: [snip]
quoted hunk ↗ jump to hunk
@@ -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
quoted hunk ↗ jump to hunk
* * 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);