From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH] cpufreq: schedutil: Fix sugov_start versus sugov_update_shared race Date: Fri, 7 Jul 2017 08:55:09 +0530 Message-ID: <20170707032509.GC1523@vireshk-i7> References: <1499363600-10732-1-git-send-email-markivx@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pf0-f169.google.com ([209.85.192.169]:35896 "EHLO mail-pf0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753322AbdGGDZO (ORCPT ); Thu, 6 Jul 2017 23:25:14 -0400 Received: by mail-pf0-f169.google.com with SMTP id q86so10311146pfl.3 for ; Thu, 06 Jul 2017 20:25:14 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1499363600-10732-1-git-send-email-markivx@codeaurora.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Vikram Mulukutla Cc: rafael.j.wysocki@intel.com, juri.lelli@arm.com, skannan@codeaurora.org, linux-pm@vger.kernel.org On 06-07-17, 10:53, Vikram Mulukutla wrote: > With a shared policy in place, when one of the CPUs in the policy is > hotplugged out and then brought back online, sugov_stop and > sugov_start are called in order. > > sugov_stop removes utilization hooks for each CPU in the policy and > does nothing else in the for_each_cpu loop. sugov_start on the other > hand iterates through the CPUs in the policy and re-initializes the > per-cpu structure _and_ adds the utilization hook. This implies that > the scheduler is allowed to invoke a CPU's utilization update hook > when the rest of the per-cpu structures have yet to be re-inited. > > Apart from some strange values in tracepoints this doesn't cause a > problem, but if we do end up accessing a pointer from the per-cpu > sugov_cpu structure somewhere in the sugov_update_shared path, > we will likely see crashes since the memset for another CPU in the > policy is free to race with sugov_update_shared from the CPU that is > ready to go. So let's fix this now to first init all per-cpu > structures, and then add the per-cpu utilization update hooks all at > once. > > Signed-off-by: Vikram Mulukutla > --- > kernel/sched/cpufreq_schedutil.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index 076a2e3..29a3970 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -610,6 +610,11 @@ static int sugov_start(struct cpufreq_policy *policy) > sg_cpu->sg_policy = sg_policy; > sg_cpu->flags = SCHED_CPUFREQ_RT; > sg_cpu->iowait_boost_max = policy->cpuinfo.max_freq; > + } > + > + for_each_cpu(cpu, policy->cpus) { > + struct sugov_cpu *sg_cpu = &per_cpu(sugov_cpu, cpu); > + > cpufreq_add_update_util_hook(cpu, &sg_cpu->update_util, > policy_is_shared(policy) ? > sugov_update_shared : Acked-by: Viresh Kumar -- viresh