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authorVikram Mulukutla <markivx@codeaurora.org>2017-07-06 10:53:20 -0700
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2017-07-12 14:47:48 +0200
commitab2f7cf141aa6734c4ca7525132d8cc236efee77 (patch)
tree6a2e41128c88d4843b795f566c69c3d572708871 /kernel
parent6f7da290413ba713f0cdd9ff1a2a9bb129ef4f6c (diff)
downloadlinux-ab2f7cf141aa6734c4ca7525132d8cc236efee77.tar.bz2
cpufreq: schedutil: Fix sugov_start() versus sugov_update_shared() race
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 <markivx@codeaurora.org> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/cpufreq_schedutil.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 076a2e31951c..29a397067ffa 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 :