From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: [PATCH 3/3] cpufreq: Prevent problems in update_policy_cpu() if last_cpu == new_cpu Date: Thu, 12 Sep 2013 01:43:42 +0530 Message-ID: <20130911201334.7832.49714.stgit@srivatsabhat.in.ibm.com> References: <20130911201239.7832.72612.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130911201239.7832.72612.stgit@srivatsabhat.in.ibm.com> Sender: cpufreq-owner@vger.kernel.org To: rjw@sisk.pl, swarren@wwwdotorg.org, viresh.kumar@linaro.org Cc: cpufreq@vger.kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, "Srivatsa S. Bhat" List-Id: linux-pm@vger.kernel.org If update_policy_cpu() is invoked with the existing policy->cpu itself as the new-cpu parameter, then a lot of things can go terribly wrong. In its present form, update_policy_cpu() always assumes that the new-cpu is different from policy->cpu and invokes other functions to perform their respective updates. And those functions implement the actual update like this: per_cpu(..., new_cpu) = per_cpu(..., last_cpu); per_cpu(..., last_cpu) = NULL; Thus, when new_cpu == last_cpu, the final NULL assignment makes the per-cpu references vanish into thin air! (memory leak). From there, it leads to more problems: cpufreq_stats_create_table() now doesn't find the per-cpu reference and hence tries to create a new sysfs-group; but sysfs already had created the group earlier, so it complains that it cannot create a duplicate filename. In short, the repercussions of a rather innocuous invocation of update_policy_cpu() can turn out to be pretty nasty. Ideally update_policy_cpu() should handle this situation (new == last) gracefully, and not lead to such severe problems. So fix it by adding an appropriate check. Signed-off-by: Srivatsa S. Bhat Tested-by: Stephen Warren --- drivers/cpufreq/cpufreq.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 247842b..d32040c 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -949,6 +949,9 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy) static void update_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu) { + if (cpu == policy->cpu) + return; + policy->last_cpu = policy->cpu; policy->cpu = cpu;