Messages in this thread Patch in this message | | | 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 |
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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 <srivatsa.bhat@linux.vnet.ibm.com> Tested-by: Stephen Warren <swarren@nvidia.com> ---
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;
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