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authorAaron Plattner <aplattner@nvidia.com>2014-03-04 12:42:15 -0800
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-03-06 13:25:16 +0100
commit999976e0f6233322a878b0b7148c810544d6c8a8 (patch)
treedf07413e3d9018e7ee7c439bc697c93cb52a61b3
parent0414855fdc4a40da05221fc6062cccbc0c30f169 (diff)
downloadlinux-999976e0f6233322a878b0b7148c810544d6c8a8.tar.gz
cpufreq: use cpufreq_cpu_get() to avoid cpufreq_get() race conditions
If a module calls cpufreq_get while cpufreq is initializing, it's possible for it to be called after cpufreq_driver is set but before cpufreq_cpu_data is written during subsys_interface_register. This happens because cpufreq_get doesn't take the cpufreq_driver_lock around its use of cpufreq_cpu_data. Fix this by using cpufreq_cpu_get(cpu) to look up the policy rather than reading it out of cpufreq_cpu_data directly. cpufreq_cpu_get() takes the appropriate locks to prevent this race from happening. Since it's possible for policy to be NULL if the caller passes in an invalid CPU number or calls the function before cpufreq is initialized, delete the BUG_ON(!policy) and simply return 0. Don't try to return -ENOENT because that's negative and the function returns an unsigned integer. References: https://bbs.archlinux.org/viewtopic.php?id=177934 Signed-off-by: Aaron Plattner <aplattner@nvidia.com> Cc: 3.13+ <stable@vger.kernel.org> # 3.13+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
-rw-r--r--drivers/cpufreq/cpufreq.c21
1 files changed, 7 insertions, 14 deletions
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index cb003a6b72c8..c4cacabbbb55 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1546,23 +1546,16 @@ static unsigned int __cpufreq_get(unsigned int cpu)
*/
unsigned int cpufreq_get(unsigned int cpu)
{
- struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
+ struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
unsigned int ret_freq = 0;
- if (cpufreq_disabled() || !cpufreq_driver)
- return -ENOENT;
-
- BUG_ON(!policy);
-
- if (!down_read_trylock(&cpufreq_rwsem))
- return 0;
-
- down_read(&policy->rwsem);
-
- ret_freq = __cpufreq_get(cpu);
+ if (policy) {
+ down_read(&policy->rwsem);
+ ret_freq = __cpufreq_get(cpu);
+ up_read(&policy->rwsem);
- up_read(&policy->rwsem);
- up_read(&cpufreq_rwsem);
+ cpufreq_cpu_put(policy);
+ }
return ret_freq;
}