Piteball
/
android_kernel_samsung_msm8976
mirror of https://github.com/team-infusion-developers/android_kernel_samsung_msm8976.git
1
1
Fork 0
Code Issues Projects Releases Wiki Activity

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>
Git-commit: 999976e0f6233322a878b0b7148c810544d6c8a8
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[lix@codeaurora.org: resolve trivial merge conflicts]
Change-Id: I3a30979a551c88711ccc0f4ba9e847c03a0478ed
Signed-off-by: Xiaocheng Li <lix@codeaurora.org>
This commit is contained in:
Aaron Plattner 2014-03-04 12:42:15 -08:00 committed by Xiaocheng Li
parent 660309ee81
commit 928229f838
1 changed files with 7 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
drivers/cpufreq/cpufreq.c
View File

@ -1495,28 +1495,16 @@ static unsigned int __cpufreq_get(unsigned int cpu)
*/
unsigned int cpufreq_get(unsigned int cpu)
{
struct cpufreq_policy *policy;
struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
unsigned int ret_freq = 0;
unsigned long flags;
if (cpufreq_disabled() || !cpufreq_driver)
return -ENOENT;
if (policy) {
down_read(&policy->rwsem);
ret_freq = __cpufreq_get(cpu);
up_read(&policy->rwsem);
read_lock_irqsave(&cpufreq_driver_lock, flags);
policy = per_cpu(cpufreq_cpu_data, cpu);
read_unlock_irqrestore(&cpufreq_driver_lock, flags);
BUG_ON(!policy);
if (!down_read_trylock(&cpufreq_rwsem))
return 0;
down_read(&policy->rwsem);
ret_freq = __cpufreq_get(cpu);
up_read(&policy->rwsem);
up_read(&cpufreq_rwsem);
cpufreq_cpu_put(policy);
}
return ret_freq;
}