linux-kernel - [PATCH] [CPUFREQ] fix race condition in store_scaling

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Message-ID: <4BE967B9.5050107@udo.edu>
Date:	Tue, 11 May 2010 16:20:41 +0200
From:	Andrej Gelenberg <andrej.gelenberg@....edu>
To:	linux@...do.de, ashok.raj@...el.com, jacob.shin@....com
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: [PATCH] [CPUFREQ] fix race condition in store_scaling_governor

Wrap store_scaling_governor with mutex lock cpufreq_governor_mutex.
Fix kernel panic if switch scaling governor very fast.
Bug in bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=15948

Signed-off-by: Andrej Gelenberg <andrej.gelenberg@....edu>
---
  drivers/cpufreq/cpufreq.c |   16 +++++++++++-----
  1 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 75d293e..6ba42f9 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -403,8 +403,6 @@ static int cpufreq_parse_governor(char 
*str_governor, unsigned int *policy,
  	} else if (cpufreq_driver->target) {
  		struct cpufreq_governor *t;

-		mutex_lock(&cpufreq_governor_mutex);
-
  		t = __find_governor(str_governor);

  		if (t == NULL) {
@@ -429,8 +427,6 @@ static int cpufreq_parse_governor(char 
*str_governor, unsigned int *policy,
  			*governor = t;
  			err = 0;
  		}
-
-		mutex_unlock(&cpufreq_governor_mutex);
  	}
  out:
  	return err;
@@ -521,7 +517,7 @@ static ssize_t show_scaling_governor(struct 
cpufreq_policy *policy, char *buf)
  /**
   * store_scaling_governor - store policy for the specified CPU
   */
-static ssize_t store_scaling_governor(struct cpufreq_policy *policy,
+static ssize_t _store_scaling_governor(struct cpufreq_policy *policy,
  					const char *buf, size_t count)
  {
  	unsigned int ret = -EINVAL;
@@ -553,6 +549,16 @@ static ssize_t store_scaling_governor(struct 
cpufreq_policy *policy,
  		return count;
  }

+static ssize_t store_scaling_governor(struct cpufreq_policy *policy,
+                                        const char *buf, size_t count)
+{
+        ssize_t ret;
+	mutex_lock(&cpufreq_governor_mutex);
+        ret = _store_scaling_governor(policy, buf, count);
+	mutex_unlock(&cpufreq_governor_mutex);
+        return ret;
+}
+
  /**
   * show_scaling_driver - show the cpufreq driver currently loaded
   */
-- 
1.7.1

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