Re: [PATCH] cpufreq lock rewrite bugfix - Fix locking in cpufreq_get

[Venkatesh Pallipadi]

Incremental bugfix to previous 3 patch patchset of cpufreq lock rewrite.

There was one code path in cpufreq_get, that was using the write lock
in place of read and also potential recursive lock with sysfs
interface of cpuinfo_cur_freq.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>

Index: linux-2.6.20-rc-mm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-2.6.20-rc-mm.orig/drivers/cpufreq/cpufreq.c
+++ linux-2.6.20-rc-mm/drivers/cpufreq/cpufreq.c
@@ -101,6 +101,7 @@ EXPORT_SYMBOL_GPL(unlock_policy_rwsem_wr
 
 /* internal prototypes */
 static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned int event);
+static unsigned int __cpufreq_get(unsigned int cpu);
 static void handle_update(struct work_struct *work);
 
 /**
@@ -488,7 +489,7 @@ store_one(scaling_max_freq,max);
 static ssize_t show_cpuinfo_cur_freq (struct cpufreq_policy * policy,
 							char *buf)
 {
-	unsigned int cur_freq = cpufreq_get(policy->cpu);
+	unsigned int cur_freq = __cpufreq_get(policy->cpu);
 	if (!cur_freq)
 		return sprintf(buf, "<unknown>");
 	return sprintf(buf, "%u\n", cur_freq);
@@ -1074,25 +1075,13 @@ unsigned int cpufreq_quick_get(unsigned 
 EXPORT_SYMBOL(cpufreq_quick_get);
 
 
-/**
- * cpufreq_get - get the current CPU frequency (in kHz)
- * @cpu: CPU number
- *
- * Get the CPU current (static) CPU frequency
- */
-unsigned int cpufreq_get(unsigned int cpu)
+static unsigned int __cpufreq_get(unsigned int cpu)
 {
-	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+	struct cpufreq_policy *policy = cpufreq_cpu_data[cpu];
 	unsigned int ret_freq = 0;
 
-	if (!policy)
-		return 0;
-
 	if (!cpufreq_driver->get)
-		goto out;
-
-	if (unlikely(lock_policy_rwsem_write(cpu)))
-		goto out;
+		return (ret_freq);
 
 	ret_freq = cpufreq_driver->get(cpu);
 
@@ -1106,11 +1095,32 @@ unsigned int cpufreq_get(unsigned int cp
 		}
 	}
 
-	unlock_policy_rwsem_write(cpu);
+	return (ret_freq);
+}
+
+/**
+ * cpufreq_get - get the current CPU frequency (in kHz)
+ * @cpu: CPU number
+ *
+ * Get the CPU current (static) CPU frequency
+ */
+unsigned int cpufreq_get(unsigned int cpu)
+{
+	unsigned int ret_freq = 0;
+	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+
+	if (!policy)
+		goto out;
+
+	if (unlikely(lock_policy_rwsem_read(cpu)))
+		goto out;
+
+	ret_freq = __cpufreq_get(cpu);
+
+	unlock_policy_rwsem_read(cpu);
 
 out:
 	cpufreq_cpu_put(policy);
-
 	return (ret_freq);
 }
 EXPORT_SYMBOL(cpufreq_get);
-
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