intel_cacheinfo: potential NULL dereference?

index 33eae20..a7e358f 100644
@@ -399,16 +399,15 @@ amd_check_l3_disable(int index, struct _cpuid4_info_regs *this_leaf)
 static ssize_t show_cache_disable(struct _cpuid4_info *this_leaf, char *buf,
 				  unsigned int slot)
 {
-	struct pci_dev *dev = this_leaf->l3->dev;
 	unsigned int reg = 0;
 
 	if (!this_leaf->l3 || !this_leaf->l3->can_disable)
 		return -EINVAL;
 
-	if (!dev)
+	if (!this_leaf->l3->dev)
 		return -EINVAL;
 
-	pci_read_config_dword(dev, 0x1BC + slot * 4, &reg);
+	pci_read_config_dword(this_leaf->l3->dev, 0x1BC + slot * 4, &reg);
 	return sprintf(buf, "0x%08x\n", reg);
 }
 

@@ -456,7 +455,6 @@ static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
 				   const char *buf, size_t count,
 				   unsigned int slot)
 {
-	struct pci_dev *dev = this_leaf->l3->dev;
 	int cpu = cpumask_first(to_cpumask(this_leaf->shared_cpu_map));
 	unsigned long val = 0;
 

@@ -469,7 +467,7 @@ static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!dev)
+	if (!this_leaf->l3->dev)
 		return -EINVAL;
 
 	if (strict_strtoul(buf, 10, &val) < 0)

index a7e358f..898c2f4 100644
@@ -347,8 +347,8 @@ static struct amd_l3_cache * __cpuinit amd_init_l3_cache(int node)
 	return l3;
 }
 
-static void __cpuinit
-amd_check_l3_disable(int index, struct _cpuid4_info_regs *this_leaf)
+static void __cpuinit amd_check_l3_disable(struct _cpuid4_info_regs *this_leaf,
+					   int index)
 {
 	int node;
 

@@ -396,19 +396,39 @@ amd_check_l3_disable(int index, struct _cpuid4_info_regs *this_leaf)
 	this_leaf->l3 = l3_caches[node];
 }
 
+/*
+ * check whether a slot used for disabling an L3 index is occupied.
+ * @l3: L3 cache descriptor
+ * @slot: slot number (0..1)
+ *
+ * @returns: the disabled index if used or negative value if slot free.
+ */
+int amd_get_l3_disable_slot(struct amd_l3_cache *l3, unsigned slot)
+{
+	unsigned int reg = 0;
+
+	pci_read_config_dword(l3->dev, 0x1BC + slot * 4, &reg);
+
+	/* check whether this slot is activated already */
+	if (reg & (3UL << 30))
+		return reg & 0xfff;
+
+	return -1;
+}
+
 static ssize_t show_cache_disable(struct _cpuid4_info *this_leaf, char *buf,
 				  unsigned int slot)
 {
-	unsigned int reg = 0;
+	int index;
 
 	if (!this_leaf->l3 || !this_leaf->l3->can_disable)
 		return -EINVAL;
 
-	if (!this_leaf->l3->dev)
-		return -EINVAL;
+	index = amd_get_l3_disable_slot(this_leaf->l3, slot);
+	if (index >= 0)
+		return sprintf(buf, "%d\n", index);
 
-	pci_read_config_dword(this_leaf->l3->dev, 0x1BC + slot * 4, &reg);
-	return sprintf(buf, "0x%08x\n", reg);
+	return sprintf(buf, "FREE\n");
 }
 
 #define SHOW_CACHE_DISABLE(slot)					\

@@ -450,36 +470,74 @@ static void amd_l3_disable_index(struct amd_l3_cache *l3, int cpu,
 	}
 }
 
-
-static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
-				   const char *buf, size_t count,
-				   unsigned int slot)
+/*
+ * disable a L3 cache index by using a disable-slot
+ *
+ * @l3:    L3 cache descriptor
+ * @cpu:   A CPU on the node containing the L3 cache
+ * @slot:  slot number (0..1)
+ * @index: index to disable
+ *
+ * @return: 0 on success, error status on failure
+ */
+int amd_set_l3_disable_slot(struct amd_l3_cache *l3, int cpu, unsigned slot,
+			    unsigned long index)
 {
-	int cpu = cpumask_first(to_cpumask(this_leaf->shared_cpu_map));
-	unsigned long val = 0;
+	int ret = 0;
 
 #define SUBCACHE_MASK	(3UL << 20)
 #define SUBCACHE_INDEX	0xfff
 
-	if (!this_leaf->l3 || !this_leaf->l3->can_disable)
+	/*
+	 * check whether this slot is already used or
+	 * the index is already disabled
+	 */
+	ret = amd_get_l3_disable_slot(l3, slot);
+	if (ret >= 0)
 		return -EINVAL;
 
+	/*
+	 * check whether the other slot has disabled the
+	 * same index already
+	 */
+	if (index == amd_get_l3_disable_slot(l3, !slot))
+		return -EINVAL;
+
+	/* do not allow writes outside of allowed bits */
+	if ((index & ~(SUBCACHE_MASK | SUBCACHE_INDEX)) ||
+	    ((index & SUBCACHE_INDEX) > l3->indices))
+		return -EINVAL;
+
+	amd_l3_disable_index(l3, cpu, slot, index);
+
+	return 0;
+}
+
+static ssize_t store_cache_disable(struct _cpuid4_info *this_leaf,
+				  const char *buf, size_t count,
+				  unsigned int slot)
+{
+	unsigned long val = 0;
+	int cpu, err = 0;
+
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	if (!this_leaf->l3->dev)
+	if (!this_leaf->l3 || !this_leaf->l3->can_disable)
 		return -EINVAL;
 
-	if (strict_strtoul(buf, 10, &val) < 0)
-		return -EINVAL;
+	cpu = cpumask_first(to_cpumask(this_leaf->shared_cpu_map));
 
-	/* do not allow writes outside of allowed bits */
-	if ((val & ~(SUBCACHE_MASK | SUBCACHE_INDEX)) ||
-	    ((val & SUBCACHE_INDEX) > this_leaf->l3->indices))
+	if (strict_strtoul(buf, 10, &val) < 0)
 		return -EINVAL;
 
-	amd_l3_disable_index(this_leaf->l3, cpu, slot, val);
-
+	err = amd_set_l3_disable_slot(this_leaf->l3, cpu, slot, val);
+	if (err) {
+		if (err == -EEXIST)
+			printk(KERN_WARNING "L3 disable slot %d in use!\n",
+					    slot);
+		return err;
+	}
 	return count;
 }
 

@@ -500,7 +558,7 @@ static struct _cache_attr cache_disable_1 = __ATTR(cache_disable_1, 0644,
 
 #else	/* CONFIG_CPU_SUP_AMD */
 static void __cpuinit
-amd_check_l3_disable(int index, struct _cpuid4_info_regs *this_leaf)
+amd_check_l3_disable(struct _cpuid4_info_regs *this_leaf, int index)
 {
 };
 #endif /* CONFIG_CPU_SUP_AMD */

@@ -516,7 +574,7 @@ __cpuinit cpuid4_cache_lookup_regs(int index,
 
 	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
 		amd_cpuid4(index, &eax, &ebx, &ecx);
-		amd_check_l3_disable(index, this_leaf);
+		amd_check_l3_disable(this_leaf, index);
 	} else {
 		cpuid_count(4, index, &eax.full, &ebx.full, &ecx.full, &edx);
 	}