SELinux: code readability with avc_cache

The code making use of struct avc_cache was not easy to read thanks to liberal
use of &avc_cache.{slots_lock,slots}[hvalue] throughout.  This patch simply
creates local pointers and uses those instead of the long global names.
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/avc.c

@@ -92,12 +92,12 @@ struct avc_entry {
 
 struct avc_node {
 	struct avc_entry	ae;
-	struct list_head	list;
+	struct list_head	list; /* anchored in avc_cache->slots[i] */
 	struct rcu_head		rhead;
 };
 
 struct avc_cache {
-	struct list_head	slots[AVC_CACHE_SLOTS];
+	struct list_head	slots[AVC_CACHE_SLOTS]; /* head for avc_node->list */
 	spinlock_t		slots_lock[AVC_CACHE_SLOTS]; /* lock for writes */
 	atomic_t		lru_hint;	/* LRU hint for reclaim scan */
 	atomic_t		active_nodes;
@@ -249,16 +249,18 @@ int avc_get_hash_stats(char *page)
 {
 	int i, chain_len, max_chain_len, slots_used;
 	struct avc_node *node;
+	struct list_head *head;
 
 	rcu_read_lock();
 
 	slots_used = 0;
 	max_chain_len = 0;
 	for (i = 0; i < AVC_CACHE_SLOTS; i++) {
-		if (!list_empty(&avc_cache.slots[i])) {
+		head = &avc_cache.slots[i];
+		if (!list_empty(head)) {
 			slots_used++;
 			chain_len = 0;
-			list_for_each_entry_rcu(node, &avc_cache.slots[i], list)
+			list_for_each_entry_rcu(node, head, list)
 				chain_len++;
 			if (chain_len > max_chain_len)
 				max_chain_len = chain_len;
@@ -306,26 +308,30 @@ static inline int avc_reclaim_node(void)
 	struct avc_node *node;
 	int hvalue, try, ecx;
 	unsigned long flags;
+	struct list_head *head;
+	spinlock_t *lock;
 
 	for (try = 0, ecx = 0; try < AVC_CACHE_SLOTS; try++) {
 		hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);
+		head = &avc_cache.slots[hvalue];
+		lock = &avc_cache.slots_lock[hvalue];
 
-		if (!spin_trylock_irqsave(&avc_cache.slots_lock[hvalue], flags))
+		if (!spin_trylock_irqsave(lock, flags))
 			continue;
 
 		rcu_read_lock();
-		list_for_each_entry(node, &avc_cache.slots[hvalue], list) {
+		list_for_each_entry(node, head, list) {
 			avc_node_delete(node);
 			avc_cache_stats_incr(reclaims);
 			ecx++;
 			if (ecx >= AVC_CACHE_RECLAIM) {
 				rcu_read_unlock();
-				spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
+				spin_unlock_irqrestore(lock, flags);
 				goto out;
 			}
 		}
 		rcu_read_unlock();
-		spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
+		spin_unlock_irqrestore(lock, flags);
 	}
 out:
 	return ecx;
@@ -362,9 +368,11 @@ static inline struct avc_node *avc_search_node(u32 ssid, u32 tsid, u16 tclass)
 {
 	struct avc_node *node, *ret = NULL;
 	int hvalue;
+	struct list_head *head;
 
 	hvalue = avc_hash(ssid, tsid, tclass);
-	list_for_each_entry_rcu(node, &avc_cache.slots[hvalue], list) {
+	head = &avc_cache.slots[hvalue];
+	list_for_each_entry_rcu(node, head, list) {
 		if (ssid == node->ae.ssid &&
 		    tclass == node->ae.tclass &&
 		    tsid == node->ae.tsid) {
@@ -453,11 +461,17 @@ static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_dec
 
 	node = avc_alloc_node();
 	if (node) {
+		struct list_head *head;
+		spinlock_t *lock;
+
 		hvalue = avc_hash(ssid, tsid, tclass);
 		avc_node_populate(node, ssid, tsid, tclass, avd);
 
-		spin_lock_irqsave(&avc_cache.slots_lock[hvalue], flag);
-		list_for_each_entry(pos, &avc_cache.slots[hvalue], list) {
+		head = &avc_cache.slots[hvalue];
+		lock = &avc_cache.slots_lock[hvalue];
+
+		spin_lock_irqsave(lock, flag);
+		list_for_each_entry(pos, head, list) {
 			if (pos->ae.ssid == ssid &&
 			    pos->ae.tsid == tsid &&
 			    pos->ae.tclass == tclass) {
@@ -465,9 +479,9 @@ static struct avc_node *avc_insert(u32 ssid, u32 tsid, u16 tclass, struct av_dec
 				goto found;
 			}
 		}
-		list_add_rcu(&node->list, &avc_cache.slots[hvalue]);
+		list_add_rcu(&node->list, head);
 found:
-		spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flag);
+		spin_unlock_irqrestore(lock, flag);
 	}
 out:
 	return node;
@@ -736,6 +750,8 @@ static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
 	int hvalue, rc = 0;
 	unsigned long flag;
 	struct avc_node *pos, *node, *orig = NULL;
+	struct list_head *head;
+	spinlock_t *lock;
 
 	node = avc_alloc_node();
 	if (!node) {
@@ -745,9 +761,13 @@ static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
 
 	/* Lock the target slot */
 	hvalue = avc_hash(ssid, tsid, tclass);
-	spin_lock_irqsave(&avc_cache.slots_lock[hvalue], flag);
 
-	list_for_each_entry(pos, &avc_cache.slots[hvalue], list) {
+	head = &avc_cache.slots[hvalue];
+	lock = &avc_cache.slots_lock[hvalue];
+
+	spin_lock_irqsave(lock, flag);
+
+	list_for_each_entry(pos, head, list) {
 		if (ssid == pos->ae.ssid &&
 		    tsid == pos->ae.tsid &&
 		    tclass == pos->ae.tclass &&
@@ -792,7 +812,7 @@ static int avc_update_node(u32 event, u32 perms, u32 ssid, u32 tsid, u16 tclass,
 	}
 	avc_node_replace(node, orig);
 out_unlock:
-	spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flag);
+	spin_unlock_irqrestore(lock, flag);
 out:
 	return rc;
 }
@@ -807,18 +827,23 @@ int avc_ss_reset(u32 seqno)
 	int i, rc = 0, tmprc;
 	unsigned long flag;
 	struct avc_node *node;
+	struct list_head *head;
+	spinlock_t *lock;
 
 	for (i = 0; i < AVC_CACHE_SLOTS; i++) {
-		spin_lock_irqsave(&avc_cache.slots_lock[i], flag);
+		head = &avc_cache.slots[i];
+		lock = &avc_cache.slots_lock[i];
+
+		spin_lock_irqsave(lock, flag);
 		/*
 		 * With preemptable RCU, the outer spinlock does not
 		 * prevent RCU grace periods from ending.
 		 */
 		rcu_read_lock();
-		list_for_each_entry(node, &avc_cache.slots[i], list)
+		list_for_each_entry(node, head, list)
 			avc_node_delete(node);
 		rcu_read_unlock();
-		spin_unlock_irqrestore(&avc_cache.slots_lock[i], flag);
+		spin_unlock_irqrestore(lock, flag);
 	}
 
 	for (c = avc_callbacks; c; c = c->next) {