[PATCH] audit: remove the audit freelist

[Florian Westphal]

allows better debugging as freeing audit buffers now always honors slub
debug hooks (e.g. object poisoning) and leak checker can detect the
free operation.

Removal also results in a small speedup (using
single rule 'iptables -A INPUT -i lo -j AUDIT --type drop'):

super_netperf 4 -H 127.0.0.1 -l 360 -t UDP_RR -- -R 1 -m 64
Before:
294953
After:
298013

(alloc/free no longer serializes on spinlock, allocator can use percpu
 pool).

Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
 kernel/audit.c | 53 ++++++++---------------------------------------------
 1 file changed, 8 insertions(+), 45 deletions(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index f1ca11613379..396868dc523a 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -131,13 +131,6 @@ static int audit_net_id;
 /* Hash for inode-based rules */
 struct list_head audit_inode_hash[AUDIT_INODE_BUCKETS];
 
-/* The audit_freelist is a list of pre-allocated audit buffers (if more
- * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
- * being placed on the freelist). */
-static DEFINE_SPINLOCK(audit_freelist_lock);
-static int	   audit_freelist_count;
-static LIST_HEAD(audit_freelist);
-
 static struct sk_buff_head audit_skb_queue;
 /* queue of skbs to send to auditd when/if it comes back */
 static struct sk_buff_head audit_skb_hold_queue;
@@ -164,17 +157,11 @@ DEFINE_MUTEX(audit_cmd_mutex);
  * should be at least that large. */
 #define AUDIT_BUFSIZ 1024
 
-/* AUDIT_MAXFREE is the number of empty audit_buffers we keep on the
- * audit_freelist.  Doing so eliminates many kmalloc/kfree calls. */
-#define AUDIT_MAXFREE  (2*NR_CPUS)
-
-/* The audit_buffer is used when formatting an audit record.  The caller
- * locks briefly to get the record off the freelist or to allocate the
- * buffer, and locks briefly to send the buffer to the netlink layer or
+/* The audit_buffer is used when formatting an audit record.
+ * The caller locks briefly to send the buffer to the netlink layer or
  * to place it on a transmit queue.  Multiple audit_buffers can be in
  * use simultaneously. */
 struct audit_buffer {
-	struct list_head     list;
 	struct sk_buff       *skb;	/* formatted skb ready to send */
 	struct audit_context *ctx;	/* NULL or associated context */
 	gfp_t		     gfp_mask;
@@ -1247,43 +1234,22 @@ __setup("audit_backlog_limit=", audit_backlog_limit_set);
 
 static void audit_buffer_free(struct audit_buffer *ab)
 {
-	unsigned long flags;
-
 	if (!ab)
 		return;
 
 	kfree_skb(ab->skb);
-	spin_lock_irqsave(&audit_freelist_lock, flags);
-	if (audit_freelist_count > AUDIT_MAXFREE)
-		kfree(ab);
-	else {
-		audit_freelist_count++;
-		list_add(&ab->list, &audit_freelist);
-	}
-	spin_unlock_irqrestore(&audit_freelist_lock, flags);
+	kfree(ab);
 }
 
 static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
 						gfp_t gfp_mask, int type)
 {
-	unsigned long flags;
-	struct audit_buffer *ab = NULL;
+	struct audit_buffer *ab;
 	struct nlmsghdr *nlh;
 
-	spin_lock_irqsave(&audit_freelist_lock, flags);
-	if (!list_empty(&audit_freelist)) {
-		ab = list_entry(audit_freelist.next,
-				struct audit_buffer, list);
-		list_del(&ab->list);
-		--audit_freelist_count;
-	}
-	spin_unlock_irqrestore(&audit_freelist_lock, flags);
-
-	if (!ab) {
-		ab = kmalloc(sizeof(*ab), gfp_mask);
-		if (!ab)
-			goto err;
-	}
+	ab = kmalloc(sizeof(*ab), gfp_mask);
+	if (!ab)
+		return NULL;
 
 	ab->ctx = ctx;
 	ab->gfp_mask = gfp_mask;
@@ -1294,13 +1260,10 @@ static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
 
 	nlh = nlmsg_put(ab->skb, 0, 0, type, 0, 0);
 	if (!nlh)
-		goto out_kfree_skb;
+		goto err;
 
 	return ab;
 
-out_kfree_skb:
-	kfree_skb(ab->skb);
-	ab->skb = NULL;
 err:
 	audit_buffer_free(ab);
 	return NULL;
-- 
2.7.3