inetpeer: restore small inet_peer structures

Addition of rcu_head to struct inet_peer added 16bytes on 64bit arches.

Thats a bit unfortunate, since old size was exactly 64 bytes.

This can be solved, using an union between this rcu_head an four fields,
that are normally used only when a refcount is taken on inet_peer.
rcu_head is used only when refcnt=-1, right before structure freeing.

Add a inet_peer_refcheck() function to check this assertion for a while.

We can bring back SLAB_HWCACHE_ALIGN qualifier in kmem cache creation.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 5 deletions

diff --git a/include/net/inetpeer.h b/include/net/inetpeer.h
index 617404730422..417d0c894f29 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -22,11 +22,21 @@ struct inet_peer {
 	__u32			dtime;		/* the time of last use of not
 						 * referenced entries */
 	atomic_t		refcnt;
-	atomic_t		rid;		/* Frag reception counter */
-	atomic_t		ip_id_count;	/* IP ID for the next packet */
-	__u32			tcp_ts;
-	__u32			tcp_ts_stamp;
-	struct rcu_head		rcu;
+	/*
+	 * Once inet_peer is queued for deletion (refcnt == -1), following fields
+	 * are not available: rid, ip_id_count, tcp_ts, tcp_ts_stamp
+	 * We can share memory with rcu_head to keep inet_peer small
+	 * (less then 64 bytes)
+	 */
+	union {
+		struct {
+			atomic_t	rid;		/* Frag reception counter */
+			atomic_t	ip_id_count;	/* IP ID for the next packet */
+			__u32		tcp_ts;
+			__u32		tcp_ts_stamp;
+		};
+		struct rcu_head         rcu;
+	};
 };
 
 void			inet_initpeers(void) __init;
@@ -37,10 +47,21 @@ struct inet_peer	*inet_getpeer(__be32 daddr, int create);
 /* can be called from BH context or outside */
 extern void inet_putpeer(struct inet_peer *p);
 
+/*
+ * temporary check to make sure we dont access rid, ip_id_count, tcp_ts,
+ * tcp_ts_stamp if no refcount is taken on inet_peer
+ */
+static inline void inet_peer_refcheck(const struct inet_peer *p)
+{
+	WARN_ON_ONCE(atomic_read(&p->refcnt) <= 0);
+}
+
+
 /* can be called with or without local BH being disabled */
 static inline __u16	inet_getid(struct inet_peer *p, int more)
 {
 	more++;
+	inet_peer_refcheck(p);
 	return atomic_add_return(more, &p->ip_id_count) - more;
 }