net: Cleanup skb cloning by adding SKB_FCLONE_FREE

SKB_FCLONE_UNAVAILABLE has overloaded meaning depending on type of skb.
1: If skb is allocated from head_cache, it indicates fclone is not available.
2: If skb is a companion fclone skb (allocated from fclone_cache), it indicates
it is available to be used.

To avoid confusion for case 2 above, this patch  replaces
SKB_FCLONE_UNAVAILABLE with SKB_FCLONE_FREE where appropriate. For fclone
companion skbs, this indicates it is free for use.

SKB_FCLONE_UNAVAILABLE will now simply indicate skb is from head_cache and
cannot / will not have a companion fclone.

Signed-off-by: Vijay Subramanian <subramanian.vijay@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 7 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7c5036d11feb..3a5ec7638627 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -339,9 +339,10 @@ struct skb_shared_info {
 
 
 enum {
-        SKB_FCLONE_UNAVAILABLE,
-        SKB_FCLONE_ORIG,
-        SKB_FCLONE_CLONE,
+        SKB_FCLONE_UNAVAILABLE, /* skb has no fclone (from head_cache) */
+        SKB_FCLONE_ORIG,        /* orig skb (from fclone_cache) */
+        SKB_FCLONE_CLONE,       /* companion fclone skb (from fclone_cache) */
+        SKB_FCLONE_FREE,        /* this companion fclone skb is available */
 };
 
 enum {
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a0b312fa3047..28916e47f959 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -265,7 +265,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
                 skb->fclone = SKB_FCLONE_ORIG;
                 atomic_set(&fclones->fclone_ref, 1);
 
-                fclones->skb2.fclone = SKB_FCLONE_UNAVAILABLE;
+                fclones->skb2.fclone = SKB_FCLONE_FREE;
                 fclones->skb2.pfmemalloc = pfmemalloc;
         }
 out:
@@ -542,7 +542,7 @@ static void kfree_skbmem(struct sk_buff *skb)
                 fclones = container_of(skb, struct sk_buff_fclones, skb2);
 
                 /* Warning : We must perform the atomic_dec_and_test() before
-                 * setting skb->fclone back to SKB_FCLONE_UNAVAILABLE, otherwise
+                 * setting skb->fclone back to SKB_FCLONE_FREE, otherwise
                  * skb_clone() could set clone_ref to 2 before our decrement.
                  * Anyway, if we are going to free the structure, no need to
                  * rewrite skb->fclone.
@@ -553,7 +553,7 @@ static void kfree_skbmem(struct sk_buff *skb)
                         /* The clone portion is available for
                          * fast-cloning again.
                          */
-                        skb->fclone = SKB_FCLONE_UNAVAILABLE;
+                        skb->fclone = SKB_FCLONE_FREE;
                 }
                 break;
         }
@@ -874,7 +874,7 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
                 return NULL;
 
         if (skb->fclone == SKB_FCLONE_ORIG &&
-            n->fclone == SKB_FCLONE_UNAVAILABLE) {
+            n->fclone == SKB_FCLONE_FREE) {
                 n->fclone = SKB_FCLONE_CLONE;
                 /* As our fastclone was free, clone_ref must be 1 at this point.
                  * We could use atomic_inc() here, but it is faster