skbuff: Push status and refcounts into sock_zerocopy_callback

Before this change, the caller of sock_zerocopy_callback would
need to save the zerocopy status, decrement and check the refcount,
and then call the callback function - the callback was only invoked
when the refcount reached zero.

Now, the caller just passes the status into the callback function,
which saves the status and handles its own refcounts.

This makes the behavior of the sock_zerocopy_callback identical
to the tpacket and vhost callbacks.
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/skbuff.h

@@ -1479,9 +1479,6 @@ static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
 	if (uarg) {
 		if (skb_zcopy_is_nouarg(skb)) {
 			/* no notification callback */
-		} else if (uarg->callback == sock_zerocopy_callback) {
-			uarg->zerocopy = uarg->zerocopy && zerocopy;
-			sock_zerocopy_put(uarg);
 		} else {
 			uarg->callback(uarg, zerocopy);
 		}

net/core/skbuff.c

@@ -1194,7 +1194,7 @@ static bool skb_zerocopy_notify_extend(struct sk_buff *skb, u32 lo, u16 len)
 	return true;
 }
 
-void sock_zerocopy_callback(struct ubuf_info *uarg, bool success)
+static void __sock_zerocopy_callback(struct ubuf_info *uarg)
 {
 	struct sk_buff *tail, *skb = skb_from_uarg(uarg);
 	struct sock_exterr_skb *serr;
@@ -1222,7 +1222,7 @@ void sock_zerocopy_callback(struct ubuf_info *uarg, bool success)
 	serr->ee.ee_origin = SO_EE_ORIGIN_ZEROCOPY;
 	serr->ee.ee_data = hi;
 	serr->ee.ee_info = lo;
-	if (!success)
+	if (!uarg->zerocopy)
 		serr->ee.ee_code |= SO_EE_CODE_ZEROCOPY_COPIED;
 
 	q = &sk->sk_error_queue;
@@ -1241,11 +1241,19 @@ void sock_zerocopy_callback(struct ubuf_info *uarg, bool success)
 	consume_skb(skb);
 	sock_put(sk);
 }
+
+void sock_zerocopy_callback(struct ubuf_info *uarg, bool success)
+{
+	uarg->zerocopy = uarg->zerocopy & success;
+
+	if (refcount_dec_and_test(&uarg->refcnt))
+		__sock_zerocopy_callback(uarg);
+}
 EXPORT_SYMBOL_GPL(sock_zerocopy_callback);
 
 void sock_zerocopy_put(struct ubuf_info *uarg)
 {
-	if (uarg && refcount_dec_and_test(&uarg->refcnt))
+	if (uarg)
 		uarg->callback(uarg, uarg->zerocopy);
 }
 EXPORT_SYMBOL_GPL(sock_zerocopy_put);