[PATCH 11/14] skbuff: drop null check from skb_zcopy

[Pavel Begunkov <asml.silence@gmail.com>]

skb_zcopy() is used all around the networkong code with many of calls
sitting in generic not necessarily zerocopy paths. Many of callers
don't ever pass a NULL skb, however a NULL check inside skb_zcopy()
can't be optimised out. As with previous patch, move the check out of
the helper to a few places where it's needed.

It removes a bunch of extra ifs in non-zerocopy paths, which is nice.
E.g. before and after:

   text    data     bss     dec     hex filename
8521472       0       0 8521472  820700 arch/x86/boot/bzImage
8521056       0       0 8521056  820560 arch/x86/boot/bzImage
delta=416B

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/skbuff.h | 2 +-
 net/core/dev.c         | 2 +-
 net/core/skbuff.c      | 3 ++-
 net/ipv4/ip_output.c   | 7 +++++--
 net/ipv4/tcp.c         | 5 ++++-
 net/ipv6/ip6_output.c  | 7 +++++--
 6 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8a7d0d03a100..7fd2b44aada0 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1469,7 +1469,7 @@ static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
 
 static inline struct ubuf_info *skb_zcopy(struct sk_buff *skb)
 {
-	bool is_zcopy = skb && skb_shinfo(skb)->flags & SKBFL_ZEROCOPY_ENABLE;
+	bool is_zcopy = skb_shinfo(skb)->flags & SKBFL_ZEROCOPY_ENABLE;
 
 	return is_zcopy ? skb_uarg(skb) : NULL;
 }
diff --git a/net/core/dev.c b/net/core/dev.c
index 83a4089990a0..877ebc0f72bd 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2239,7 +2239,7 @@ void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 	}
 out_unlock:
 	if (pt_prev) {
-		if (!skb_orphan_frags_rx(skb2, GFP_ATOMIC))
+		if (!skb2 || !skb_orphan_frags_rx(skb2, GFP_ATOMIC))
 			pt_prev->func(skb2, skb->dev, pt_prev, skb->dev);
 		else
 			kfree_skb(skb2);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e514a36bcffc..a9b8ac38dc1a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -890,7 +890,8 @@ EXPORT_SYMBOL(skb_dump);
  */
 void skb_tx_error(struct sk_buff *skb)
 {
-	skb_zcopy_clear(skb, true);
+	if (skb)
+		skb_zcopy_clear(skb, true);
 }
 EXPORT_SYMBOL(skb_tx_error);
 
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 87d4472545a5..b63f307cc5ab 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1001,10 +1001,13 @@ static int __ip_append_data(struct sock *sk,
 		csummode = CHECKSUM_PARTIAL;
 
 	if (flags & MSG_ZEROCOPY && length && sock_flag(sk, SOCK_ZEROCOPY)) {
-		uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb));
+		if (skb)
+			uarg = skb_zcopy(skb);
+		extra_uref = !uarg; /* only ref on new uarg */
+
+		uarg = msg_zerocopy_realloc(sk, length, uarg);
 		if (!uarg)
 			return -ENOBUFS;
-		extra_uref = !skb_zcopy(skb);	/* only ref on new uarg */
 		if (rt->dst.dev->features & NETIF_F_SG &&
 		    csummode == CHECKSUM_PARTIAL) {
 			paged = true;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3b75836db19b..f35e49ea08ec 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1188,7 +1188,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 	if (flags & MSG_ZEROCOPY && size && sock_flag(sk, SOCK_ZEROCOPY)) {
 		skb = tcp_write_queue_tail(sk);
-		uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
+		if (skb)
+			uarg = skb_zcopy(skb);
+
+		uarg = msg_zerocopy_realloc(sk, size, uarg);
 		if (!uarg) {
 			err = -ENOBUFS;
 			goto out_err;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 9881b61da493..41abe83c3419 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1513,10 +1513,13 @@ static int __ip6_append_data(struct sock *sk,
 		csummode = CHECKSUM_PARTIAL;
 
 	if (flags & MSG_ZEROCOPY && length && sock_flag(sk, SOCK_ZEROCOPY)) {
-		uarg = msg_zerocopy_realloc(sk, length, skb_zcopy(skb));
+		if (skb)
+			uarg = skb_zcopy(skb);
+		extra_uref = !uarg; /* only ref on new uarg */
+
+		uarg = msg_zerocopy_realloc(sk, length, uarg);
 		if (!uarg)
 			return -ENOBUFS;
-		extra_uref = !skb_zcopy(skb);	/* only ref on new uarg */
 		if (rt->dst.dev->features & NETIF_F_SG &&
 		    csummode == CHECKSUM_PARTIAL) {
 			paged = true;
-- 
2.34.1