net: allow __skb_ext_alloc to sleep

mptcp calls this from the transmit side, from process context.
Allow a sleeping allocation instead of unconditional GFP_ATOMIC.
Acked-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -4165,7 +4165,7 @@ struct skb_ext {
 	char data[] __aligned(8);
 };
 
-struct skb_ext *__skb_ext_alloc(void);
+struct skb_ext *__skb_ext_alloc(gfp_t flags);
 void *__skb_ext_set(struct sk_buff *skb, enum skb_ext_id id,
 		    struct skb_ext *ext);
 void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id);

net/core/skbuff.c

@@ -6087,13 +6087,15 @@ static void *skb_ext_get_ptr(struct skb_ext *ext, enum skb_ext_id id)
 /**
  * __skb_ext_alloc - allocate a new skb extensions storage
  *
+ * @flags: See kmalloc().
+ *
  * Returns the newly allocated pointer. The pointer can later attached to a
  * skb via __skb_ext_set().
  * Note: caller must handle the skb_ext as an opaque data.
  */
-struct skb_ext *__skb_ext_alloc(void)
+struct skb_ext *__skb_ext_alloc(gfp_t flags)
 {
-	struct skb_ext *new = kmem_cache_alloc(skbuff_ext_cache, GFP_ATOMIC);
+	struct skb_ext *new = kmem_cache_alloc(skbuff_ext_cache, flags);
 
 	if (new) {
 		memset(new->offset, 0, sizeof(new->offset));
@@ -6188,7 +6190,7 @@ void *skb_ext_add(struct sk_buff *skb, enum skb_ext_id id)
 	} else {
 		newoff = SKB_EXT_CHUNKSIZEOF(*new);
 
-		new = __skb_ext_alloc();
+		new = __skb_ext_alloc(GFP_ATOMIC);
 		if (!new)
 			return NULL;
 	}

net/mptcp/protocol.c

@@ -367,8 +367,10 @@ static void mptcp_stop_timer(struct sock *sk)
 
 static bool mptcp_ext_cache_refill(struct mptcp_sock *msk)
 {
+	const struct sock *sk = (const struct sock *)msk;
+
 	if (!msk->cached_ext)
-		msk->cached_ext = __skb_ext_alloc();
+		msk->cached_ext = __skb_ext_alloc(sk->sk_allocation);
 
 	return !!msk->cached_ext;
 }