tcp: fix behavior for epoll edge trigger (8e4d980a) · Commits · e / devices / android_kernel_fairphone_FP3

Under memory pressure, tcp_sendmsg() can fail to queue a packet while no packet is present in write queue. If we return -EAGAIN with no packet in write queue, no ACK packet will ever come to raise EPOLLOUT. We need to allow one skb per TCP socket, and make sure that tcp sockets can release their forward allocations under pressure. This is a followup to commit ("tcp: set SOCK_NOSPACE under memory pressure") Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -815,9 +815,20 @@ struct sk_buff sk_stream_alloc_skb(struct sock sk, int size, gfp_t gfp)
		/* The TCP header must be at least 32-bit aligned. */
		size = ALIGN(size, 4);

		if (unlikely(tcp_under_memory_pressure(sk)))
		sk_mem_reclaim_partial(sk);

		skb = alloc_skb_fclone(size + sk->sk_prot->max_header, gfp);
		if (skb) {
		if (sk_wmem_schedule(sk, skb->truesize)) {
		if (likely(skb)) {
		bool mem_schedule;

		if (skb_queue_len(&sk->sk_write_queue) == 0) {
		mem_schedule = true;
		sk_forced_mem_schedule(sk, skb->truesize);
		} else {
		mem_schedule = sk_wmem_schedule(sk, skb->truesize);
		}
		if (likely(mem_schedule)) {
		skb_reserve(skb, sk->sk_prot->max_header);
		/*
		* Make sure that we have exactly size bytes