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Commit d4011239 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: guarantee forward progress in tcp_sendmsg() 



Under high rx pressure, it is possible tcp_sendmsg() never has a
chance to allocate an skb and loop forever as sk_flush_backlog()
would always return true.

Fix this by calling sk_flush_backlog() only if one skb had been
allocated and filled before last backlog check.

Fixes: d41a69f1 ("tcp: make tcp_sendmsg() aware of socket backlog")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent cba65321

net/ipv4/tcp.c

+5 −2
Original line number Diff line number Diff line
@@ -1084,6 +1084,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size) 
	struct sockcm_cookie sockc;

	int flags, err, copied = 0;

	int mss_now = 0, size_goal, copied_syn = 0;

	bool process_backlog = false;

	bool sg;

	long timeo;
@@ -1167,9 +1168,10 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size) 
			if (!sk_stream_memory_free(sk))

				goto wait_for_sndbuf;



			if (sk_flush_backlog(sk))

			if (process_backlog && sk_flush_backlog(sk)) {

				process_backlog = false;

				goto restart;



			}

			skb = sk_stream_alloc_skb(sk,

						  select_size(sk, sg),

						  sk->sk_allocation,
@@ -1177,6 +1179,7 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size) 
			if (!skb)

				goto wait_for_memory;



			process_backlog = true;

			/*

			 * Check whether we can use HW checksum.

			 */