From: Eric Dumazet edumazet@google.com
[ Upstream commit 849b425cd091e1804af964b771761cfbefbafb43 ]
Blamed commit only dealt with applications issuing small writes.
Issue here is that we allow to force memory schedule for the sk_buff allocation, but we have no guarantee that sendmsg() is able to copy some payload in it.
In this patch, I make sure the socket can use up to tcp_wmem[0] bytes.
For example, if we consider tcp_wmem[0] = 4096 (default on x86), and initial skb->truesize being 1280, tcp_sendmsg() is able to copy up to 2816 bytes under memory pressure.
Before this patch a sendmsg() sending more than 2816 bytes would either block forever (if persistent memory pressure), or return -EAGAIN.
For bigger MTU networks, it is advised to increase tcp_wmem[0] to avoid sending too small packets.
v2: deal with zero copy paths.
Fixes: 8e4d980ac215 ("tcp: fix behavior for epoll edge trigger") Signed-off-by: Eric Dumazet edumazet@google.com Acked-by: Soheil Hassas Yeganeh soheil@google.com Reviewed-by: Wei Wang weiwan@google.com Reviewed-by: Shakeel Butt shakeelb@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp.c | 33 +++++++++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 4 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 766881775abb..3ae2ea048883 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -952,6 +952,23 @@ static int tcp_downgrade_zcopy_pure(struct sock *sk, struct sk_buff *skb) return 0; }
+static int tcp_wmem_schedule(struct sock *sk, int copy) +{ + int left; + + if (likely(sk_wmem_schedule(sk, copy))) + return copy; + + /* We could be in trouble if we have nothing queued. + * Use whatever is left in sk->sk_forward_alloc and tcp_wmem[0] + * to guarantee some progress. + */ + left = sock_net(sk)->ipv4.sysctl_tcp_wmem[0] - sk->sk_wmem_queued; + if (left > 0) + sk_forced_mem_schedule(sk, min(left, copy)); + return min(copy, sk->sk_forward_alloc); +} + static struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags, struct page *page, int offset, size_t *size) { @@ -987,7 +1004,11 @@ static struct sk_buff *tcp_build_frag(struct sock *sk, int size_goal, int flags, tcp_mark_push(tp, skb); goto new_segment; } - if (tcp_downgrade_zcopy_pure(sk, skb) || !sk_wmem_schedule(sk, copy)) + if (tcp_downgrade_zcopy_pure(sk, skb)) + return NULL; + + copy = tcp_wmem_schedule(sk, copy); + if (!copy) return NULL;
if (can_coalesce) { @@ -1336,8 +1357,11 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
copy = min_t(int, copy, pfrag->size - pfrag->offset);
- if (tcp_downgrade_zcopy_pure(sk, skb) || - !sk_wmem_schedule(sk, copy)) + if (tcp_downgrade_zcopy_pure(sk, skb)) + goto wait_for_space; + + copy = tcp_wmem_schedule(sk, copy); + if (!copy) goto wait_for_space;
err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb, @@ -1364,7 +1388,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) skb_shinfo(skb)->flags |= SKBFL_PURE_ZEROCOPY;
if (!skb_zcopy_pure(skb)) { - if (!sk_wmem_schedule(sk, copy)) + copy = tcp_wmem_schedule(sk, copy); + if (!copy) goto wait_for_space; }