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tcp: fix possible freeze in tx path under memory pressure

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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: 8e4d980ac2 ("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>
This commit is contained in:
Eric Dumazet 2022-06-14 10:17:34 -07:00 committed by David S. Miller
parent c4ee118561
commit 849b425cd0
1 changed files with 29 additions and 4 deletions
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33
net/ipv4/tcp.c
View file

@ -951,6 +951,23 @@ 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)
{
@ -986,7 +1003,11 @@ 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) {
@ -1334,8 +1355,11 @@ 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,
@ -1362,7 +1386,8 @@ 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;
}