This is a note to let you know that I've just added the patch titled tcp: fix possible freeze in tx path under memory pressure to the 5.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tcp-fix-possible-freeze-in-tx-path-under-memory-pres.patch and it can be found in the queue-5.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit cdb5196c370be0b905af4fa1c9a7bd6410407d4e Author: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Tue Jun 14 10:17:34 2022 -0700 tcp: fix possible freeze in tx path under memory pressure [ 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@xxxxxxxxxx> Acked-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Reviewed-by: Wei Wang <weiwan@xxxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> 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; }