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;
}
