This is a note to let you know that I've just added the patch titled
tcp: avoid premature drops in tcp_add_backlog()
to the 5.15-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-avoid-premature-drops-in-tcp_add_backlog.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 926e38a67f64f3abf1d56bf614f472e7f9995b91
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Tue Apr 23 12:56:20 2024 +0000
tcp: avoid premature drops in tcp_add_backlog()
[ Upstream commit ec00ed472bdb7d0af840da68c8c11bff9f4d9caa ]
While testing TCP performance with latest trees,
I saw suspect SOCKET_BACKLOG drops.
tcp_add_backlog() computes its limit with :
limit = (u32)READ_ONCE(sk->sk_rcvbuf) +
(u32)(READ_ONCE(sk->sk_sndbuf) >> 1);
limit += 64 * 1024;
This does not take into account that sk->sk_backlog.len
is reset only at the very end of __release_sock().
Both sk->sk_backlog.len and sk->sk_rmem_alloc could reach
sk_rcvbuf in normal conditions.
We should double sk->sk_rcvbuf contribution in the formula
to absorb bubbles in the backlog, which happen more often
for very fast flows.
This change maintains decent protection against abuses.
Fixes: c377411f2494 ("net: sk_add_backlog() take rmem_alloc into account")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240423125620.3309458-1-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e162bed1916ae..e9b1dcf2d463a 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1817,7 +1817,7 @@ int tcp_v4_early_demux(struct sk_buff *skb)
bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
{
- u32 limit, tail_gso_size, tail_gso_segs;
+ u32 tail_gso_size, tail_gso_segs;
struct skb_shared_info *shinfo;
const struct tcphdr *th;
struct tcphdr *thtail;
@@ -1826,6 +1826,7 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
bool fragstolen;
u32 gso_segs;
u32 gso_size;
+ u64 limit;
int delta;
/* In case all data was pulled from skb frags (in __pskb_pull_tail()),
@@ -1922,7 +1923,13 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
__skb_push(skb, hdrlen);
no_coalesce:
- limit = (u32)READ_ONCE(sk->sk_rcvbuf) + (u32)(READ_ONCE(sk->sk_sndbuf) >> 1);
+ /* sk->sk_backlog.len is reset only at the end of __release_sock().
+ * Both sk->sk_backlog.len and sk->sk_rmem_alloc could reach
+ * sk_rcvbuf in normal conditions.
+ */
+ limit = ((u64)READ_ONCE(sk->sk_rcvbuf)) << 1;
+
+ limit += ((u32)READ_ONCE(sk->sk_sndbuf)) >> 1;
/* Only socket owner can try to collapse/prune rx queues
* to reduce memory overhead, so add a little headroom here.
@@ -1930,6 +1937,8 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)
*/
limit += 64 * 1024;
+ limit = min_t(u64, limit, UINT_MAX);
+
if (unlikely(sk_add_backlog(sk, skb, limit))) {
bh_unlock_sock(sk);
__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPBACKLOGDROP);
