diff options
| author | Eric Dumazet <edumazet@google.com> | 2025-09-27 09:28:27 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2025-09-29 18:20:35 -0700 |
| commit | f017c1f768b670bced4464476655b27dfb937e67 (patch) | |
| tree | a894648160be6c0b33cf6acd356053ef93c96264 /net/ipv4/tcp_input.c | |
| parent | d210ee58da1eff63626982ade65632a291aff941 (diff) | |
tcp: use skb->len instead of skb->truesize in tcp_can_ingest()
Some applications are stuck to the 20th century and still use
small SO_RCVBUF values.
After the blamed commit, we can drop packets especially
when using LRO/hw-gro enabled NIC and small MSS (1500) values.
LRO/hw-gro NIC pack multiple segments into pages, allowing
tp->scaling_ratio to be set to a high value.
Whenever the receive queue gets full, we can receive a small packet
filling RWIN, but with a high skb->truesize, because most NIC use 4K page
plus sk_buff metadata even when receiving less than 1500 bytes of payload.
Even if we refine how tp->scaling_ratio is estimated,
we could have an issue at the start of the flow, because
the first round of packets (IW10) will be sent based on
the initial tp->scaling_ratio (1/2)
Relax tcp_can_ingest() to use skb->len instead of skb->truesize,
allowing the peer to use final RWIN, assuming a 'perfect'
scaling_ratio of 1.
Fixes: 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250927092827.2707901-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 79d5252ed6cc..0a2511ce34db 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5086,12 +5086,23 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb); /* Check if this incoming skb can be added to socket receive queues * while satisfying sk->sk_rcvbuf limit. + * + * In theory we should use skb->truesize, but this can cause problems + * when applications use too small SO_RCVBUF values. + * When LRO / hw gro is used, the socket might have a high tp->scaling_ratio, + * allowing RWIN to be close to available space. + * Whenever the receive queue gets full, we can receive a small packet + * filling RWIN, but with a high skb->truesize, because most NIC use 4K page + * plus sk_buff metadata even when receiving less than 1500 bytes of payload. + * + * Note that we use skb->len to decide to accept or drop this packet, + * but sk->sk_rmem_alloc is the sum of all skb->truesize. */ static bool tcp_can_ingest(const struct sock *sk, const struct sk_buff *skb) { - unsigned int new_mem = atomic_read(&sk->sk_rmem_alloc) + skb->truesize; + unsigned int rmem = atomic_read(&sk->sk_rmem_alloc); - return new_mem <= sk->sk_rcvbuf; + return rmem + skb->len <= sk->sk_rcvbuf; } static int tcp_try_rmem_schedule(struct sock *sk, const struct sk_buff *skb, |