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authorEric Dumazet <edumazet@google.com>2024-04-23 12:56:20 +0000
committerJakub Kicinski <kuba@kernel.org>2024-04-25 12:15:02 -0700
commitec00ed472bdb7d0af840da68c8c11bff9f4d9caa (patch)
tree7b9bb64d8735b8f6f94c6b211959765da79f2f46
parente6be197f23c5cf15fb4a5acac213b77f80e8cf96 (diff)
tcp: avoid premature drops in tcp_add_backlog()
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@google.com> Link: https://lore.kernel.org/r/20240423125620.3309458-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
-rw-r--r--net/ipv4/tcp_ipv4.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 88c83ac42129..e06f0cd04f7e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1995,7 +1995,7 @@ int tcp_v4_early_demux(struct sk_buff *skb)
bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb,
enum skb_drop_reason *reason)
{
- 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;
@@ -2004,6 +2004,7 @@ 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()),
@@ -2099,7 +2100,13 @@ 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.
@@ -2107,6 +2114,8 @@ no_coalesce:
*/
limit += 64 * 1024;
+ limit = min_t(u64, limit, UINT_MAX);
+
if (unlikely(sk_add_backlog(sk, skb, limit))) {
bh_unlock_sock(sk);
*reason = SKB_DROP_REASON_SOCKET_BACKLOG;