path: root/net/ipv4/tcp_ipv4.c
diff options
authorEric Dumazet <edumazet@google.com>2018-02-13 06:14:12 -0800
committerDavid S. Miller <davem@davemloft.net>2018-02-14 14:21:45 -0500
commite0f9759f530bf789e984961dce79f525b151ecf3 (patch)
tree8f384615d4648a8fc46c70db06dd9021a0a480b4 /net/ipv4/tcp_ipv4.c
parentMerge branch 'net-dev-Make-protocol-ptr-dependent-on-CONFIG' (diff)
tcp: try to keep packet if SYN_RCV race is lost
배석진 reported that in some situations, packets for a given 5-tuple end up being processed by different CPUS. This involves RPS, and fragmentation. 배석진 is seeing packet drops when a SYN_RECV request socket is moved into ESTABLISH state. Other states are protected by socket lock. This is caused by a CPU losing the race, and simply not caring enough. Since this seems to occur frequently, we can do better and perform a second lookup. Note that all needed memory barriers are already in the existing code, thanks to the spin_lock()/spin_unlock() pair in inet_ehash_insert() and reqsk_put(). The second lookup must find the new socket, unless it has already been accepted and closed by another cpu. Note that the fragmentation could be avoided in the first place by use of a correct TCP MSS option in the SYN{ACK} packet, but this does not mean we can not be more robust. Many thanks to 배석진 for a very detailed analysis. Reported-by: 배석진 <soukjin.bae@samsung.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_ipv4.c')
1 files changed, 12 insertions, 1 deletions
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ac16795486ea..f3e52bc98980 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1672,6 +1672,7 @@ process:
if (sk->sk_state == TCP_NEW_SYN_RECV) {
struct request_sock *req = inet_reqsk(sk);
+ bool req_stolen = false;
struct sock *nsk;
sk = req->rsk_listener;
@@ -1694,10 +1695,20 @@ process:
th = (const struct tcphdr *)skb->data;
iph = ip_hdr(skb);
tcp_v4_fill_cb(skb, iph, th);
- nsk = tcp_check_req(sk, skb, req, false);
+ nsk = tcp_check_req(sk, skb, req, false, &req_stolen);
if (!nsk) {
+ if (req_stolen) {
+ /* Another cpu got exclusive access to req
+ * and created a full blown socket.
+ * Try to feed this packet to this socket
+ * instead of discarding it.
+ */
+ tcp_v4_restore_cb(skb);
+ sock_put(sk);
+ goto lookup;
+ }
goto discard_and_relse;
if (nsk == sk) {