git: 73f56fa542ec - main - tcp lro: use theflowid only when it has hash properties

The branch main has been updated by tuexen:

URL: https://cgit.FreeBSD.org/src/commit/?id=73f56fa542ecf6ea6819c9e17fc60962eeb726d8

commit 73f56fa542ecf6ea6819c9e17fc60962eeb726d8
Author:     Michael Tuexen <tuexen@FreeBSD.org>
AuthorDate: 2025-10-09 12:37:11 +0000
Commit:     Michael Tuexen <tuexen@FreeBSD.org>
CommitDate: 2025-10-09 12:37:11 +0000

    tcp lro: use theflowid only when it has hash properties
    
    When a packet is provided to LRO using tcp_lro_queue_mbuf(), a
    sequence number is computed based on the m_pkthdr.flowid provided
    by he driver. The implicit assumption is that the m_pkthdr.flowid
    has hash properties.
    The recent use of tcp_lro_queue_mbuf() in iflib exposed a bug in at
    least one driver (igc) , which
    * reports always that is uses M_HASHTYPE_OPAQUE.
    * sets in some cases m_pkthdr.flowid not consistently for packets
      belonging to the same TCP connection.
    This results in severe performance problems for the base TCP stack,
    since it handles the packets in the wrong sequence, although they were
    received in the correct sequence.
    To protect against such misbehaving drivers, just take the
    m_pkthdr.flowid only into account, if it has hash properties.
    The performance problems were observed by gallatin@ and analyzed
    together with rrs@.
    
    Reviewed by:            gallatin
    Tested by:              gallatin
    MFC after:              5 Minutes
    Sponsored by:           Netflix, Inc.
    Differential Revision:  https://reviews.freebsd.org/D52989
---
 sys/netinet/tcp_lro.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/sys/netinet/tcp_lro.c b/sys/netinet/tcp_lro.c
index 64efa4bf060f..9b5baf115855 100644
--- a/sys/netinet/tcp_lro.c
+++ b/sys/netinet/tcp_lro.c
@@ -1475,10 +1475,11 @@ tcp_lro_queue_mbuf(struct lro_ctrl *lc, struct mbuf *mb)
  	}
 
 	/* create sequence number */
-	lc->lro_mbuf_data[lc->lro_mbuf_count].seq =
-	    (((uint64_t)M_HASHTYPE_GET(mb)) << 56) |
-	    (((uint64_t)mb->m_pkthdr.flowid) << 24) |
-	    ((uint64_t)lc->lro_mbuf_count);
+	lc->lro_mbuf_data[lc->lro_mbuf_count].seq = lc->lro_mbuf_count;
+	if (M_HASHTYPE_ISHASH(mb))
+		lc->lro_mbuf_data[lc->lro_mbuf_count].seq |=
+		    (((uint64_t)M_HASHTYPE_GET(mb)) << 56) |
+		    (((uint64_t)mb->m_pkthdr.flowid) << 24);
 
 	/* enter mbuf */
 	lc->lro_mbuf_data[lc->lro_mbuf_count].mb = mb;