This is a note to let you know that I've just added the patch titled
udp: gso: do not drop small packets when PMTU reduces
to the 6.13-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:
udp-gso-do-not-drop-small-packets-when-pmtu-reduces.patch
and it can be found in the queue-6.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit c17a8ed80095801f17f2838a82fde2e5ae059651
Author: Yan Zhai <yan@xxxxxxxxxxxxxx>
Date: Fri Jan 31 00:31:39 2025 -0800
udp: gso: do not drop small packets when PMTU reduces
[ Upstream commit 235174b2bed88501fda689c113c55737f99332d8 ]
Commit 4094871db1d6 ("udp: only do GSO if # of segs > 1") avoided GSO
for small packets. But the kernel currently dismisses GSO requests only
after checking MTU/PMTU on gso_size. This means any packets, regardless
of their payload sizes, could be dropped when PMTU becomes smaller than
requested gso_size. We encountered this issue in production and it
caused a reliability problem that new QUIC connection cannot be
established before PMTU cache expired, while non GSO sockets still
worked fine at the same time.
Ideally, do not check any GSO related constraints when payload size is
smaller than requested gso_size, and return EMSGSIZE instead of EINVAL
on MTU/PMTU check failure to be more specific on the error cause.
Fixes: 4094871db1d6 ("udp: only do GSO if # of segs > 1")
Signed-off-by: Yan Zhai <yan@xxxxxxxxxxxxxx>
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c472c9a57cf68..a9bb9ce5438ea 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1141,9 +1141,9 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
const int hlen = skb_network_header_len(skb) +
sizeof(struct udphdr);
- if (hlen + cork->gso_size > cork->fragsize) {
+ if (hlen + min(datalen, cork->gso_size) > cork->fragsize) {
kfree_skb(skb);
- return -EINVAL;
+ return -EMSGSIZE;
}
if (datalen > cork->gso_size * UDP_MAX_SEGMENTS) {
kfree_skb(skb);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index b974116152dd3..3a3c7639d1d61 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1389,9 +1389,9 @@ static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
const int hlen = skb_network_header_len(skb) +
sizeof(struct udphdr);
- if (hlen + cork->gso_size > cork->fragsize) {
+ if (hlen + min(datalen, cork->gso_size) > cork->fragsize) {
kfree_skb(skb);
- return -EINVAL;
+ return -EMSGSIZE;
}
if (datalen > cork->gso_size * UDP_MAX_SEGMENTS) {
kfree_skb(skb);
diff --git a/tools/testing/selftests/net/udpgso.c b/tools/testing/selftests/net/udpgso.c
index 3f2fca02fec53..36ff28af4b190 100644
--- a/tools/testing/selftests/net/udpgso.c
+++ b/tools/testing/selftests/net/udpgso.c
@@ -102,6 +102,19 @@ struct testcase testcases_v4[] = {
.gso_len = CONST_MSS_V4,
.r_num_mss = 1,
},
+ {
+ /* datalen <= MSS < gso_len: will fall back to no GSO */
+ .tlen = CONST_MSS_V4,
+ .gso_len = CONST_MSS_V4 + 1,
+ .r_num_mss = 0,
+ .r_len_last = CONST_MSS_V4,
+ },
+ {
+ /* MSS < datalen < gso_len: fail */
+ .tlen = CONST_MSS_V4 + 1,
+ .gso_len = CONST_MSS_V4 + 2,
+ .tfail = true,
+ },
{
/* send a single MSS + 1B */
.tlen = CONST_MSS_V4 + 1,
@@ -205,6 +218,19 @@ struct testcase testcases_v6[] = {
.gso_len = CONST_MSS_V6,
.r_num_mss = 1,
},
+ {
+ /* datalen <= MSS < gso_len: will fall back to no GSO */
+ .tlen = CONST_MSS_V6,
+ .gso_len = CONST_MSS_V6 + 1,
+ .r_num_mss = 0,
+ .r_len_last = CONST_MSS_V6,
+ },
+ {
+ /* MSS < datalen < gso_len: fail */
+ .tlen = CONST_MSS_V6 + 1,
+ .gso_len = CONST_MSS_V6 + 2,
+ .tfail = true
+ },
{
/* send a single MSS + 1B */
.tlen = CONST_MSS_V6 + 1,
