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Bug #13475
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TCP sends fragmented IP when LSO is enabled
Start date:
Due date:
% Done:
0%
Estimated time:
Difficulty:
Medium
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Gerrit CR:
External Bug:
Description
Situation:
- tcp connection was closed
- there is more than one mss unsent
- LSO is enabled
In tcp_send() the calculation of bytes to send is done under the assumption that LSO will be used. A value higher than mss is set for lso_usable. Later this 'if' is taken, because we are at the end of the data stream:
if (tcp->tcp_valid_bits != 0 &&
(tcp->tcp_valid_bits != TCP_FSS_VALID ||
((*snxt + len) == tcp->tcp_fss))) {
This causes data with len > mss being sent without LSO setup and due to this with IP fragmentation. Beside the general wish to avoid IP fragmentation this conflicted with IP filter: The additional fragments were dropped and retransmission occurred.
I can imagine two fixes:
- the easy one: don't do LSO if any of the VALID bits is set
- more complicated: with TCP_FSS_VALID don't send the complete unsent data with LSO but leave data <=mss for the next loop, which will then automaticaly be without LSO
Updated by David Hanisch almost 3 years ago
This how a fix could look like.
The easy one:
diff --git a/usr/src/uts/common/inet/tcp/tcp_output.c b/usr/src/uts/common/inet/tcp/tcp_output.c
index 115842e5e1e0..3fb1eb53fd1f 100644
--- a/usr/src/uts/common/inet/tcp/tcp_output.c
+++ b/usr/src/uts/common/inet/tcp/tcp_output.c
@@ -1783,7 +1783,7 @@ tcp_send(tcp_t *tcp, const int mss, const int total_hdr_len,
* enough available data to initiate LSO transmission in the for(){}
* loops.
*/
- if (tcp->tcp_lso && (tcp->tcp_valid_bits & ~TCP_FSS_VALID) == 0)
+ if (tcp->tcp_lso && tcp->tcp_valid_bits == 0)
do_lso_send = B_TRUE;
for (;;) {
A bit more complicated:
diff --git a/usr/src/uts/common/inet/tcp/tcp_output.c b/usr/src/uts/common/inet/tcp/tcp_output.c
index 115842e5e1e0..998fd76aee87 100644
--- a/usr/src/uts/common/inet/tcp/tcp_output.c
+++ b/usr/src/uts/common/inet/tcp/tcp_output.c
@@ -1803,8 +1803,17 @@ tcp_send(tcp_t *tcp, const int mss, const int total_hdr_len,
* Determine whether or not it's possible to do LSO,
* and if so, how much data we can send.
*/
- if ((*usable - 1) / mss >= 1) {
- lso_usable = MIN(tcp->tcp_lso_max, *usable);
+ lso_usable = MIN(tcp->tcp_lso_max, *usable);
+ if ((tcp->tcp_valid_bits & TCP_FSS_VALID) &&
+ (*snxt + lso_usable) == tcp->tcp_fss) {
+ /*
+ * we must leave some data to be sent not LSO
+ * through the tcp_xmit_mp() (see below)
+ */
+ int remain = lso_usable % mss;
+ lso_usable -= remain ? remain : mss;
+ }
+ if ((lso_usable - 1) / mss >= 1) {
num_lso_seg = lso_usable / mss;
if (lso_usable % mss) {
num_lso_seg++;
Updated by Marcel Telka over 2 years ago
- Subject changed from TCP sends segmented IP when LSO is enabled to TCP sends fragmented IP when LSO is enabled
- Description updated (diff)
Updated by Marcel Telka over 2 years ago
- Category set to networking
- Status changed from New to In Progress
- Assignee set to Marcel Telka
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