[CIFS] Reduce number of socket retries in large write path

CIFS in some heavy stress conditions cifs could get EAGAIN
repeatedly in smb_send2 which led to repeated retries and eventually
failure of large writes which could lead to data corruption.

There are three changes that were suggested by various network
developers:

1) convert cifs from non-blocking to blocking tcp sendmsg
(we left in the retry on failure)
2) change cifs to not set sendbuf and rcvbuf size for the socket
(let tcp autotune the buffer sizes since that works much better
in the TCP stack now)
3) if we have a partial frame sent in smb_send2, mark the tcp
session as invalid (close the socket and reconnect) so we do
not corrupt the remaining part of the SMB with the beginning
of the next SMB.

This does not appear to hurt performance measurably and has
been run in various scenarios, but it definately removes
a corruption that we were seeing in some high stress
test cases.

Acked-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index 8f528ea..8855331 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -4,7 +4,11 @@ Various fixes to make delete of open files behavior more predictable
 (when delete of an open file fails we mark the file as "delete-on-close"
 in a way that more servers accept, but only if we can first rename the
 file to a temporary name).  Add experimental support for more safely
-handling fcntl(F_SETLEASE).
+handling fcntl(F_SETLEASE).  Convert cifs to using blocking tcp
+sends, and also let tcp autotune the socket send and receive buffers.
+This reduces the number of EAGAIN errors returned by TCP/IP in
+high stress workloads (and the number of retries on socket writes
+when sending large SMBWriteX requests).
 
 Version 1.54
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