Patch "cifs: Limit the overall credit acquired" has been added to the 4.8-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    cifs: Limit the overall credit acquired

to the 4.8-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:
     cifs-limit-the-overall-credit-acquired.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 7d414f396c91a3382e51cf628c1cf0709ad0188b Mon Sep 17 00:00:00 2001
From: Ross Lagerwall <ross.lagerwall@citrix.com>
Date: Tue, 20 Sep 2016 13:37:13 +0100
Subject: cifs: Limit the overall credit acquired

From: Ross Lagerwall <ross.lagerwall@citrix.com>

commit 7d414f396c91a3382e51cf628c1cf0709ad0188b upstream.

The kernel client requests 2 credits for many operations even though
they only use 1 credit (presumably to build up a buffer of credit).
Some servers seem to give the client as much credit as is requested.  In
this case, the amount of credit the client has continues increasing to
the point where (server->credits * MAX_BUFFER_SIZE) overflows in
smb2_wait_mtu_credits().

Fix this by throttling the credit requests if an set limit is reached.
For async requests where the credit charge may be > 1, request as much
credit as what is charged.
The limit is chosen somewhat arbitrarily. The Windows client
defaults to 128 credits, the Windows server allows clients up to
512 credits (or 8192 for Windows 2016), and the NetApp server
(and at least one other) does not limit clients at all.
Choose a high enough value such that the client shouldn't limit
performance.

This behavior was seen with a NetApp filer (NetApp Release 9.0RC2).

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/cifs/smb2glob.h |   10 ++++++++++
 fs/cifs/smb2pdu.c  |   18 +++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

--- a/fs/cifs/smb2glob.h
+++ b/fs/cifs/smb2glob.h
@@ -61,4 +61,14 @@
 /* Maximum buffer size value we can send with 1 credit */
 #define SMB2_MAX_BUFFER_SIZE 65536
 
+/*
+ * Maximum number of credits to keep available.
+ * This value is chosen somewhat arbitrarily. The Windows client
+ * defaults to 128 credits, the Windows server allows clients up to
+ * 512 credits, and the NetApp server does not limit clients at all.
+ * Choose a high enough value such that the client shouldn't limit
+ * performance.
+ */
+#define SMB2_MAX_CREDITS_AVAILABLE 32000
+
 #endif	/* _SMB2_GLOB_H */
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -100,7 +100,21 @@ smb2_hdr_assemble(struct smb2_hdr *hdr,
 	hdr->ProtocolId = SMB2_PROTO_NUMBER;
 	hdr->StructureSize = cpu_to_le16(64);
 	hdr->Command = smb2_cmd;
-	hdr->CreditRequest = cpu_to_le16(2); /* BB make this dynamic */
+	if (tcon && tcon->ses && tcon->ses->server) {
+		struct TCP_Server_Info *server = tcon->ses->server;
+
+		spin_lock(&server->req_lock);
+		/* Request up to 2 credits but don't go over the limit. */
+		if (server->credits >= SMB2_MAX_CREDITS_AVAILABLE)
+			hdr->CreditRequest = cpu_to_le16(0);
+		else
+			hdr->CreditRequest = cpu_to_le16(
+				min_t(int, SMB2_MAX_CREDITS_AVAILABLE -
+						server->credits, 2));
+		spin_unlock(&server->req_lock);
+	} else {
+		hdr->CreditRequest = cpu_to_le16(2);
+	}
 	hdr->ProcessId = cpu_to_le32((__u16)current->tgid);
 
 	if (!tcon)
@@ -2057,6 +2071,7 @@ smb2_async_readv(struct cifs_readdata *r
 	if (rdata->credits) {
 		buf->CreditCharge = cpu_to_le16(DIV_ROUND_UP(rdata->bytes,
 						SMB2_MAX_BUFFER_SIZE));
+		buf->CreditRequest = buf->CreditCharge;
 		spin_lock(&server->req_lock);
 		server->credits += rdata->credits -
 						le16_to_cpu(buf->CreditCharge);
@@ -2243,6 +2258,7 @@ smb2_async_writev(struct cifs_writedata
 	if (wdata->credits) {
 		req->hdr.CreditCharge = cpu_to_le16(DIV_ROUND_UP(wdata->bytes,
 						    SMB2_MAX_BUFFER_SIZE));
+		req->hdr.CreditRequest = req->hdr.CreditCharge;
 		spin_lock(&server->req_lock);
 		server->credits += wdata->credits -
 					le16_to_cpu(req->hdr.CreditCharge);


Patches currently in stable-queue which might be from ross.lagerwall@citrix.com are

queue-4.8/cifs-limit-the-overall-credit-acquired.patch