FAILED: patch "[PATCH] CIFS: Do not miss cancelled OPEN responses" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7b71843fa7028475b052107664cbe120156a2cfc Mon Sep 17 00:00:00 2001
From: Pavel Shilovsky <pshilov@microsoft.com>
Date: Thu, 21 Nov 2019 11:35:14 -0800
Subject: [PATCH] CIFS: Do not miss cancelled OPEN responses

When an OPEN command is cancelled we mark a mid as
cancelled and let the demultiplex thread process it
by closing an open handle. The problem is there is
a race between a system call thread and the demultiplex
thread and there may be a situation when the mid has
been already processed before it is set as cancelled.

Fix this by processing cancelled requests when mids
are being destroyed which means that there is only
one thread referencing a particular mid. Also set
mids as cancelled unconditionally on their state.

Cc: Stable <stable@vger.kernel.org>
Tested-by: Frank Sorenson <sorenson@redhat.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 40b2a173ba0d..a7a026795bc2 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1237,12 +1237,6 @@ cifs_demultiplex_thread(void *p)
 		for (i = 0; i < num_mids; i++) {
 			if (mids[i] != NULL) {
 				mids[i]->resp_buf_size = server->pdu_size;
-				if ((mids[i]->mid_flags & MID_WAIT_CANCELLED) &&
-				    mids[i]->mid_state == MID_RESPONSE_RECEIVED &&
-				    server->ops->handle_cancelled_mid)
-					server->ops->handle_cancelled_mid(
-							mids[i]->resp_buf,
-							server);
 
 				if (!mids[i]->multiRsp || mids[i]->multiEnd)
 					mids[i]->callback(mids[i]);
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index f27842fb9f75..19300e0cf1d6 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -93,8 +93,14 @@ static void _cifs_mid_q_entry_release(struct kref *refcount)
 	__u16 smb_cmd = le16_to_cpu(midEntry->command);
 	unsigned long now;
 	unsigned long roundtrip_time;
-	struct TCP_Server_Info *server = midEntry->server;
 #endif
+	struct TCP_Server_Info *server = midEntry->server;
+
+	if (midEntry->resp_buf && (midEntry->mid_flags & MID_WAIT_CANCELLED) &&
+	    midEntry->mid_state == MID_RESPONSE_RECEIVED &&
+	    server->ops->handle_cancelled_mid)
+		server->ops->handle_cancelled_mid(midEntry->resp_buf, server);
+
 	midEntry->mid_state = MID_FREE;
 	atomic_dec(&midCount);
 	if (midEntry->large_buf)
@@ -1119,8 +1125,8 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
 				 midQ[i]->mid, le16_to_cpu(midQ[i]->command));
 			send_cancel(server, &rqst[i], midQ[i]);
 			spin_lock(&GlobalMid_Lock);
+			midQ[i]->mid_flags |= MID_WAIT_CANCELLED;
 			if (midQ[i]->mid_state == MID_REQUEST_SUBMITTED) {
-				midQ[i]->mid_flags |= MID_WAIT_CANCELLED;
 				midQ[i]->callback = cifs_cancelled_callback;
 				cancelled_mid[i] = true;
 				credits[i].value = 0;