SUNRPC: allow for upcalls for same uid but different gss service

It's possible to have simultaneous upcalls for the same UIDs but
different GSS service. In that case, we need to allow for the
upcall to gssd to proceed so that not the same context is used
by two different GSS services. Some servers lock the use of context
to the GSS service.
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Cc: stable@vger.kernel.org # v3.9+
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -340,12 +340,14 @@ gss_release_msg(struct gss_upcall_msg *gss_msg)
 }
 
 static struct gss_upcall_msg *
-__gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid)
+__gss_find_upcall(struct rpc_pipe *pipe, kuid_t uid, const struct gss_auth *auth)
 {
 	struct gss_upcall_msg *pos;
 	list_for_each_entry(pos, &pipe->in_downcall, list) {
 		if (!uid_eq(pos->uid, uid))
 			continue;
+		if (auth && pos->auth->service != auth->service)
+			continue;
 		atomic_inc(&pos->count);
 		dprintk("RPC:       %s found msg %p\n", __func__, pos);
 		return pos;
@@ -365,7 +367,7 @@ gss_add_msg(struct gss_upcall_msg *gss_msg)
 	struct gss_upcall_msg *old;
 
 	spin_lock(&pipe->lock);
-	old = __gss_find_upcall(pipe, gss_msg->uid);
+	old = __gss_find_upcall(pipe, gss_msg->uid, gss_msg->auth);
 	if (old == NULL) {
 		atomic_inc(&gss_msg->count);
 		list_add(&gss_msg->list, &pipe->in_downcall);
@@ -714,7 +716,7 @@ gss_pipe_downcall(struct file *filp, const char __user *src, size_t mlen)
 	err = -ENOENT;
 	/* Find a matching upcall */
 	spin_lock(&pipe->lock);
-	gss_msg = __gss_find_upcall(pipe, uid);
+	gss_msg = __gss_find_upcall(pipe, uid, NULL);
 	if (gss_msg == NULL) {
 		spin_unlock(&pipe->lock);
 		goto err_put_ctx;