nfsd: don't alloc under spinlock in rpc_parse_scope_id

Dan Carpenter says:

The patch d20c11d86d8f: "nfsd: Protect session creation and client
confirm using client_lock" from Jul 30, 2014, leads to the following
Smatch static checker warning:

net/sunrpc/addr.c:178 rpc_parse_scope_id()
warn: sleeping in atomic context

Reported-by: Dan Carpenter <[e-mail]>
Fixes: d20c11d86d8f ("nfsd: Protect session creation and client...")
Signed-off-by: J. Bruce Fields <[e-mail]>

net/sunrpc/addr.c

···
 			      const size_t buflen, const char *delim,
 			      struct sockaddr_in6 *sin6)
 {
-	char *p;
+	char p[IPV6_SCOPE_ID_LEN + 1];
 	size_t len;
+	u32 scope_id = 0;
+	struct net_device *dev;
 
 	if ((buf + buflen) == delim)
 		return 1;
···
 		return 0;
 
 	len = (buf + buflen) - delim - 1;
-	p = kmemdup_nul(delim + 1, len, GFP_KERNEL);
-	if (p) {
-		u32 scope_id = 0;
-		struct net_device *dev;
+	if (len > IPV6_SCOPE_ID_LEN)
+		return 0;
 
-		dev = dev_get_by_name(net, p);
-		if (dev != NULL) {
-			scope_id = dev->ifindex;
-			dev_put(dev);
-		} else {
-			if (kstrtou32(p, 10, &scope_id) != 0) {
-				kfree(p);
-				return 0;
-			}
-		}
+	memcpy(p, delim + 1, len);
+	p[len] = 0;
 
-		kfree(p);
-
-		sin6->sin6_scope_id = scope_id;
-		return 1;
+	dev = dev_get_by_name(net, p);
+	if (dev != NULL) {
+		scope_id = dev->ifindex;
+		dev_put(dev);
+	} else {
+		if (kstrtou32(p, 10, &scope_id) != 0)
+			return 0;
 	}
 
-	return 0;
+	sin6->sin6_scope_id = scope_id;
+	return 1;
 }
 
 static size_t rpc_pton6(struct net *net, const char *buf, const size_t buflen,