cifs: Don't need state locking in smb2_get_mid_entry()

There's no need to get ->srv_lock or ->ses_lock in smb2_get_mid_entry() as
all that happens of relevance (to the lock) inside the locked sections is
the reading of one status value in each.

Replace the locking with READ_ONCE() and use a switch instead of a chain of
if-statements.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: Tom Talpey <tom@talpey.com>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: dhowells

fs/smb/client/smb2transport.c

@@ -684,43 +684,35 @@ static int
 smb2_get_mid_entry(struct cifs_ses *ses, struct TCP_Server_Info *server,
 		   struct smb2_hdr *shdr, struct mid_q_entry **mid)
 {
-	spin_lock(&server->srv_lock);
-	if (server->tcpStatus == CifsExiting) {
-		spin_unlock(&server->srv_lock);
+	switch (READ_ONCE(server->tcpStatus)) {
+	case CifsExiting:
 		return -ENOENT;
-	}
-
-	if (server->tcpStatus == CifsNeedReconnect) {
-		spin_unlock(&server->srv_lock);
+	case CifsNeedReconnect:
 		cifs_dbg(FYI, "tcp session dead - return to caller to retry\n");
 		return -EAGAIN;
-	}
-
-	if (server->tcpStatus == CifsNeedNegotiate &&
-	   shdr->Command != SMB2_NEGOTIATE) {
-		spin_unlock(&server->srv_lock);
-		return -EAGAIN;
-	}
-	spin_unlock(&server->srv_lock);
-
-	spin_lock(&ses->ses_lock);
-	if (ses->ses_status == SES_NEW) {
-		if ((shdr->Command != SMB2_SESSION_SETUP) &&
-		    (shdr->Command != SMB2_NEGOTIATE)) {
-			spin_unlock(&ses->ses_lock);
+	case CifsNeedNegotiate:
+		if (shdr->Command != SMB2_NEGOTIATE)
 			return -EAGAIN;
-		}
-		/* else ok - we are setting up session */
+		break;
+	default:
+		break;
 	}
 
-	if (ses->ses_status == SES_EXITING) {
-		if (shdr->Command != SMB2_LOGOFF) {
-			spin_unlock(&ses->ses_lock);
+	switch (READ_ONCE(ses->ses_status)) {
+	case SES_NEW:
+		if (shdr->Command != SMB2_SESSION_SETUP &&
+		    shdr->Command != SMB2_NEGOTIATE)
+			return -EAGAIN;
+			/* else ok - we are setting up session */
+		break;
+	case SES_EXITING:
+		if (shdr->Command != SMB2_LOGOFF)
 			return -EAGAIN;
-		}
 		/* else ok - we are shutting down the session */
+		break;
+	default:
+		break;
 	}
-	spin_unlock(&ses->ses_lock);
 
 	*mid = smb2_mid_entry_alloc(shdr, server);
 	if (*mid == NULL)