cifs: missing lock when updating session status

Coverity noted a place where we were not grabbing
the ses_lock when setting (and checking) ses_status.

Addresses-Coverity: 1536833 ("Data race condition (MISSING_LOCK)")
Reviewed-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Reviewed-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/cifs/connect.c

@@ -1916,18 +1916,22 @@ void cifs_put_smb_ses(struct cifs_ses *ses)
 	/* ses_count can never go negative */
 	WARN_ON(ses->ses_count < 0);
 
+	spin_lock(&ses->ses_lock);
 	if (ses->ses_status == SES_GOOD)
 		ses->ses_status = SES_EXITING;
 
-	cifs_free_ipc(ses);
-
 	if (ses->ses_status == SES_EXITING && server->ops->logoff) {
+		spin_unlock(&ses->ses_lock);
+		cifs_free_ipc(ses);
 		xid = get_xid();
 		rc = server->ops->logoff(xid, ses);
 		if (rc)
 			cifs_server_dbg(VFS, "%s: Session Logoff failure rc=%d\n",
 				__func__, rc);
 		_free_xid(xid);
+	} else {
+		spin_unlock(&ses->ses_lock);
+		cifs_free_ipc(ses);
 	}
 
 	spin_lock(&cifs_tcp_ses_lock);