cifs: added WARN_ON for all the count decrements

We have a few ref counters srv_count, ses_count and
tc_count which we use for ref counting. Added a WARN_ON
during the decrement of each of these counters to make
sure that they don't go below their minimum values.
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -1295,6 +1295,9 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
 		return;
 	}
 
+	/* srv_count can never go negative */
+	WARN_ON(server->srv_count < 0);
+
 	put_net(cifs_net_ns(server));
 
 	list_del_init(&server->tcp_ses_list);
@@ -1654,6 +1657,9 @@ void cifs_put_smb_ses(struct cifs_ses *ses)
 	}
 	spin_unlock(&cifs_tcp_ses_lock);
 
+	/* ses_count can never go negative */
+	WARN_ON(ses->ses_count < 0);
+
 	spin_lock(&GlobalMid_Lock);
 	if (ses->status == CifsGood)
 		ses->status = CifsExiting;
@@ -2021,6 +2027,9 @@ cifs_put_tcon(struct cifs_tcon *tcon)
 		return;
 	}
 
+	/* tc_count can never go negative */
+	WARN_ON(tcon->tc_count < 0);
+
 	if (tcon->use_witness) {
 		int rc;
 

fs/cifs/smb2ops.c

@@ -2910,6 +2910,8 @@ smb2_get_dfs_refer(const unsigned int xid, struct cifs_ses *ses,
 		/* ipc tcons are not refcounted */
 		spin_lock(&cifs_tcp_ses_lock);
 		tcon->tc_count--;
+		/* tc_count can never go negative */
+		WARN_ON(tcon->tc_count < 0);
 		spin_unlock(&cifs_tcp_ses_lock);
 	}
 	kfree(utf16_path);