From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946782AbWJTBw6 (ORCPT ); Thu, 19 Oct 2006 21:52:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1946784AbWJTBw6 (ORCPT ); Thu, 19 Oct 2006 21:52:58 -0400 Received: from ns2.suse.de ([195.135.220.15]:10638 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S1946782AbWJTBw5 (ORCPT ); Thu, 19 Oct 2006 21:52:57 -0400 From: NeilBrown To: Andrew Morton Date: Fri, 20 Oct 2006 11:52:44 +1000 Message-Id: <1061020015244.26756@suse.de> X-face: [Gw_3E*Gng}4rRrKRYotwlE?.2|**#s9D Subject: [PATCH] knfsd: Fix race that can disable NFS server. References: <20061020114959.26698.patches@notabene> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This patch is suitable for just about any 2.6 kernel. It should go in 2.6.19 and 2.6.18.2 and possible even the .17 and .16 stable series. ### Comments for Changeset This is a long standing bug that seems to have only recently become apparent, presumably due to increasing use of NFS over TCP - many distros seem to be making it the default. The SK_CONN bit gets set when a listening socket may be ready for an accept, just as SK_DATA is set when data may be available. It is entirely possible for svc_tcp_accept to be called with neither of these set. It doesn't happen often but there is a small race in svc_sock_enqueue as SK_CONN and SK_DATA are tested outside the spin_lock. They could be cleared immediately after the test and before the lock is gained. This normally shouldn't be a problem. The sockets are non-blocking so trying to read() or accept() when ther is nothing to do is not a problem. However: svc_tcp_recvfrom makes the decision "Should I accept() or should I read()" based on whether SK_CONN is set or not. This usually works but is not safe. The decision should be based on whether it is a TCP_LISTEN socket or a TCP_CONNECTED socket. Signed-off-by: Neil Brown ### Diffstat output ./net/sunrpc/svcsock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff .prev/net/sunrpc/svcsock.c ./net/sunrpc/svcsock.c --- .prev/net/sunrpc/svcsock.c 2006-10-20 11:49:18.000000000 +1000 +++ ./net/sunrpc/svcsock.c 2006-10-20 11:49:47.000000000 +1000 @@ -1002,7 +1002,7 @@ svc_tcp_recvfrom(struct svc_rqst *rqstp) return 0; } - if (test_bit(SK_CONN, &svsk->sk_flags)) { + if (svsk->sk_sk->sk_state == TCP_LISTEN) { svc_tcp_accept(svsk); svc_sock_received(svsk); return 0;