Messages in this thread Patch in this message | | | From | NeilBrown <> | Date | Fri, 20 Oct 2006 11:52:44 +1000 | Subject | [PATCH] knfsd: Fix race that can disable NFS server. |
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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 <neilb@suse.de>
### 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; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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