* Re: [PATCH] knfsd: Fix race that can disable NFS server.
2006-10-20 1:52 ` [PATCH] knfsd: Fix race that can disable NFS server NeilBrown
@ 2006-11-05 7:49 ` Adrian Bunk
0 siblings, 0 replies; 2+ messages in thread
From: Adrian Bunk @ 2006-11-05 7:49 UTC (permalink / raw)
To: NeilBrown; +Cc: Andrew Morton, nfs
On Fri, Oct 20, 2006 at 11:52:44AM +1000, NeilBrown wrote:
> 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.
Thanks, applied to 2.6.16.
> ### 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;
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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