Re: [RFC PATCH] SUNRPC: protect service sockets lists during per-net shutdown

J. Bruce Fields
2012-05-16T16:34:36Z

On Fri, May 11, 2012 at 03:41:56PM +0400, Stanislav Kinsbursky wrote:
> Service sv_tempsocks and sv_permsocks lists are accessible by tasks with
> different network namespaces, and thus per-net service destruction must be
> protected.
> These lists are protected by service sv_lock. So lets wrap list munipulations
> with this lock and move tranports destruction outside wrapped area to prevent
> deadlocks.

The comment I originally quoted is still wrong now:

/*
* The set of xprts (contained in the sv_tempsocks and
* sv_permsocks lists) is now constant, since it is modified
* only by accepting new sockets (done by service threads in
* svc_recv) or aging old ones (done by sv_temptimer), or
* configuration changes (excluded by whatever locking the
* caller is using--nfsd_mutex in the case of nfsd). So it's
* safe to traverse those lists and shut everything down:
*/

And I think that's still a problem.

A server thread could be running svc_recv(), handling a new connection
on a listening socket in the network namespace that we're shutting down.

And then I'm not sure exactly what happens, but it doesn't look right.
At best we end up adding a connection from the new network namespace
after we thought we'd got rid of them all. More likely we crash
somewhere.

--b.

>
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
> ---
> net/sunrpc/svc_xprt.c | 29 +++++++++++++++++++++++++----
> 1 files changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 8195c6a..233f993 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -954,7 +954,8 @@ static void svc_clear_pools(struct svc_serv *serv, struct net *net)
> }
> }
>
> -static void svc_clear_list(struct list_head *xprt_list, struct net *net)
> +static void svc_clear_list(struct list_head *xprt_list, struct net *net,
> + struct list_head *kill_list)
> {
> struct svc_xprt *xprt;
> struct svc_xprt *tmp;
> @@ -962,7 +963,8 @@ static void svc_clear_list(struct list_head *xprt_list, struct net *net)
> list_for_each_entry_safe(xprt, tmp, xprt_list, xpt_list) {
> if (xprt->xpt_net != net)
> continue;
> - svc_delete_xprt(xprt);
> + list_move(&xprt->xpt_list, kill_list);
> + set_bit(XPT_DETACHED, &xprt->xpt_flags);
> }
> list_for_each_entry(xprt, xprt_list, xpt_list)
> BUG_ON(xprt->xpt_net == net);
> @@ -970,6 +972,15 @@ static void svc_clear_list(struct list_head *xprt_list, struct net *net)
>
> void svc_close_net(struct svc_serv *serv, struct net *net)
> {
> + struct svc_xprt *xprt;
> + LIST_HEAD(kill_list);
> +
> + /*
> + * Protect the lists, since they can be by tasks with different network
> + * namespace contexts.
> + */
> + spin_lock(&serv->sv_lock);
> +
> svc_close_list(&serv->sv_tempsocks, net);
> svc_close_list(&serv->sv_permsocks, net);
>
> @@ -979,8 +990,18 @@ void svc_close_net(struct svc_serv *serv, struct net *net)
> * svc_enqueue will not add new entries without taking the
> * sp_lock and checking XPT_BUSY.
> */
> - svc_clear_list(&serv->sv_tempsocks, net);
> - svc_clear_list(&serv->sv_permsocks, net);
> + svc_clear_list(&serv->sv_tempsocks, net, &kill_list);
> + svc_clear_list(&serv->sv_permsocks, net, &kill_list);
> +
> + spin_unlock(&serv->sv_lock);
> +
> + /*
> + * Destroy collected transports.
> + * Note: tranports has been marked as XPT_DETACHED on svc_clear_list(),
> + * so no need to protect againt list_del() in svc_delete_xprt().
> + */
> + list_for_each_entry(xprt, &kill_list, xpt_list)
> + svc_delete_xprt(xprt);
> }
>
> /*
>