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

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

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.

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);
 }
 
 /*