[RFC PATCH v2] SUNRPC: protect service sockets lists during per-net shutdown

Stanislav Kinsbursky
2012-05-21T08:52:04Z

v2: destruction of currently processing transport added:
1) Added marking of currently processing transports with XPT_CLOSE on per-net
shutdown. These transports will be destroy in svc_xprt_enqueue() (instead of
enqueueing).
2) newly created temporary transport in svc_recv() will be destroyed, if it's
"parent" was marked wof currently processing transports ith XPT_CLOSE.
3) spin_lock(&serv->sv_lock) was replaced by spin_lock_bh() in
svc_close_net(&serv->sv_lock).

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 | 56 ++++++++++++++++++++++++++++++++++++++++++++++---
1 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 37a1f66..947d3cb 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -320,6 +320,7 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
struct svc_pool *pool;
struct svc_rqst *rqstp;
int cpu;
+ int destroy = 0;

if (!svc_xprt_has_something_to_do(xprt))
return;
@@ -338,6 +339,17 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)

pool->sp_stats.packets++;

+ /*
+ * Check transport close flag. It could be marked as closed on per-net
+ * service shutdown.
+ */
+ if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
+ /* Don't enqueue transport if it has to be destroyed. */
+ dprintk("svc: transport %p have to be closed\n", xprt);
+ destroy++;
+ goto out_unlock;
+ }
+
/* Mark transport as busy. It will remain in this state until
* the provider calls svc_xprt_received. We update XPT_BUSY
* atomically because it also guards against trying to enqueue
@@ -374,6 +386,8 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)

out_unlock:
spin_unlock_bh(&pool->sp_lock);
+ if (destroy)
+ svc_delete_xprt(xprt);
}
EXPORT_SYMBOL_GPL(svc_xprt_enqueue);

@@ -717,6 +731,13 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
__module_get(newxpt->xpt_class->xcl_owner);
svc_check_conn_limits(xprt->xpt_server);
spin_lock_bh(&serv->sv_lock);
+ if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
+ dprintk("svc_recv: found XPT_CLOSE on listener\n");
+ set_bit(XPT_DETACHED, &newxpt->xpt_flags);
+ spin_unlock_bh(&pool->sp_lock);
+ svc_delete_xprt(newxpt);
+ goto out_closed;
+ }
set_bit(XPT_TEMP, &newxpt->xpt_flags);
list_add(&newxpt->xpt_list, &serv->sv_tempsocks);
serv->sv_tmpcnt++;
@@ -742,6 +763,7 @@ int svc_recv(struct svc_rqst *rqstp, long timeout)
len = xprt->xpt_ops->xpo_recvfrom(rqstp);
dprintk("svc: got len=%d\n", len);
}
+out_closed:
svc_xprt_received(xprt);

/* No data, incomplete (TCP) read, or accept() */
@@ -939,6 +961,7 @@ static void svc_clear_pools(struct svc_serv *serv, struct net *net)
struct svc_pool *pool;
struct svc_xprt *xprt;
struct svc_xprt *tmp;
+ struct svc_rqst *rqstp;
int i;

for (i = 0; i < serv->sv_nrpools; i++) {
@@ -950,11 +973,16 @@ static void svc_clear_pools(struct svc_serv *serv, struct net *net)
continue;
list_del_init(&xprt->xpt_ready);
}
+ list_for_each_entry(rqstp, &pool->sp_all_threads, rq_all) {
+ if (rqstp->rq_xprt && rqstp->rq_xprt->xpt_net == net)
+ set_bit(XPT_CLOSE, &rqstp->rq_xprt->xpt_flags);
+ }
spin_unlock_bh(&pool->sp_lock);
}
}

-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 +990,8 @@ 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 +999,15 @@ 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, *tmp;
+ LIST_HEAD(kill_list);
+
+ /*
+ * Protect the lists, since they can be by tasks with different network
+ * namespace contexts.
+ */
+ spin_lock_bh(&serv->sv_lock);
+
svc_close_list(&serv->sv_tempsocks, net);
svc_close_list(&serv->sv_permsocks, net);

@@ -979,8 +1017,18 @@ void svc_close_net(struct svc_serv *serv, struct net *net)
* svc_xprt_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_bh(&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_safe(xprt, tmp, &kill_list, xpt_list)
+ svc_delete_xprt(xprt);
}

/*