SUNRPC: fix races on PipeFS UMOUNT notifications

CPU#0                                   CPU#1
-----------------------------           -----------------------------
rpc_kill_sb
sn->pipefs_sb = NULL                    rpc_release_client
(UMOUNT_EVENT)                          rpc_free_auth
rpc_pipefs_event
rpc_get_client_for_event
!atomic_inc_not_zero(cl_count)
<skip the client>
                                        atomic_inc(cl_count)
                                        rpc_free_client
                                        rpc_clnt_remove_pipedir
                                        <skip client dir removing>

To fix this, this patch does the following:

1) Calls RPC_PIPEFS_UMOUNT notification with sn->pipefs_sb_lock being held.
2) Removes SUNRPC client from the list AFTER pipes destroying.
3) Doesn't hold RPC client on notification: if client in the list, then it
can't be destroyed while sn->pipefs_sb_lock in hold by notification caller.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 2 insertions, 5 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index b827a4b91975..41f180c5a498 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -236,8 +236,6 @@ static struct rpc_clnt *rpc_get_client_for_event(struct net *net, int event)
                         continue;
                 if (rpc_clnt_skip_event(clnt, event))
                         continue;
-                if (atomic_inc_not_zero(&clnt->cl_count) == 0)
-                        continue;
                 spin_unlock(&sn->rpc_client_lock);
                 return clnt;
         }
@@ -254,7 +252,6 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 
         while ((clnt = rpc_get_client_for_event(sb->s_fs_info, event))) {
                 error = __rpc_pipefs_event(clnt, event, sb);
-                rpc_release_client(clnt);
                 if (error)
                         break;
         }
@@ -641,8 +638,8 @@ rpc_free_client(struct rpc_clnt *clnt)
                         rcu_dereference(clnt->cl_xprt)->servername);
         if (clnt->cl_parent != clnt)
                 rpc_release_client(clnt->cl_parent);
-        rpc_unregister_client(clnt);
         rpc_clnt_remove_pipedir(clnt);
+        rpc_unregister_client(clnt);
         rpc_free_iostats(clnt->cl_metrics);
         kfree(clnt->cl_principal);
         clnt->cl_metrics = NULL;
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index e02823bdfe98..4679df5a6d50 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -1166,12 +1166,12 @@ static void rpc_kill_sb(struct super_block *sb)
                 goto out;
         }
         sn->pipefs_sb = NULL;
-        mutex_unlock(&sn->pipefs_sb_lock);
         dprintk("RPC:       sending pipefs UMOUNT notification for net %p%s\n",
                 net, NET_NAME(net));
         blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
                                            RPC_PIPEFS_UMOUNT,
                                            sb);
+        mutex_unlock(&sn->pipefs_sb_lock);
         put_net(net);
 out:
         kill_litter_super(sb);