[Devel] [PATCH v2] SUNRPC: check current nsproxy before set of node name on client creation

[Stanislav Kinsbursky]

v2:
1) rpc_clnt_set_nodename() prototype updated.
2) fixed errors in comment.

When child reaper exits, it can destroy mount namespace it belongs to, and if
there are NFS mounts inside, then it will try to umount them. But in this
point current->nsproxy is set to NULL and all namespaces will be destroyed one
by one. I.e. we can't dereference current->nsproxy to obtain uts namespace.

Signed-off-by: Stanislav Kinsbursky <skinsbursky at parallels.com>
---
 net/sunrpc/clnt.c |   16 +++++++++++++---
 1 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 9a9676e..8fbcbc8 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -277,8 +277,18 @@ void rpc_clients_notifier_unregister(void)
 	return rpc_pipefs_notifier_unregister(&rpc_clients_block);
 }
 
-static void rpc_clnt_set_nodename(struct rpc_clnt *clnt, const char *nodename)
+static void rpc_clnt_set_nodename(struct rpc_clnt *clnt)
 {
+	const char *nodename;
+
+	/*
+	 * We have to protect against dying child reaper, which has released
+	 * its nsproxy already and is trying to destroy mount namespace.
+	 */
+	if (current->nsproxy == NULL)
+		return;
+
+	nodename = utsname()->nodename;
 	clnt->cl_nodelen = strlen(nodename);
 	if (clnt->cl_nodelen > UNX_MAXNODENAME)
 		clnt->cl_nodelen = UNX_MAXNODENAME;
@@ -365,7 +375,7 @@ static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args, stru
 	}
 
 	/* save the nodename */
-	rpc_clnt_set_nodename(clnt, utsname()->nodename);
+	rpc_clnt_set_nodename(clnt);
 	rpc_register_client(clnt);
 	return clnt;
 
@@ -524,7 +534,7 @@ rpc_clone_client(struct rpc_clnt *clnt)
 	err = rpc_setup_pipedir(new, clnt->cl_program->pipe_dir_name);
 	if (err != 0)
 		goto out_no_path;
-	rpc_clnt_set_nodename(new, utsname()->nodename);
+	rpc_clnt_set_nodename(new);
 	if (new->cl_auth)
 		atomic_inc(&new->cl_auth->au_count);
 	atomic_inc(&clnt->cl_count);