SUNRPC: Use RCU to dereference the rpc_clnt.cl_xprt field

A migration event will replace the rpc_xprt used by an rpc_clnt.  To
ensure this can be done safely, all references to cl_xprt must now use
a form of rcu_dereference().

Special care is taken with rpc_peeraddr2str(), which returns a pointer
to memory whose lifetime is the same as the rpc_xprt.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
[ cel: fix lockdep splats and layering violations ]
[ cel: forward ported to 3.4 ]
[ cel: remove rpc_max_reqs(), add rpc_net_ns() ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index f4ccdae6a0cf..7002be11d99f 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -53,6 +53,7 @@
 #include <linux/magic.h>
 #include <linux/parser.h>
 #include <linux/nsproxy.h>
+#include <linux/rcupdate.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -701,8 +702,10 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
                 else
                         seq_puts(m, nfs_infop->nostr);
         }
+        rcu_read_lock();
         seq_printf(m, ",proto=%s",
                    rpc_peeraddr2str(nfss->client, RPC_DISPLAY_NETID));
+        rcu_read_unlock();
         if (version == 4) {
                 if (nfss->port != NFS_PORT)
                         seq_printf(m, ",port=%u", nfss->port);
@@ -751,9 +754,11 @@ static int nfs_show_options(struct seq_file *m, struct dentry *root)
 
         nfs_show_mount_options(m, nfss, 0);
 
+        rcu_read_lock();
         seq_printf(m, ",addr=%s",
                         rpc_peeraddr2str(nfss->nfs_client->cl_rpcclient,
                                                         RPC_DISPLAY_ADDR));
+        rcu_read_unlock();
 
         return 0;
 }