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, 1 deletions

diff --git a/net/sunrpc/stats.c b/net/sunrpc/stats.c
index 1eb3304bc105..bc2068ee795b 100644
--- a/net/sunrpc/stats.c
+++ b/net/sunrpc/stats.c
@@ -22,6 +22,7 @@
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/svcsock.h>
 #include <linux/sunrpc/metrics.h>
+#include <linux/rcupdate.h>
 
 #include "netns.h"
 
@@ -179,7 +180,7 @@ static void _print_name(struct seq_file *seq, unsigned int op,
 void rpc_print_iostats(struct seq_file *seq, struct rpc_clnt *clnt)
 {
         struct rpc_iostats *stats = clnt->cl_metrics;
-        struct rpc_xprt *xprt = clnt->cl_xprt;
+        struct rpc_xprt *xprt;
         unsigned int op, maxproc = clnt->cl_maxproc;
 
         if (!stats)
@@ -189,8 +190,11 @@ void rpc_print_iostats(struct seq_file *seq, struct rpc_clnt *clnt)
         seq_printf(seq, "p/v: %u/%u (%s)\n",
                         clnt->cl_prog, clnt->cl_vers, clnt->cl_protname);
 
+        rcu_read_lock();
+        xprt = rcu_dereference(clnt->cl_xprt);
         if (xprt)
                 xprt->ops->print_stats(xprt, seq);
+        rcu_read_unlock();
 
         seq_printf(seq, "\tper-op statistics\n");
         for (op = 0; op < maxproc; op++) {