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, 10 insertions, 3 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 6c8e170e2e6b..671510cc14c0 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -3833,6 +3833,7 @@ int nfs4_proc_setclientid(struct nfs_client *clp, u32 program,
         *p = htonl((u32)clp->cl_boot_time.tv_nsec);
 
         for(;;) {
+                rcu_read_lock();
                 setclientid.sc_name_len = scnprintf(setclientid.sc_name,
                                 sizeof(setclientid.sc_name), "%s/%s %s %s %u",
                                 clp->cl_ipaddr,
@@ -3849,6 +3850,7 @@ int nfs4_proc_setclientid(struct nfs_client *clp, u32 program,
                 setclientid.sc_uaddr_len = scnprintf(setclientid.sc_uaddr,
                                 sizeof(setclientid.sc_uaddr), "%s.%u.%u",
                                 clp->cl_ipaddr, port >> 8, port & 255);
+                rcu_read_unlock();
 
                 status = rpc_call_sync(clp->cl_rpcclient, &msg, RPC_TASK_TIMEOUT);
                 if (status != -NFS4ERR_CLID_INUSE)
@@ -5244,11 +5246,16 @@ struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp)
 
 void nfs4_destroy_session(struct nfs4_session *session)
 {
+        struct rpc_xprt *xprt;
+
         nfs4_proc_destroy_session(session);
+
+        rcu_read_lock();
+        xprt = rcu_dereference(session->clp->cl_rpcclient->cl_xprt);
+        rcu_read_unlock();
         dprintk("%s Destroy backchannel for xprt %p\n",
-                __func__, session->clp->cl_rpcclient->cl_xprt);
-        xprt_destroy_backchannel(session->clp->cl_rpcclient->cl_xprt,
-                                NFS41_BC_MIN_CALLBACKS);
+                __func__, xprt);
+        xprt_destroy_backchannel(xprt, NFS41_BC_MIN_CALLBACKS);
         nfs4_destroy_slot_tables(session);
         kfree(session);
 }