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, 17 insertions, 8 deletions

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index c1111a37dc14..bae959e294cd 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -1037,19 +1037,28 @@ static void nfs4_clear_state_manager_bit(struct nfs_client *clp)
 void nfs4_schedule_state_manager(struct nfs_client *clp)
 {
         struct task_struct *task;
+        char buf[INET6_ADDRSTRLEN + sizeof("-manager") + 1];
 
         if (test_and_set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state) != 0)
                 return;
         __module_get(THIS_MODULE);
         atomic_inc(&clp->cl_count);
-        task = kthread_run(nfs4_run_state_manager, clp, "%s-manager",
-                                rpc_peeraddr2str(clp->cl_rpcclient,
-                                                        RPC_DISPLAY_ADDR));
-        if (!IS_ERR(task))
-                return;
-        nfs4_clear_state_manager_bit(clp);
-        nfs_put_client(clp);
-        module_put(THIS_MODULE);
+
+        /* The rcu_read_lock() is not strictly necessary, as the state
+         * manager is the only thread that ever changes the rpc_xprt
+         * after it's initialized.  At this point, we're single threaded. */
+        rcu_read_lock();
+        snprintf(buf, sizeof(buf), "%s-manager",
+                        rpc_peeraddr2str(clp->cl_rpcclient, RPC_DISPLAY_ADDR));
+        rcu_read_unlock();
+        task = kthread_run(nfs4_run_state_manager, clp, buf);
+        if (IS_ERR(task)) {
+                printk(KERN_ERR "%s: kthread_run: %ld\n",
+                        __func__, PTR_ERR(task));
+                nfs4_clear_state_manager_bit(clp);
+                nfs_put_client(clp);
+                module_put(THIS_MODULE);
+        }
 }
 
 /*