SUNRPC: add WARN_ON_ONCE for potential deadlock

rpc_shutdown_client should never be called from a workqueue context.
If it is, it could deadlock looping forever trying to kill tasks that are
assigned to the same kworker thread (and will never run rpc_exit_task).

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index cdc7564b4512..dd2532c10324 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -607,6 +607,13 @@ EXPORT_SYMBOL_GPL(rpc_killall_tasks);
  */
 void rpc_shutdown_client(struct rpc_clnt *clnt)
 {
+        /*
+         * To avoid deadlock, never call rpc_shutdown_client from a
+         * workqueue context!
+         */
+        WARN_ON_ONCE(current->flags & PF_WQ_WORKER);
+        might_sleep();
+
         dprintk_rcu("RPC:       shutting down %s client for %s\n",
                         clnt->cl_protname,
                         rcu_dereference(clnt->cl_xprt)->servername);