SUNRPC: Optimise rpciod_up()

Instead of taking the mutex every time we just need to increment/decrement
rpciod_users, we can optmise by using atomic_inc_not_zero and
atomic_dec_and_test.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 21 insertions, 28 deletions

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index d95fe4e40eb4..f6eed4d4e5dd 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -58,7 +58,7 @@ static DECLARE_WAIT_QUEUE_HEAD(client_kill_wait);
  * rpciod-related stuff
  */
 static DEFINE_MUTEX(rpciod_mutex);
-static unsigned int             rpciod_users;
+static atomic_t rpciod_users = ATOMIC_INIT(0);
 struct workqueue_struct *rpciod_workqueue;
 
 /*
@@ -1047,28 +1047,27 @@ rpciod_up(void)
         struct workqueue_struct *wq;
         int error = 0;
 
+        if (atomic_inc_not_zero(&rpciod_users))
+                return 0;
+
         mutex_lock(&rpciod_mutex);
-        dprintk("RPC:       rpciod_up: users %u\n", rpciod_users);
-        rpciod_users++;
-        if (rpciod_workqueue)
-                goto out;
-        /*
-         * If there's no pid, we should be the first user.
-         */
-        if (rpciod_users > 1)
-                printk(KERN_WARNING "rpciod_up: no workqueue, %u users??\n", rpciod_users);
+
+        /* Guard against races with rpciod_down() */
+        if (rpciod_workqueue != NULL)
+                goto out_ok;
         /*
          * Create the rpciod thread and wait for it to start.
          */
+        dprintk("RPC:       creating workqueue rpciod\n");
         error = -ENOMEM;
         wq = create_workqueue("rpciod");
-        if (wq == NULL) {
-                printk(KERN_WARNING "rpciod_up: create workqueue failed, error=%d\n", error);
-                rpciod_users--;
+        if (wq == NULL)
                 goto out;
-        }
+
         rpciod_workqueue = wq;
         error = 0;
+out_ok:
+        atomic_inc(&rpciod_users);
 out:
         mutex_unlock(&rpciod_mutex);
         return error;
@@ -1077,23 +1076,17 @@ out:
 void
 rpciod_down(void)
 {
+        if (!atomic_dec_and_test(&rpciod_users))
+                return;
+
         mutex_lock(&rpciod_mutex);
-        dprintk("RPC:       rpciod_down sema %u\n", rpciod_users);
-        if (rpciod_users) {
-                if (--rpciod_users)
-                        goto out;
-        } else
-                printk(KERN_WARNING "rpciod_down: no users??\n");
+        dprintk("RPC:       destroying workqueue rpciod\n");
 
-        if (!rpciod_workqueue) {
-                dprintk("RPC:       rpciod_down: Nothing to do!\n");
-                goto out;
+        if (atomic_read(&rpciod_users) == 0 && rpciod_workqueue != NULL) {
+                rpciod_killall();
+                destroy_workqueue(rpciod_workqueue);
+                rpciod_workqueue = NULL;
         }
-        rpciod_killall();
-
-        destroy_workqueue(rpciod_workqueue);
-        rpciod_workqueue = NULL;
- out:
         mutex_unlock(&rpciod_mutex);
 }