[PATCH] SUNRPC: Fix potential deadlock in RPC code

In rpc_wake_up() and rpc_wake_up_status(), it is possible for the call to
__rpc_wake_up_task() to fail if another thread happens to be calling
rpc_wake_up_task() on the same rpc_task.

Problem noticed by Bruno Faccini.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

net/sunrpc/sched.c

@@ -515,16 +515,14 @@ struct rpc_task * rpc_wake_up_next(struct rpc_wait_queue *queue)
  */
 void rpc_wake_up(struct rpc_wait_queue *queue)
 {
-	struct rpc_task *task;
-
+	struct rpc_task *task, *next;
 	struct list_head *head;
+
 	spin_lock_bh(&queue->lock);
 	head = &queue->tasks[queue->maxpriority];
 	for (;;) {
-		while (!list_empty(head)) {
-			task = list_entry(head->next, struct rpc_task, u.tk_wait.list);
+		list_for_each_entry_safe(task, next, head, u.tk_wait.list)
 			__rpc_wake_up_task(task);
-		}
 		if (head == &queue->tasks[0])
 			break;
 		head--;
@@ -541,14 +539,13 @@ void rpc_wake_up(struct rpc_wait_queue *queue)
  */
 void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
 {
+	struct rpc_task *task, *next;
 	struct list_head *head;
-	struct rpc_task *task;
 
 	spin_lock_bh(&queue->lock);
 	head = &queue->tasks[queue->maxpriority];
 	for (;;) {
-		while (!list_empty(head)) {
-			task = list_entry(head->next, struct rpc_task, u.tk_wait.list);
+		list_for_each_entry_safe(task, next, head, u.tk_wait.list) {
 			task->tk_status = status;
 			__rpc_wake_up_task(task);
 		}