Re: Deadlock in net/sunrpc/sched.c

[Simon Derr]

On Thu, 2 Mar 2006, Simon Derr wrote:

> Index: linux-2.6.12.6/net/sunrpc/sched.c
> ===================================================================
> --- linux-2.6.12.6.orig/net/sunrpc/sched.c	2005-08-29 18:55:27.000000000 +0200
> +++ linux-2.6.12.6/net/sunrpc/sched.c	2006-03-02 12:41:42.000000000 +0100
> @@ -400,16 +400,16 @@ __rpc_default_timer(struct rpc_task *tas
>   */
>  void rpc_wake_up_task(struct rpc_task *task)
>  {
> +	struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
> +	spin_lock_bh(&queue->lock);
>  	if (rpc_start_wakeup(task)) {
>  		if (RPC_IS_QUEUED(task)) {
> -			struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
>  
> -			spin_lock_bh(&queue->lock);
>  			__rpc_do_wake_up_task(task);
> -			spin_unlock_bh(&queue->lock);
>  		}
>  		rpc_finish_wakeup(task);
>  	}
> +	spin_unlock_bh(&queue->lock);
>  }

Hmm, this is just to show how to reverse the locking order.
I'm not too familiar with the rpc_tasks, and 
task->u.tk_wait.rpc_waitq might not be valid.

Maybe this would be better:



--- linux-2.6.12.6.orig/net/sunrpc/sched.c	2006-03-02 13:11:51.000000000 +0100
+++ linux-2.6.12.6/net/sunrpc/sched.c	2006-03-02 13:16:19.000000000 +0100
@@ -400,15 +400,14 @@ __rpc_default_timer(struct rpc_task *tas
  */
 void rpc_wake_up_task(struct rpc_task *task)
 {
-	if (rpc_start_wakeup(task)) {
-		if (RPC_IS_QUEUED(task)) {
-			struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
-
-			spin_lock_bh(&queue->lock);
+	if (RPC_IS_QUEUED(task)) {
+		struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
+		spin_lock_bh(&queue->lock);
+		if (rpc_start_wakeup(task))  {
 			__rpc_do_wake_up_task(task);
-			spin_unlock_bh(&queue->lock);
+			rpc_finish_wakeup(task);
 		}
-		rpc_finish_wakeup(task);
+		spin_unlock_bh(&queue->lock);
 	}
 }
 
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