Re: RT and Cascade interrupts

[Oleg Nesterov <oleg@tv-sign.ru>]

__rpc_execute() calls ->tk_exit and goes to 'restarted' label.
What if ->tk_exit calls rpc_sleep_on() ? If it is possible, we
have a race.

CPU_0 (main loop in rpc_execute restarted)		CPU_1

rpc_delete_timer:
	if (RPC_IS_QUEUED())	// YES
		return;
							rpc_run_timer:
								rpc_wake_up_task:
									clear_bit(RPC_TASK_QUEUED)
								preemption, or long interrupt

if (!RPC_IS_QUEUED())		// YES
	task->tk_action()
		__rpc_add_timer:
			set_bit(RPC_TASK_HAS_TIMER)
			mod_timer();
								clear_bit(RPC_TASK_HAS_TIMER)

Now we have pending timer without RPC_TASK_HAS_TIMER bit set.

Is this patch makes any sense?

Oleg.

--- 2.6.12-rc5/net/sunrpc/sched.c~	Sun May 29 15:09:25 2005
+++ 2.6.12-rc5/net/sunrpc/sched.c	Sun May 29 15:11:24 2005
@@ -135,8 +135,6 @@ __rpc_add_timer(struct rpc_task *task, r
 static void
 rpc_delete_timer(struct rpc_task *task)
 {
-	if (RPC_IS_QUEUED(task))
-		return;
 	if (test_and_clear_bit(RPC_TASK_HAS_TIMER, &task->tk_runstate)) {
 		del_singleshot_timer_sync(&task->tk_timer);
 		dprintk("RPC: %4d deleting timer\n", task->tk_pid);
@@ -566,7 +564,6 @@ static int __rpc_execute(struct rpc_task
 
 	BUG_ON(RPC_IS_QUEUED(task));
 
- restarted:
 	while (1) {
 		/*
 		 * Garbage collection of pending timers...
@@ -607,6 +604,7 @@ static int __rpc_execute(struct rpc_task
 			unlock_kernel();
 		}
 
+ restarted:
 		/*
 		 * Lockless check for whether task is sleeping or not.
 		 */