> From: johan verrept <[EMAIL PROTECTED]>
> To: linux-usb-devel <[EMAIL PROTECTED]>
> CC: Johannes Erdfelt <[EMAIL PROTECTED]>
> Date: Mon, 16 Apr 2001 18:27:46 +0200
> When a hub interrupt urb completes hub_irq() checks whether
> the waitqueue is active (if the hub thread is sleeping). If it
> isn't sleeping, the hub never gets scheduled for event processing.
> It causes a problem with the uml hcd. [...]
I also disagree with this. Almost ALL instances of the following
code in kernel are racy:
if (waitqueue_active(&wq))
wake_up(&wq);
The right approach is to call wake_up regardless, as a rule of thumb.
> The only reason I see for this is that the list spinlock is held
> during the entire usb_hub_events()
> call and that would cause hub_irq() to block.
The statement above is not true. This is the 2.4.3 code that I have:
static void usb_hub_events(void)
{
.....................
while (1) {
spin_lock_irqsave(&hub_event_lock, flags);
if (list_empty(&hub_event_list))
break;
tmp = hub_event_list.next;
hub = list_entry(tmp, struct usb_hub, event_list);
list_del(tmp);
INIT_LIST_HEAD(tmp);
down(&khubd_sem); // <=== replaced in my last patch
spin_unlock_irqrestore(&hub_event_lock, flags);
....................
}
}
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