Re: RT-friendly IRQ management in USB

On 7/3/07, Jiri Kosina <[email protected]> wrote:
> On Mon, 2 Jul 2007, Alan Cox wrote:
>
> > >     spin_lock_irqsave(&some_lock, flags);
> > >     ...
> > >     spin_unlock(&some_lock);
> > >     usb_hcd_giveback_urb(hcd, urb);
> > >     local_irq_restore(flags);
> > > or is there a better approach?
> > Why not just bite the bullet and change the callback convention. The
> > lock verification code should catch the cases that matter and which are
> > overlooked on a code scan. You could also change the name of the
> > callback to be sure it breaks anything out of tree that isn't fixed.
>
> Plus the code above code will break as soon as someone removes the
> preempt_disable() from spin_lock_irqsave() and preempt_enable() from
> spin_lock_irqrestore() -- which would in fact be a good optimization to do
> (local interrupts are disabled, so there is no need to disable
> preemption).
>
> But this has to wait until all the places in kernel which do this kind of
> incorrect pairing are fixed. I'd ceratinly vote for not adding any more of
> them.
>
>         spin_lock_irqsave(&some_lock, flags);
>         ...
>         preempt_disable();
>         spin_unlock(&some_lock);
>         usb_hcd_giveback_urb(hcd, urb);
>         local_irq_restore(flags);
>         preempt_enable();
>
> Would make it working in both cases. Not a nice thing, indeed :)

So looks like we don't have (yet) a way to make it work nicely in both
cases... does anyone has a clue about how to implement this one??

>
> --
> Jiri Kosina
>
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-- 
Best Regards,

Felipe Balbi
[email protected]

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