Re: 2.6.17-rc5-mm1

Steven Rostedt
2006-05-31T11:51:07Z

On Wed, 2006-05-31 at 08:31 +0200, Ingo Molnar wrote:
> * Andrew Morton <akpm@osdl.org> wrote:
>
> > Without having looked at it very hard, I'd venture that this is a
> > false positive - that driver uses disable_irq() to prevent reentry
> > onto that lock.
>
> correct.
>
> > It does that because it knows it's about to spend a long time talking
> > with the mii registers and it doesn't want to do that with interrupts
> > disabled.
>
> i still consider it a 'quirky' locking construct, because disabling
> interrupts for a long time also disables all other devices sharing the
> same IRQ line - not nice.
>
> Also, this is a really hard case for lockdep to detect automatically.
> (fortunately it's also relatively rare)

What's the standard way to teach lockdep about this?

>
> OTOH, the straightforward lockdep workaround would be to take the
> spinlock and thus disable all local interrupts - not too nice either.
>
> Albeit in some ways it's still a bit nicer conceptually than disabling
> the irq line, because other CPUs are still operational, and under
> certain locking designs [preempt-rt] spin_lock_irq() does not disable
> local interrupts.
>
> Steve, can you think of any better solution? I dont have this card.

Until this popped up, I didn't know I had this card either ;)
(the last time we dealt with this card was to help someone else)

Anyway, I'll look into the way this card works and start to play with it
when I get some time.

Andrew, do you have any docs that I can read to understand the card a
little better?

Thanks,

-- Steve