Am Freitag, 30. März 2007 22:59 schrieb David Brownell:
> On Friday 30 March 2007 1:38 pm, Oliver Neukum wrote:
> > Am Freitag, 30. März 2007 22:04 schrieb David Brownell:
> > > Remember that if every completion callback does
> > >
> > > status = urb->status;
> > >
> > > at the top, the urb->status issue will by definition go away. That's
> >
> > Only if it does smp_mb(), which is the whole point of this thread.
>
> Nope. If an smp_mb() is needed, the reason is because of other
> driver-internal bugs.
>
> Remember that the driver isn't allowed to so much as *LOOK* at any
> field of an URB until the completion callback. That generalizes:
> it mustn't do so until that callback (cleanly) hands the URB back
Yes and the callback is guaranteed that all the urb's fields are
valid. Which is the whole point. Is that guarantee only valid to the
callback or to the whole driver?
CPU A (callback) CPU B
flag = 1; if (!flag) barrier();
a = urb->status; b = urb->status;
Do we guarantee a==b or don't we?
Regards
Oliver
PS: Alan to CC because he looked at that stuff in detail
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