Am Samstag, 31. März 2007 04:59 schrieb Alan Stern:
> isn't clean -- but several drivers do it this way. I'm not even certain
> that adding smp_mb() to the completion routine will really fix it; memory
> barriers have to be used in pairs, and so there would also need to be a
> barrier between the test of private_data->urb_done and the call to
> use(urb).
>
In the example you have given smp_rmb() would be required.
However we have:
CPU A CPU B
a = urb->status if (flag)
flag = 1 urb->status = x
abstractly speaking. CPU A needs a memory barrier.
Are you saying that CPUs may do speculative _writes_ ?
Regards
Oliver
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