> What may happen is that action can either float upwards to give
>
> spin_lock
> action
> set IRQ_INPROGRESS
> spin_unlock
>
> spin_lock
> clear IRQ_INPROGRESS
> spin_unlock
>
> or it can float downwards to give
>
> spin_lock
> set IRQ_INPROGRESS
> spin_unlock
>
> spin_lock
> clear IRQ_INPROGRESS
> action
> spin_unlock
>
Well, we are generally safer here. That is, unless action is a store,
it will not pass spin_lock, at least not on powerpc afaik.
In fact, if action, as it is in our case, is something like
if (foo)
return;
We cant execute the store inside spin_lock() without having loaded
foo, there is an implicit dependency here.
But anyway, Linus patch fixes that too if it was a problem. Now if
we grep for while (test_bit and while (!test_bit I'm sure we'll find
other similar surprises.
That's also one of the reasons why I _love_ nick patches that add a
proper lock/unlock API on bits, because at least those who are doing
those hand-made pseudo-locks with bitops to save space will be
getting a proper lock/unlock API, no more excuse.
The network stack is doing more fancy things so it's harder (though I
wonder sometimes if it's really worth the risks taken for not using
spinlocks... maybe).
Ben.
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