lkml.org 
[lkml]   [2007]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] synchronize_irq needs a barrier
From
Date

> 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.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-19 06:39    [W:0.178 / U:0.196 seconds]
©2003-2014 Jasper Spaans. Advertise on this site