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SubjectRe: Fix locking in input
Hi!

> >>input uses "volatile signed char" as a shared variable between normal
> >>and interrupt threads (look at _sendbyte()). Thats bad idea, this
> >>switches it to atomic_t.
> >
> >This change looks unnecessary to me - we aren't trying to increment or
> >decrement the variable, just set it and read it. Reading and writing
> >individual bytes is atomic on any platform we care about.
> >
> >
> I think one platform (early ARM?) cannot access bytes directly, and
> implement the access with read 16-bit, change 8-bit, write back 16 bit.
> Reading/writing pointers or longs is atomic.
>
> Pavel: Do you know that atomic_set and atomic_read aren't memory barriers?
> I.e.
>
> - psmouse->ack = 0;
> + atomic_set(&psmouse->ack, 0);
> psmouse->acking = 1;
>
> It's not guaranteed that all cpus will see psmouse->ack=0 before
> psmouse->acking=1. And adding the required memory barriers usually makes
> the code completely unreadable, thus I usually give up and switch to a
> spinlock.

Would simply adding mb() there fix it? It is not performance-critical
in any way...
Pavel

--
When do you have a heart between your knees?
[Johanka's followup: and *two* hearts?]
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