On Sat, 17 Dec 2005, Nicolas Pitre wrote:
>
> Now if you don't disable interrupts then nothing prevents an interrupt
> handler, or another thread if kernel preemption is allowed
Preemption, yes. Interrupts no.
> to come
> along right between (2) and (4) to call up() or down() which will
> make the sem count inconsistent as soon as the interrupted down() or
> up() is resumed.
An interrupt can never change the value without changing it back, except
for the old-fashioned use of "up()" as a completion (which I don't think
we do any more - we used to do it for IO completion a looong time ago).
So I think the interrupt disable could be removed for UP, at least for
non-preemption.
(Of course, maybe it's not worth it. It might not be a big performance
issue).
Linus
