> >additionally: if the data structure is never accessed from IRQ handlers
> >then it's fast and safe to use a semaphore instead of a spinlock.
>
> You can access it also from irq handlers but you are allowed to use only
> down_trylock(). (a similar things happens in show_buffers() in buffer.c
> but with spinlocks)
yep you are right. This technique can be used for event-driven state
machines, but cannot be used if the IRQ _must_ get access to that data
structure. Ie. show_buffers() is fine, because the worst that can happen
is that we do not see a debugging message.
-- mingo
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