On Friday 26 October 2007 13:35, Benjamin Herrenschmidt wrote:
[acks]
Thanks for those...
> > Index: linux-2.6/include/asm-powerpc/mmu_context.h
> > ===================================================================
> > --- linux-2.6.orig/include/asm-powerpc/mmu_context.h
> > +++ linux-2.6/include/asm-powerpc/mmu_context.h
> > @@ -129,7 +129,7 @@ static inline void get_mmu_context(struc
> > steal_context();
> > #endif
> > ctx = next_mmu_context;
> > - while (test_and_set_bit(ctx, context_map)) {
> > + while (test_and_set_bit_lock(ctx, context_map)) {
> > ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1,
> > ctx); if (ctx > LAST_CONTEXT)
> > ctx = 0;
> > @@ -158,7 +158,7 @@ static inline void destroy_context(struc
> > {
> > preempt_disable();
> > if (mm->context.id != NO_CONTEXT) {
> > - clear_bit(mm->context.id, context_map);
> > + clear_bit_unlock(mm->context.id, context_map);
> > mm->context.id = NO_CONTEXT;
> > #ifdef FEW_CONTEXTS
> > atomic_inc(&nr_free_contexts);
>
> I don't think the previous code was wrong... it's not a locked section
> and we don't care about ordering previous stores. It's an allocation, it
> should be fine. In general, bitmap allocators should be allright.
Well if it is just allocating an arbitrary _number_ out of a bitmap
and nothing else (eg. like the pid allocator), then you don't need
barriers.
> Ignore the FEW_CONTEXTS stuff for now :-) At this point, it's UP only
> and will be replaced sooner or later.
OK. Then I agree, provided you're doing the correct synchronisation
or flushing etc. when destroying a context (which presumably you are).
I'll drop those bits then.
Thanks,
Nick
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