On Wed, Jan 28, 2015 at 04:46:37PM +0100, Peter Zijlstra wrote: > On Wed, Jan 28, 2015 at 01:24:12AM +0100, Frederic Weisbecker wrote: > > PREEMPT_ACTIVE implies non-preemptible context and thus atomic context > > despite what in_atomic*() APIs reports about it. These functions > > shouldn't ignore this value like they are currently doing. > > > > It appears that these APIs were ignoring PREEMPT_ACTIVE in order to > > ease the check in schedule_debug(). Meanwhile it is sufficient to rely > > on PREEMPT_ACTIVE in order to disable preemption in __schedule(). > > > > So lets fix the in_atomic*() APIs and simplify the preempt count ops > > on __schedule() callers. > > So what I think the history is here is that PREEMPT_ACTIVE is/was seen > as a flag, protecting recursion, not so much a preempt-disable. > > By doing this, you loose that separation.
Indeed, preemption disablement is a side effet. > > Note that (at least on x86) we have another flag in the preempt count. > > And I don't think the generated code really changes, the only difference > is the value added/subtracted and that's an encoded immediate I think. Right the resulting code isn't optimized at all with this patch. Only the C code was deemed to be more simple but actually it isn't since we are abusing a side effect property. I'm dropping this patch then. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
