> > * David Hildenbrand <d...@linux.vnet.ibm.com> wrote: > > > > On Thu, May 07, 2015 at 12:50:53PM +0200, David Hildenbrand wrote: > > > > Just to make sure we have a common understanding (as written in my cover > > > > letter): > > > > > > > > Your suggestion won't work with !CONFIG_PREEMPT > > > > (!CONFIG_PREEMPT_COUNT). If > > > > there is no preempt counter, in_atomic() won't work. > > > > > > But there is, we _always_ have a preempt_count, and irq_enter() et al. > > > _always_ increment the relevant bits. > > > > > > The thread_info::preempt_count field it never under PREEMPT_COUNT > > > include/asm-generic/preempt.h provides stuff regardless of > > > PREEMPT_COUNT. > > > > > > See how __irq_enter() -> preempt_count_add(HARDIRQ_OFFSET) -> > > > __preempt_count_add() _always_ just works. > > > > > > Its only things like preempt_disable() / preempt_enable() that get > > > munged depending on PREEMPT_COUNT/PREEMPT. > > > > > > > Sorry for the confusion. Sure, there is always the count. > > > > My point is that preempt_disable() won't result in an in_atomic() == true > > with !PREEMPT_COUNT, so I don't see any point in adding in to the pagefault > > handlers. It is not reliable. > > That's why we have the preempt_count_inc()/dec() methods that are > always available. > > So where's the problem?
My point: Getting rid of PREEMPT_COUNT (and therefore always doing preempt_count_inc()/dec()) will make preempt_disable() __never__ be a NOP. So with !CONFIG_PREEMPT we will do preemption stuff that is simply not needed. Two concepts that share one mechanism. I think this is broken. David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
