On Wed, 2018-08-22 at 09:02 +0200, Christoph Hellwig wrote: > On Thu, Aug 09, 2018 at 10:27:46AM +1000, Benjamin Herrenschmidt wrote: > > On Mon, 2018-07-30 at 18:38 +0200, Christoph Hellwig wrote: > > > The requirement to disable local irqs over kmap_atomic is long gone, > > > so remove those calls. > > > > Really ? I'm trying to verify that and getting lost in a mess of macros > > from hell in the per-cpu stuff but if you look at our implementation > > of kmap_atomic_prot(), all it does is a preempt_disable(), and then > > it uses kmap_atomic_idx_push(): > > > > int idx = __this_cpu_inc_return(__kmap_atomic_idx) - 1; > > > > Note the use of __this_cpu_inc_return(), not this_cpu_inc_return(), > > ie this is the non-interrupt safe version... > > Looks like the powerpc variant indeed isn't save. > > I did look a bit more through the code and history, and it seems > like we remove the need to disable irqs when called from process > context a while ago, but we still require disabling irqs when called > from irq context. Given that this code can also be called from > irq context we'll have to keep the local_irq_save. This is the same with x86 no ? 32-bit x86 kmap_atomic_prot is the same as ours... In fact I wonder why the preempt_disable() in there since it needs to be protected against interrupt ? Or is it that we never actually call kmap_atomic_* these days from interrupt, and the atomic versions are just about dealing with spinlocks ? Cheers, Ben.
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