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.
