On Mon, 2009-08-03 at 11:21 -0500, Kumar Gala wrote: > On Aug 2, 2009, at 9:03 PM, Michael Ellerman wrote: > > > On Sat, 2009-08-01 at 08:29 +1000, Benjamin Herrenschmidt wrote: > >> On Thu, 2009-07-30 at 22:35 -0500, Kumar Gala wrote: > >>>> /* XXX This clear should ultimately be part of > >>> local_flush_tlb_mm */ > >>>> - __clear_bit(id, stale_map[cpu]); > >>>> + for (cpu = cpu_first_thread_in_core(cpu); > >>>> + cpu <= cpu_last_thread_in_core(cpu); cpu++) > >>>> + __clear_bit(id, stale_map[cpu]); > >>>> } > >>> > >>> This looks a bit dodgy. using 'cpu' as both the loop variable and > >>> what you are computing to determine loop start/end.. > >>> > >> Hrm... I would have thought that it was still correct... do you see > >> any > >> reason why the above code is wrong ? because if not we may be > >> hitting a > >> gcc issue... > >> > >> IE. At loop init, cpu gets clamped down to the first thread in the > >> core, > >> which should be fine. Then, we compare CPU to the last thread in core > >> for the current CPU which should always return the same value. > >> > >> So I'm very interested to know what is actually wrong, ie, either I'm > >> just missing something obvious, or you are just pushing a bug under > >> the > >> carpet which could come back and bit us later :-) > > > > for (cpu = cpu_first_thread_in_core(cpu); > > cpu <= cpu_last_thread_in_core(cpu); cpu++) > > __clear_bit(id, stale_map[cpu]); > > > > == > > > > cpu = cpu_first_thread_in_core(cpu); > > while (cpu <= cpu_last_thread_in_core(cpu)) { > > __clear_bit(id, stale_map[cpu]); > > cpu++; > > }
cpu_last_thread_in_core(cpu) is a moving target. You want something like: cpu = cpu_first_thread_in_core(cpu); last = cpu_last_thread_in_core(cpu); while (cpu <= last) { __clear_bit(id, stale_map[cpu]); cpu++; } > > > > cpu = 0 > > cpu <= 1 > > cpu++ (1) > > cpu <= 1 > > cpu++ (2) > > cpu <= 3 > > ... > > Which is pretty much what I see, in a dual core setup, I get an oops > because we are trying to clear cpu #2 (which clearly doesn't exist) > > cpu = 1 > (in loop) > clearing 1 > clearing 2 > OOPS > > - k -- David Kleikamp IBM Linux Technology Center _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev