mmotm threatens ppc preemption again

[Jeremy Fitzhardinge]

On 03/30/2011 05:52 PM, Benjamin Herrenschmidt wrote:
> We deal with preemption already since the PTL turns into a mutex on -rt,
> so we could bring that patch into mainline. The easiest approach however
> for now would be to not do the kernel batched updates on kernel
> (solution 4), and I can sort it out later if I want to enable it.
>
> The problem is that it's hard for me to "fix" that with the current
> accessors as arch_enter_lazy_mmu_mode() don't get any argument that
> could point me to which mm is being operated on.
>
> Jeremy, I haven't had a chance to look at your patches in detail, do
> you just use those accessors or do you create new ones for batching
> kernel updates in which case powerpc could just make them do nothing ?
>
> Else, we could have one patch that adds an mm argument accross the tree,
> it shouldn't be too hard.

No, its the same accessors for both, since the need to distinguish them
hasn't really come up.  Could you put a "if (preemptable()) return;"
guard in your implementations?

Otherwise I have no objections to passing the mm in (we'll probably just
continue to ignore the arg in x86-land).

Thanks,
    J