Re: preempt bug in set_pmd_pfn?

[Ingo Molnar <mingo@elte.hu>]

* Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> It seems to me that the correct fix is to just make __set_fixmap 
> disable preemption for its duration; it probably doesn't make much 
> difference for the native case, and it makes Xen happy.

actually, i think the correct approach is to remove the TLB flushing and 
perhaps to check that the old pte is not present. Do we ever _change_ 
mappings via __set_fixmap()? I think we only ever install them.

but if we ever change them somewhere then the correct approach is to do 
a flush_tlb_all(). It's not just about preemption but about the fact 
that we modified the kernel address space and we must propagate that to 
all CPUs.

the vmalloc() backtrace you sent - how did set_pte_pfn() get into that 
codepath - vmalloc shouldnt be using __set_fixmap().

	Ingo