Re: frequent lockups in 3.18rc4

[Andy Lutomirski]

On Tue, Dec 16, 2014 at 4:00 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Dec 16, 2014 at 3:02 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>
>> OK, should we just stick it in the x86 tree and see if anything
>> explodes? ;-)
>
> Gaah, I got confused about the patches.
>
> And something did explode, it showed some Xen nasties. Xen has that
> odd "we don't share PMD entries between MM's" thing going on, which
> means that the vmalloc fault thing does actually have to occasionally
> walk two levels rather than just copy the top level. I'm still not
> sure why Xen doesn't share PMD's, since threads that shame the MM
> clearly can share PMD's within Xen, but I gave up on it.

Sounds like it's time to ask Konrad, the source of all Xen understanding :)

Linus, do you have a pointer to whatever version of the patch you tried?

--Andy

>
> That said, making x86-64 use "read_cr3()" instead of
> "current->active_mm" would at least make things a bit safer wrt NMI's
> during the task switch, of course.  So *some* 32/64-bit consolidation
> should be done, but my patch went a bit too far for Xen.
>
>                       Linus



-- 
Andy Lutomirski
AMA Capital Management, LLC
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