Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

Andy Lutomirski
2016-06-24T17:47:25Z

On Fri, Jun 24, 2016 at 10:40 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Fri, Jun 24, 2016 at 10:21 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> But as mentioned, I must have missed something. There were a number of
>> places where the code used the task_stack_page() and
>> task_thread_info() interchangably, which used to work and is no longer
>> true. There might simply be cases I missed.
>
> .. and immediately as I wrote that, I went "Duh".
>
> One place I missed was free_thread_info(), which should now free the
> stack, not the ti pointer. But it does
>
> struct page *page = virt_to_page(ti);
>
> and frees that, which is bogus. It turns out that we do do
>
> free_thread_info(tsk->stack);
>
> which is bogus too, and undoes it, but I think I have a few new places
> to look at..

Try patching in this thing, which cleans up a bunch of that core crap:

https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/vmap_stack&id=7ca9fb6bbf2838cc94b2af41e94854d02649c58c

It might not apply without the rest of my series, though.

FWIW, your patch is much more lenient than my approach: I was planning
prohibiting architectures from supplying their own struct thread_info
if they put it in task_struct. To make that work, I have patches to
remove everything but cpu, flags, and task from x86's thread_info
first. I'm planning on tidying them up and sending them out after the
vmap stack stuff lands in -tip -- I don't want to have big series that
depend on each other flying around by email at the same time, because
everyone will go nuts trying to figure out what applies where.

--Andy