Re: [PATCH 0/1] expand_downwards: don't require the gap if !vm_prev

From: Linus Torvalds
Date: Mon Jul 03 2017 - 12:30:59 EST

On Mon, Jul 3, 2017 at 8:49 AM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> If you think this is worth pursuing in upstream, just let me know and I
> can polish it, add a patch for the man page and other things.

Hmm. This doesn't look bad, except the bprm games there really look annoying.

Also, I'm wondering whether this should be per-thread - conceptually
"expand_stack()" really is a thread thing. All callers are using
"current", although it's not always obvious.

So I'm wondering if a slightly larger patch that simply made the
"limit" be an _argument_ to expand_stack() would clean up both of
these issues. The execve() use would simply pass in the stack limit,
and the fault users would pass in "current->expand_stack_limit".

Again, I'm not sure how many people really use multiple GROW_DOWN
stacks for threading, but it's conceptually the right thing to do, so
I think conceptually this should be per-thread. And the fact that it
might clean up the execve() thing makes me think it's the right thing
to do.

What do you think?