Re: [PATCH v2 37/59] x86/putuser: Provide room for padding

[Peter Zijlstra]

On Mon, Sep 05, 2022 at 09:16:43AM +0200, Peter Zijlstra wrote:
> On Sat, Sep 03, 2022 at 10:26:45AM -0700, Linus Torvalds wrote:
> > On Fri, Sep 2, 2022 at 2:46 PM Linus Torvalds
> > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > Hmm. It doesn't look too horrible, but yeah, fi it still ends up
> > > getting the same padding overhead I'm not sure it ends up really
> > > mattering.
> > 
> > Oh, and I think it's buggy anyway.
> > 
> > If there are any tail-calls to a leaf function, the tracking now gets
> > out of whack. So it's no longer a "don't bother counting the last
> > level", now it ends up being a "count got off by one".
> 
> See validate_sibling_call(), it too calls validate_call().
> 
> (Although prehaps I should go s/sibling/tail/ on all that for clarity)

Ah, no, you're right and I needed more wake-up juice.