Re: [PATCH RFC 1/3] arm64/gcs: Support reuse of GCS for exited threads

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Sep 25, 2025 at 08:00:40PM +0100, Mark Brown wrote:
> On Thu, Sep 25, 2025 at 07:36:50PM +0100, Catalin Marinas wrote:
> > On Thu, Sep 25, 2025 at 06:01:07PM +0100, Mark Brown wrote:
> > > On Thu, Sep 25, 2025 at 05:46:46PM +0100, Catalin Marinas wrote:
> > > > On Sun, Sep 21, 2025 at 02:21:35PM +0100, Mark Brown wrote:
> 
> > > We can't have scheduled?  That's actually a pleasant surprise, that was
> > > the main hole I was thinking of in the cover letter.
> 
> > Well, double-check. AFAICT, gcs_free() is only called on the exit_mm()
> > path when a thread dies.
> 
> > I think gcs_free() may have been called in other contexts before the
> > cleanups you had in 6.16 (there were two more call sites for
> > gcs_free()). If that's the case, we could turn these checks into
> > WARN_ON_ONCE().
> 
> Yeah, just I need to convince myself that we're always running the
> exit_mm() path in the context of the exiting thread.  Like you say it
> needs checking but hopefully you're right and the current code is more
> correct than I had thought.

The only path to gcs_free() is via mm_release() -> deactivate_mm().
mm_release() is called from either exit_mm_release() or
exec_mm_release(). These two functions are only called with current and
current->mm.

I guess for historical reasons, they take task and mm parameters but in
recent mainline, they don't seem to get anything other than current.

-- 
Catalin