Re: [PATCH] drm/sched: Remove optimization that causes hang when killing dependent jobs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Jul 16, 2025 at 12:58:28PM +0200, Christian König wrote:
> On 16.07.25 12:46, Philipp Stanner wrote:
> > +Cc Greg, Sasha
> > 
> > On Wed, 2025-07-16 at 12:40 +0200, Michel Dänzer wrote:
> >> On 16.07.25 11:57, Philipp Stanner wrote:
> >>> On Wed, 2025-07-16 at 09:43 +0000, cao, lin wrote:
> >>>>
> >>>> Hi Philipp,
> >>>>
> >>>>
> >>>> Thank you for the review. I found that this optimization was
> >>>> introduced 9 years ago in commit
> >>>> 777dbd458c89d4ca74a659f85ffb5bc817f29a35 ("drm/amdgpu: drop a
> >>>> dummy
> >>>> wakeup scheduler").
> >>>>
> >>>>
> >>>> Given that the codebase has undergone significant changes over
> >>>> these
> >>>> 9 years. May I ask if I still need to include the Fixes: tag?
> >>>
> >>> Yes. It's a helpful marker to see where the problem comes from, and
> >>> it
> >>> adds redundancy helping the stable-kernel maintainers in figuring
> >>> out
> >>> to which kernels to backport it to.
> >>>
> >>> If stable can't apply a patch to a very old stable kernel because
> >>> the
> >>> code base changed too much, they'll ping us and we might provide a
> >>> dedicated fix.
> >>>
> >>> So like that:
> >>>
> >>> Cc: stable@vger.kernel.org # v4.6+
> >>> Fixes: 777dbd458c89 ("drm/amdgpu: drop a dummy wakeup scheduler")
> >>
> >> FWIW, Fixes: alone is enough for getting backported to stable
> >> branches, Cc: stable is redundant with it.
> > 
> > Both are used all the time together, though. And the official
> > documentation does not list dropping Cc: stable as a valid option in
> > this regard
> > 
> > https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-1
> > 
> > 
> > As long as the official documentation demands it, I'm not willing to
> > drop it. If the docu were to be changed, that would be fine by me, too.
> 
> As far as I understand "CC: stable" and "Fixes:" tags are to handle two distinct use cases.

Yes.

> "CC: stable..." means please backport, eventually with a kernel version and/or necessary pre-requisites.

Yes.

> "Fixes:" only backport if you have this patch in your tree as well. In other words it is a restriction when to backport something.

No.

"Fixes:" is only for you to say "this commit fixes this other commit".
And when you add a cc: stable, that will get you a FAILED email if the
commit does NOT apply that far back.

"Fixes:" on its own does NOT mean it will ever be backported to the
stable trees.  But because so many people KEEP GETTING THIS WRONG
(despite cc: stable@ happening first in history _before_ Fixes: came
about), we do try to sweep the tree every so often and do a "best
effort" backport of those only marked with Fixes:

But that happens later, if at all, and you do NOT get a FAILED email if
a patch does not apply to a stable branch.

So ALWAYS use cc: stable@ for something you want backported to stable
kernels.  That's what the documentation states, and is what we have been
doing for 15+ years now (is it 20?).

thanks,

greg k-h