Re: [PATCH -next v1 05/12] srcu: Don't queue workqueue handlers to never-online CPUs

[Boqun Feng <boqun@kernel.org>]

On Mon, May 18, 2026 at 07:05:36PM +0200, Uladzislau Rezki wrote:
> On Mon, May 18, 2026 at 09:13:46AM -0700, Boqun Feng wrote:
> > On Sun, May 17, 2026 at 09:11:10PM +0200, Thorsten Leemhuis wrote:
> > > On 5/17/26 20:03, Paul E. McKenney wrote:
> > > > On Sun, May 17, 2026 at 02:47:55PM +0200, Uladzislau Rezki wrote:
> > > >> On Wed, May 13, 2026 at 12:38:01PM +0200, Thorsten Leemhuis wrote:
> > > >>> On 5/11/26 19:54, Uladzislau Rezki (Sony) wrote:
> > > >>>> From: "Paul E. McKenney" <paulmck@kernel.org>
> > > >>>>
> > > >>>> While an srcu_struct structure is in the midst of switching from CPU-0
> > > >>>> to all-CPUs state, it can attempt to invoke callbacks for CPUs that
> > > >>>> have never been online.  Worse yet, it can attempt in invoke callbacks
> > > >>>> for CPUs that never will be online, even including imaginary CPUs not in
> > > >>>> cpu_possible_mask.  This can cause hangs on s390,
> > > >>>
> > > >>> Uladzislau, Paul, according to the fixes tag below this change fixes a
> > > >>> change that went into 7.0-rc6 -- and apparently causes a "hang" on some
> > > >>> architectures. So shouldn't this be heading to mainline instead of
> > > >>> -next? Ideally with a stable tag to ensure backporting to 7.0.y, but
> > > >>> that is a separate decision?
> > > >>>
> > 
> > FWIW, I'm happy to create an urgent PR to Linus with this fix. Since it
> > fixes a commit in the previous urgent fix PR from me. Ulad, let me know
> > if you want me to do it.
> > 
> I do not mind :) So i can drop this patch!
> 

Alright, I created the fix branch at:

	https://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux.git/log/?h=fixes.v7.1

And I'm going to throw some tests on it. Will send the pull request
tomorrow.

Regards,
Boqun

> --
> Uladzislau Rezki