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Date: Tue, 21 Jul 2026 16:19:53 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Kuba Piecuch <jpiecuch@google.com>
Cc: tj@kernel.org, stable@vger.kernel.org
Subject: Re: FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for
 disabled tasks" failed to apply to 7.1-stable tree
Message-ID: <2026072139-phrasing-scroll-e4fa@gregkh>
References: <2026072131-citation-reshape-587c@gregkh>
 <DK4AN7P1B5KK.15R8G3B5L5E85@google.com>
 <2026072141-spotless-tarantula-5421@gregkh>
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In-Reply-To: <2026072141-spotless-tarantula-5421@gregkh>

On Tue, Jul 21, 2026 at 04:19:02PM +0200, Greg KH wrote:
> On Tue, Jul 21, 2026 at 01:47:04PM +0000, Kuba Piecuch wrote:
> > Hi Greg,
> > 
> > I'm unable to reproduce the failure using the steps provided.
> > The patch applies cleanly. The code compiles and tests are passing.
> > 
> > FWIW, below is the patch after cherry-picking the commit:
> > 
> > Thanks,
> > Kuba
> > 
> > ------------------------ 8< ----------------------------
> > 
> > >From adc748e669cc1564255430299abf086b9ecd9b45 Mon Sep 17 00:00:00 2001
> > From: Kuba Piecuch <jpiecuch@google.com>
> > Date: Fri, 10 Jul 2026 14:43:41 +0000
> > Subject: [PATCH] sched_ext: Skip ops.set_weight() for disabled tasks
> > 
> > When switching a task's sched_class away from sched_ext, we get the
> > following sequence of events in __sched_setscheduler():
> > 
> > sched_change_begin()
> >   switched_from_scx()
> >     scx_disable_task(p)
> >       ops.disable(p)
> > __setscheduler_params()
> >   set_load_weight()
> >     reweight_task_scx(p)
> >       ops.set_weight(p)
> > p->sched_class = next_class;
> > sched_change_end()
> >   ...
> > 
> > Notably, ops.set_weight() is called _after_ ops.disable().
> > This violates the expected semantics of the callbacks, the expectation
> > being that ops.disable() can only be followed by ops.exit_task() or
> > ops.enable().
> > 
> > Skipping the weight adjustment for disabled tasks should be harmless
> > since the weight will be recalculated in scx_enable_task() if the task
> > ever rejoins SCX.
> > 
> > Fixes: 637b0682821b ("sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern")
> > Cc: stable@vger.kernel.org # v6.19+
> > Signed-off-by: Kuba Piecuch <jpiecuch@google.com>
> > Signed-off-by: Tejun Heo <tj@kernel.org>
> > (cherry picked from commit 0e2f4ab68a89fad42e0f5a9ff4b740738e7aa1d6)
> > ---
> >  kernel/sched/ext.c | 11 +++++++++++
> 
> If you look, the original file was:
> 	kernel/sched/ext/ext.c
> your cherry-pick fixed that.
> 
> I'll take this, thanks.

Nope, the whitespace is corrupted, please send a good copy.

thanks,

greg k-h