FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for disabled tasks" failed to apply to 7.1-stable tree

FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for disabled tasks" failed to apply to 7.1-stable tree

[gregkh]

The patch below does not apply to the 7.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-7.1.y
git checkout FETCH_HEAD
git cherry-pick -x 0e2f4ab68a89fad42e0f5a9ff4b740738e7aa1d6
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026072131-citation-reshape-587c@gregkh' --subject-prefix 'PATCH 7.1.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0e2f4ab68a89fad42e0f5a9ff4b740738e7aa1d6 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>

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index aeee44e016ab..e3fa7b2fac9d 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -3967,6 +3967,17 @@ static void reweight_task_scx(struct rq *rq, struct task_struct *p,
 	if (task_dead_and_done(p))
 		return;
 
+	/*
+	 * When switching sched_class away from SCX, reweight_task_scx()
+	 * is called _after_ scx_disable_task(). Skip calling ops.set_weight()
+	 * since the BPF scheduler may have already forgotten the task in
+	 * ops.disable().
+	 * p->scx.weight will be recalculated in scx_enable_task() if the task
+	 * ever returns to SCX class.
+	 */
+	if (scx_get_task_state(p) != SCX_TASK_ENABLED)
+		return;
+
 	p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight));
 	if (SCX_HAS_OP(sch, set_weight))
 		SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight);

Re: FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for disabled tasks" failed to apply to 7.1-stable tree

[Kuba Piecuch]

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 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 5d2d19473a82..8429bebc21a1 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3904,6 +3904,17 @@ static void reweight_task_scx(struct rq *rq, struct task_struct *p,
        if (task_dead_and_done(p))
                return;
 
+       /*
+        * When switching sched_class away from SCX, reweight_task_scx()
+        * is called _after_ scx_disable_task(). Skip calling ops.set_weight()
+        * since the BPF scheduler may have already forgotten the task in
+        * ops.disable().
+        * p->scx.weight will be recalculated in scx_enable_task() if the task
+        * ever returns to SCX class.
+        */
+       if (scx_get_task_state(p) != SCX_TASK_ENABLED)
+               return;
+
        p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight));
        if (SCX_HAS_OP(sch, set_weight))
                SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight);

Re: FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for disabled tasks" failed to apply to 7.1-stable tree

[Greg KH]

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.

greg k-h

Re: FAILED: patch "[PATCH] sched_ext: Skip ops.set_weight() for disabled tasks" failed to apply to 7.1-stable tree

[Greg KH]

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

[PATCH 7.1.y] sched_ext: Skip ops.set_weight() for disabled tasks

[Kuba Piecuch]

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 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 5d2d19473a82..8429bebc21a1 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3904,6 +3904,17 @@ static void reweight_task_scx(struct rq *rq, struct task_struct *p,
 	if (task_dead_and_done(p))
 		return;
 
+	/*
+	 * When switching sched_class away from SCX, reweight_task_scx()
+	 * is called _after_ scx_disable_task(). Skip calling ops.set_weight()
+	 * since the BPF scheduler may have already forgotten the task in
+	 * ops.disable().
+	 * p->scx.weight will be recalculated in scx_enable_task() if the task
+	 * ever returns to SCX class.
+	 */
+	if (scx_get_task_state(p) != SCX_TASK_ENABLED)
+		return;
+
 	p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight));
 	if (SCX_HAS_OP(sch, set_weight))
 		SCX_CALL_OP_TASK(sch, set_weight, rq, p, p->scx.weight);
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH 7.1.y] sched_ext: Skip ops.set_weight() for disabled tasks

[Sasha Levin]

> 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().

Queued for 7.1, thanks.

-- 
Thanks,
Sasha