Patch "sched_ext: Skip tasks with stale task_rq in bypass_lb_cpu()" has been added to the 7.0-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    sched_ext: Skip tasks with stale task_rq in bypass_lb_cpu()

to the 7.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched_ext-skip-tasks-with-stale-task_rq-in-bypass_lb_cpu.patch
and it can be found in the queue-7.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From arighi@nvidia.com Wed May 13 15:01:26 2026
From: Andrea Righi <arighi@nvidia.com>
Date: Wed, 13 May 2026 15:01:11 +0200
Subject: sched_ext: Skip tasks with stale task_rq in bypass_lb_cpu()
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Tejun Heo <tj@kernel.org>, David Vernet <void@manifault.com>, Changwoo Min <changwoo@igalia.com>
Cc: Chris Mason <clm@meta.com>, Peter Schneider <pschneider1968@googlemail.com>, sched-ext@lists.linux.dev, stable@vger.kernel.org, linux-kernel@vger.kernel.org
Message-ID: <20260513130111.689740-1-arighi@nvidia.com>

From: Tejun Heo <tj@kernel.org>

commit da2d81b4118a74e65d2335e221a38d665902a98c upstream.

bypass_lb_cpu() transfers tasks between per-CPU bypass DSQs without
migrating them - task_cpu() only updates when the donee later consumes the
task via move_remote_task_to_local_dsq(). If the LB timer fires again before
consumption and the new DSQ becomes a donor, @p is still on the previous CPU
and task_rq(@p) != donor_rq. @p can't be moved without its own rq locked.

Skip such tasks.

Fixes: 95d1df610cdc ("sched_ext: Implement load balancer for bypass mode")
Cc: stable@vger.kernel.org # v6.19+
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
[ arighi: replace donor_rq with rq, not present in v7.0.y ]
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/sched/ext.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4010,6 +4010,15 @@ resume:
 		if (cpumask_empty(donee_mask))
 			break;
 
+		/*
+		 * If an earlier pass placed @p on @donor_dsq from a different
+		 * CPU and the donee hasn't consumed it yet, @p is still on the
+		 * previous CPU and task_rq(@p) != @rq. @p can't be moved
+		 * without its rq locked. Skip.
+		 */
+		if (task_rq(p) != rq)
+			continue;
+
 		donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr);
 		if (donee >= nr_cpu_ids)
 			continue;


Patches currently in stable-queue which might be from arighi@nvidia.com are

queue-7.0/sched_ext-use-hk_type_domain_boot-to-detect-isolcpus-domain-isolation.patch
queue-7.0/sched_ext-skip-tasks-with-stale-task_rq-in-bypass_lb_cpu.patch