The patch below does not apply to the 6.12-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-6.12.y git checkout FETCH_HEAD git cherry-pick -x f5e1e5ec204da11fa87fdf006d451d80ce06e118 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122951-giggle-reveler-2e6b@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From f5e1e5ec204da11fa87fdf006d451d80ce06e118 Mon Sep 17 00:00:00 2001 From: Tejun Heo tj@kernel.org Date: Thu, 11 Dec 2025 15:45:04 -1000 Subject: [PATCH] sched_ext: Fix missing post-enqueue handling in move_local_task_to_local_dsq()

move_local_task_to_local_dsq() is used when moving a task from a non-local DSQ to a local DSQ on the same CPU. It directly manipulates the local DSQ without going through dispatch_enqueue() and was missing the post-enqueue handling that triggers preemption when SCX_ENQ_PREEMPT is set or the idle task is running.

The function is used by move_task_between_dsqs() which backs scx_bpf_dsq_move() and may be called while the CPU is busy.

Add local_dsq_post_enq() call to move_local_task_to_local_dsq(). As the dispatch path doesn't need post-enqueue handling, add SCX_RQ_IN_BALANCE early exit to keep consume_dispatch_q() behavior unchanged and avoid triggering unnecessary resched when scx_bpf_dsq_move() is used from the dispatch path.

Fixes: 4c30f5ce4f7a ("sched_ext: Implement scx_bpf_dispatch[_vtime]_from_dsq()") Cc: stable@vger.kernel.org # v6.12+ Reviewed-by: Andrea Righi arighi@nvidia.com Reviewed-by: Emil Tsalapatis emil@etsalapatis.com Signed-off-by: Tejun Heo tj@kernel.org

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index c78efa99406f..695503a2f7d1 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -988,6 +988,14 @@ static void local_dsq_post_enq(struct scx_dispatch_q *dsq, struct task_struct *p struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); bool preempt = false;

+ /* + * If @rq is in balance, the CPU is already vacant and looking for the + * next task to run. No need to preempt or trigger resched after moving + * @p into its local DSQ. + */ + if (rq->scx.flags & SCX_RQ_IN_BALANCE) + return; + if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && rq->curr->sched_class == &ext_sched_class) { rq->curr->scx.slice = 0; @@ -1636,6 +1644,8 @@ static void move_local_task_to_local_dsq(struct task_struct *p, u64 enq_flags,

dsq_mod_nr(dst_dsq, 1); p->scx.dsq = dst_dsq; + + local_dsq_post_enq(dst_dsq, p, enq_flags); }

/**