6.12-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo tj@kernel.org
[ Upstream commit f5e1e5ec204da11fa87fdf006d451d80ce06e118 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/ext.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -1682,6 +1682,14 @@ static void local_dsq_post_enq(struct sc 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; @@ -2259,6 +2267,8 @@ static void move_local_task_to_local_dsq
dsq_mod_nr(dst_dsq, 1); p->scx.dsq = dst_dsq; + + local_dsq_post_enq(dst_dsq, p, enq_flags); }
#ifdef CONFIG_SMP