[PATCH 6.12 063/122] sched_ext: keep running prev when prev->scx.slice != 0

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Henry Huang <henry.hj@antgroup.com>

[ Upstream commit 30dd3b13f9de612ef7328ccffcf1a07d0d40ab51 ]

When %SCX_OPS_ENQ_LAST is set and prev->scx.slice != 0,
@prev will be dispacthed into the local DSQ in put_prev_task_scx().
However, pick_task_scx() is executed before put_prev_task_scx(),
so it will not pick @prev.
Set %SCX_RQ_BAL_KEEP in balance_one() to ensure that pick_task_scx()
can pick @prev.

Signed-off-by: Henry Huang <henry.hj@antgroup.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/sched/ext.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index f928a67a07d29..4c4681cb9337b 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2630,6 +2630,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
 {
 	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
 	bool prev_on_scx = prev->sched_class == &ext_sched_class;
+	bool prev_on_rq = prev->scx.flags & SCX_TASK_QUEUED;
 	int nr_loops = SCX_DSP_MAX_LOOPS;
 
 	lockdep_assert_rq_held(rq);
@@ -2662,8 +2663,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
 		 * See scx_ops_disable_workfn() for the explanation on the
 		 * bypassing test.
 		 */
-		if ((prev->scx.flags & SCX_TASK_QUEUED) &&
-		    prev->scx.slice && !scx_rq_bypassing(rq)) {
+		if (prev_on_rq && prev->scx.slice && !scx_rq_bypassing(rq)) {
 			rq->scx.flags |= SCX_RQ_BAL_KEEP;
 			goto has_tasks;
 		}
@@ -2696,6 +2696,10 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
 
 		flush_dispatch_buf(rq);
 
+		if (prev_on_rq && prev->scx.slice) {
+			rq->scx.flags |= SCX_RQ_BAL_KEEP;
+			goto has_tasks;
+		}
 		if (rq->scx.local_dsq.nr)
 			goto has_tasks;
 		if (consume_global_dsq(rq))
@@ -2721,8 +2725,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
 	 * Didn't find another task to run. Keep running @prev unless
 	 * %SCX_OPS_ENQ_LAST is in effect.
 	 */
-	if ((prev->scx.flags & SCX_TASK_QUEUED) &&
-	    (!static_branch_unlikely(&scx_ops_enq_last) ||
+	if (prev_on_rq && (!static_branch_unlikely(&scx_ops_enq_last) ||
 	     scx_rq_bypassing(rq))) {
 		rq->scx.flags |= SCX_RQ_BAL_KEEP;
 		goto has_tasks;
-- 
2.39.5