sched_ext: Pass held rq to SCX_CALL_OP() for core_sched_before

scx_prio_less() runs from core-sched's pick_next_task() path with rq
locked but invokes ops.core_sched_before() with NULL locked_rq, leaving
scx_locked_rq_state NULL. If the BPF callback calls a kfunc that
re-acquires rq based on scx_locked_rq() - e.g. scx_bpf_cpuperf_set(cpu)
- it re-acquires the already-held rq.

Pass task_rq(a).

Fixes: 7b0888b7cc19 ("sched_ext: Implement core-sched support")
Cc: stable@vger.kernel.org # v6.12+
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 73d629559d6d11b157d55bbba247cd9199cc1860..ba977154273c1ae6e87ecca7261258778b62ba4d 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3198,7 +3198,7 @@ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
        if (sch_a == sch_b && SCX_HAS_OP(sch_a, core_sched_before) &&
            !scx_bypassing(sch_a, task_cpu(a)))
                return SCX_CALL_OP_2TASKS_RET(sch_a, core_sched_before,
-                                             NULL,
+                                             task_rq(a),
                                              (struct task_struct *)a,
                                              (struct task_struct *)b);
        else