sched/core: Add assertions to QUEUE_CLASS

Add some checks to the sched_change pattern to validate assumptions
around changing classes.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251127154725.771691954@infradead.org

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 41ba0be169117442680bf79dd6440d3bf03f6b69..4479f7d1fdfb60742705ba4001debeca1e7a09de 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10782,6 +10782,7 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int
 
        *ctx = (struct sched_change_ctx){
                .p = p,
+               .class = p->sched_class,
                .flags = flags,
                .queued = task_on_rq_queued(p),
                .running = task_current_donor(rq, p),
@@ -10812,6 +10813,11 @@ void sched_change_end(struct sched_change_ctx *ctx)
 
        lockdep_assert_rq_held(rq);
 
+       /*
+        * Changing class without *QUEUE_CLASS is bad.
+        */
+       WARN_ON_ONCE(p->sched_class != ctx->class && !(ctx->flags & ENQUEUE_CLASS));
+
        if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switching_to)
                p->sched_class->switching_to(rq, p);
 
@@ -10823,6 +10829,13 @@ void sched_change_end(struct sched_change_ctx *ctx)
        if (ctx->flags & ENQUEUE_CLASS) {
                if (p->sched_class->switched_to)
                        p->sched_class->switched_to(rq, p);
+
+               /*
+                * If this was a degradation in class someone should have set
+                * need_resched by now.
+                */
+               WARN_ON_ONCE(sched_class_above(ctx->class, p->sched_class) &&
+                            !test_tsk_need_resched(p));
        } else {
                p->sched_class->prio_changed(rq, p, ctx->prio);
        }

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 67cff7d6cc2ff1d4d7f13bdea8e49f7bf472227a..a40582d5b28820b40d81bfcd0af27e4e4cfcf011 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3968,6 +3968,7 @@ extern void balance_callbacks(struct rq *rq, struct balance_callback *head);
 struct sched_change_ctx {
        u64                     prio;
        struct task_struct      *p;
+       const struct sched_class *class;
        int                     flags;
        bool                    queued;
        bool                    running;