sched: Restructure sched_class order sanity checks in sched_init()

Currently, sched_init() checks that the sched_class'es are in the expected
order by testing each adjacency which is a bit brittle and makes it
cumbersome to add optional sched_class'es. Instead, let's verify whether
they're in the expected order using sched_class_above() which is what
matters.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: David Vernet <dvernet@meta.com>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0935f9d..b4d4551 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8164,12 +8164,12 @@ void __init sched_init(void)
        int i;
 
        /* Make sure the linker didn't screw up */
-       BUG_ON(&idle_sched_class != &fair_sched_class + 1 ||
-              &fair_sched_class != &rt_sched_class + 1 ||
-              &rt_sched_class   != &dl_sched_class + 1);
 #ifdef CONFIG_SMP
-       BUG_ON(&dl_sched_class != &stop_sched_class + 1);
+       BUG_ON(!sched_class_above(&stop_sched_class, &dl_sched_class));
 #endif
+       BUG_ON(!sched_class_above(&dl_sched_class, &rt_sched_class));
+       BUG_ON(!sched_class_above(&rt_sched_class, &fair_sched_class));
+       BUG_ON(!sched_class_above(&fair_sched_class, &idle_sched_class));
 
        wait_bit_init();