linux-kernel - [PATCH] sched: Have BUG_ON() check if linker sched classes don't line up correctly

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Message-ID: <20200619180219.0d558512@oasis.local.home>
Date:   Fri, 19 Jun 2020 18:02:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, philip.li@...el.com,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>
Subject: [PATCH] sched: Have BUG_ON() check if linker sched classes don't
 line up correctly

From: Steven Rostedt (VMware) <rostedt@...dmis.org>

If the sched_class structures do not match how the compiler thinks they
are in an array, it can cause hard to debug bugs. Change the BUG_ON()
from making sure each of the sched classes are in the proper order, to
also making sure they are off by the proper amount.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7ad864dc3ac5..876d7ecdab52 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6635,12 +6635,13 @@ void __init sched_init(void)
 	unsigned long ptr = 0;
 	int i;
 
-	BUG_ON(&idle_sched_class > &fair_sched_class ||
-		&fair_sched_class > &rt_sched_class ||
-		&rt_sched_class > &dl_sched_class);
+	/* Make sure the linker didn't screw up */
+	BUG_ON(&idle_sched_class + 1 != &fair_sched_class ||
+		&fair_sched_class + 1 != &rt_sched_class ||
+		&rt_sched_class + 1 != &dl_sched_class);
 
 #ifdef CONFIG_SMP
-	BUG_ON(&dl_sched_class > &stop_sched_class);
+	BUG_ON(&dl_sched_class + 1 != &stop_sched_class);
 #endif
 
 	wait_bit_init();