From 50349893930ab4ac29465abf9c9791c5b34a3210 Mon Sep 17 00:00:00 2001
From: Cyril Hrubis <chrubis@suse.cz>
Date: Wed, 2 Aug 2023 17:19:06 +0200
Subject: [PATCH] sched/rt: sysctl_sched_rr_timeslice show default timeslice
 after reset
Patch-mainline: v6.6-rc1
Git-commit: c1fc6484e1fb7cc2481d169bfef129a1b0676abe
References: bsc#1220176

commit c1fc6484e1fb7cc2481d169bfef129a1b0676abe upstream.

The sched_rr_timeslice can be reset to default by writing value that is
<= 0. However after reading from this file we always got the last value
written, which is not useful at all.

$ echo -1 > /proc/sys/kernel/sched_rr_timeslice_ms
$ cat /proc/sys/kernel/sched_rr_timeslice_ms
-1

Fix this by setting the variable that holds the sysctl file value to the
jiffies_to_msecs(RR_TIMESLICE) in case that <= 0 value was written.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Tested-by: Petr Vorel <pvorel@suse.cz>
Cc: Mahmoud Adam <mngyadam@amazon.com>
Link: https://lore.kernel.org/r/20230802151906.25258-3-chrubis@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ pvorel: backported 50349893930ab4ac29465abf9c9791c5b34a3210 from stable-5.15.150 ]
---
 kernel/sched/rt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7045595aacac..2481219100af 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2883,6 +2883,9 @@ int sched_rr_handler(struct ctl_table *table, int write, void *buffer,
 		sched_rr_timeslice =
 			sysctl_sched_rr_timeslice <= 0 ? RR_TIMESLICE :
 			msecs_to_jiffies(sysctl_sched_rr_timeslice);
+
+		if (sysctl_sched_rr_timeslice <= 0)
+			sysctl_sched_rr_timeslice = jiffies_to_msecs(RR_TIMESLICE);
 	}
 	mutex_unlock(&mutex);
 
-- 
2.35.3