sched_rt_handler() unconditionally calls rebuild_sched_domains() on exit.

That means scheduler domains are rebuilt even for read-only sysctl access,
and also after writes that fail validation and roll back to the old RT
bandwidth values.

Track whether the write path completed validation and global RT/DL updates,
and rebuild scheduler domains only in that case.

Fixes: 440989c10f4e ("sched/deadline: Fix accounting after global limits change")
Cc: stable@vger.kernel.org
Signed-off-by: Joseph Salisbury <joseph.salisbury@oracle.com>
---
 kernel/sched/rt.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 906f6c656c2e..ada9249b22cd 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2871,6 +2871,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 {
 	int old_period, old_runtime;
 	static DEFINE_MUTEX(mutex);
+	bool rebuild = false;
 	int ret;
 
 	mutex_lock(&mutex);
@@ -2895,6 +2896,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 
 		sched_rt_do_global();
 		sched_dl_do_global();
+		rebuild = true;
 	}
 	if (0) {
 undo:
@@ -2908,7 +2910,8 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 	 * After changing maximum available bandwidth for DEADLINE, we need to
 	 * recompute per root domain and per cpus variables accordingly.
 	 */
-	rebuild_sched_domains();
+	if (rebuild)
+		rebuild_sched_domains();
 
 	return ret;
 }
-- 
2.47.3