[tip: sched/core] sched/debug: Stop and start server based on if it was active

[tip-bot2 for Joel Fernandes]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     68ec89d0e99156803bdea3c986c0198624e40ea2
Gitweb:        https://git.kernel.org/tip/68ec89d0e99156803bdea3c986c0198624e40ea2
Author:        Joel Fernandes <joelagnelf@xxxxxxxxxx>
AuthorDate:    Mon, 26 Jan 2026 10:59:01 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 03 Feb 2026 12:04:17 +01:00

sched/debug: Stop and start server based on if it was active

Currently the DL server interface for applying parameters checks
CFS-internals to identify if the server is active. This is error-prone
and makes it difficult when adding new servers in the future.

Fix it, by using dl_server_active() which is also used by the DL server
code to determine if the DL server was started.

Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Reviewed-by: Andrea Righi <arighi@xxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Tested-by: Christian Loehle <christian.loehle@xxxxxxx>
Link: https://patch.msgid.link/20260126100050.3854740-4-arighi@xxxxxxxxxx
---
 kernel/sched/debug.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index ed9254d..41e3895 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -348,6 +348,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 		return err;
 
 	scoped_guard (rq_lock_irqsave, rq) {
+		bool is_active;
+
 		runtime  = rq->fair_server.dl_runtime;
 		period = rq->fair_server.dl_period;
 
@@ -370,8 +372,11 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 			return  -EINVAL;
 		}
 
-		update_rq_clock(rq);
-		dl_server_stop(&rq->fair_server);
+		is_active = dl_server_active(&rq->fair_server);
+		if (is_active) {
+			update_rq_clock(rq);
+			dl_server_stop(&rq->fair_server);
+		}
 
 		retval = dl_server_apply_params(&rq->fair_server, runtime, period, 0);
 
@@ -379,7 +384,7 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 			printk_deferred("Fair server disabled in CPU %d, system may crash due to starvation.\n",
 					cpu_of(rq));
 
-		if (rq->cfs.h_nr_queued)
+		if (is_active && runtime)
 			dl_server_start(&rq->fair_server);
 
 		if (retval < 0)