sched/deadline: Reset extra_bw to max_bw when clearing root domains

dl_clear_root_domain() doesn't take into account the fact that per-rq
extra_bw variables retain values computed before root domain changes,
resulting in broken accounting.

Fix it by resetting extra_bw to max_bw before restoring back dl-servers
contributions.

Fixes: 2ff899e351643 ("sched/deadline: Rebuild root domain accounting after every update")
Reported-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@codethink.co.uk> # nuc & rock5b
Link: https://lore.kernel.org/r/20250627115118.438797-3-juri.lelli@redhat.com

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0d25553f2c178657f34ceb407d171f97811f6da2..0abffe3860e3e38c95596e8ac2d746df01114e62 100644 (file)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2924,7 +2924,14 @@ void dl_clear_root_domain(struct root_domain *rd)
        int i;
 
        guard(raw_spinlock_irqsave)(&rd->dl_bw.lock);
+
+       /*
+        * Reset total_bw to zero and extra_bw to max_bw so that next
+        * loop will add dl-servers contributions back properly,
+        */
        rd->dl_bw.total_bw = 0;
+       for_each_cpu(i, rd->span)
+               cpu_rq(i)->dl.extra_bw = cpu_rq(i)->dl.max_bw;
 
        /*
         * dl_servers are not tasks. Since dl_add_task_root_domain ignores