[PATCH v5 05/14] sched/deadline: Return EBUSY if dl_bw_cpus is zero

Joel Fernandes
2025-06-20T20:32:57Z

Hotplugged CPUs coming online do an enqueue but are not a part of any
root domain containing cpu_active() CPUs. So in this case, don't mess
with accounting and we can retry later. Without this patch, we see
crashes with sched_ext selftest's hotplug test due to divide by zero.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
kernel/sched/deadline.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index d2eb31b45ba9..749c1453a809 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1725,7 +1725,10 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
cpus = dl_bw_cpus(cpu);
cap = dl_bw_capacity(cpu);

- if (__dl_overflow(dl_b, cap, old_bw, new_bw))
+ // Hotplugged CPUs coming online do an enqueue but are not a part of any
+ // root domain containing cpu_active() CPUs. So in this case, don't mess
+ // with accounting and we can retry later.
+ if (!cpus || __dl_overflow(dl_b, cap, old_bw, new_bw))
return -EBUSY;

if (init) {
--
2.43.0