[PATCH] sched/core: Test online status in available_idle_cpu()

Sven Schnelle
2024-04-29T05:55:13Z

The current implementation of available_idle_cpu() doesn't test
whether a possible cpu is offline. On s390 this dereferences a
NULL pointer in arch_vcpu_is_preempted() because lowcore is not
allocated for offline cpus. On x86, tracing also shows calls to
available_idle_cpu() after a cpu is disabled, but it looks like
this isn't causing any (obvious) issue. Nevertheless, add a check
and return early if the cpu isn't online.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
kernel/sched/core.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..1d9b80411594 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7434,6 +7434,9 @@ int idle_cpu(int cpu)
*/
int available_idle_cpu(int cpu)
{
+ if (!cpu_online(cpu))
+ return 0;
+
if (!idle_cpu(cpu))
return 0;

--
2.40.1