[PATCH] cpu/hotplug: dont offline the last non-isolated CPU

yang.yang29
2023-09-16T02:38:27Z

From: Ran Xiaokai <ran.xiaokai@zte.com.cn>

If system has some isolate cpus with "isolcpus=" parameter,
and user try to offline all the non-isolated CPUs, kernel will
first report a warning and then panic when taking the last
non-isolated CPU offline.

Kernel should not panic when user managing CPUs with this
meaningless behavior, so we add a check for this, which
prevent user taking the last non-isolated CPU offline.

[ 19.415123] WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408
[ 19.430451] Call trace:
[ 19.430792] build_sched_domains+0x120c/0x1408
[ 19.431334] partition_sched_domains_locked+0x234/0x880
[ 19.431878] rebuild_sched_domains_locked+0x37c/0x798
[ 19.432436] rebuild_sched_domains+0x30/0x58
[ 19.432902] cpuset_hotplug_workfn+0x2a8/0x930
[ 19.433383] process_scheduled_works+0x178/0x3e0
[ 19.433878] worker_thread+0x174/0x2f0
[ 19.435204] ---[ end trace 0000000000000000 ]---
[ 19.438650] Unable to handle kernel paging request at virtual address fffe80027ab37080
[ 19.456414] partition_sched_domains_locked+0x318/0x880
[ 19.456899] rebuild_sched_domains_locked+0x37c/0x798
[ 19.457361] rebuild_sched_domains+0x30/0x58
[ 19.457761] cpuset_hotplug_workfn+0x2a8/0x930
[ 19.458175] process_scheduled_works+0x178/0x3e0
[ 19.458599] worker_thread+0x174/0x2f0
[ 19.458948] kthread+0x10c/0x128
[ 19.459268] ret_from_fork+0x10/0x20
[ 19.459728] Code: 1a850042 b9441883 f862dae0 8b000021 (f945003b)

Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Cc: Xuexin Jiang <jiang.xuexin@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
---
kernel/cpu.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6de7c6bb74ee..09ecc19d2999 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1502,6 +1502,7 @@ static long __cpu_down_maps_locked(void *arg)
static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
struct cpu_down_work work = { .cpu = cpu, .target = target, };
+ struct cpumask tmp_mask;

/*
* If the platform does not support hotplug, report it explicitly to
@@ -1512,11 +1513,16 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
if (cpu_hotplug_disabled)
return -EBUSY;

+ /*
+ * Ensure the last non-isolated CPU is not offlined.
+ */
+ cpumask_and(&tmp_mask, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
+
/*
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
*/
- cpu = cpumask_any_but(cpu_online_mask, cpu);
+ cpu = cpumask_any_but(&tmp_mask, cpu);
if (cpu >= nr_cpu_ids)
return -EBUSY;
return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
--
2.15.2