Re: 回复: [PATCH v2] debugobjects: install cpu hotplug callback

From: Ingo Molnar
Date: Fri Sep 04 2020 - 01:50:52 EST



* Zhang, Qiang <Qiang.Zhang@xxxxxxxxxxxxx> wrote:

> tglx please review.
>
> Thanks
> Qiang
> ________________________________________
> 发件人: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-owner@xxxxxxxxxxxxxxx> 代表 qiang.zhang@xxxxxxxxxxxxx <qiang.zhang@xxxxxxxxxxxxx>
> 发送时间: 2020年8月27日 13:06
> 收件人: tglx@xxxxxxxxxxxxx; longman@xxxxxxxxxx; elver@xxxxxxxxxx
> 抄送: linux-kernel@xxxxxxxxxxxxxxx
> 主题: [PATCH v2] debugobjects: install cpu hotplug callback
>
> From: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
>
> Due to cpu hotplug, it may never be online after it's offline,
> some objects in percpu pool is never free, in order to avoid
> this happening, install cpu hotplug callback, call this callback
> func to free objects in percpu pool when cpu going offline.

We capitalize 'CPU'. Also, please split this in at least two sentences.

>
> Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
> ---
> v1->v2:
> Modify submission information.
>
> include/linux/cpuhotplug.h | 1 +
> lib/debugobjects.c | 23 +++++++++++++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index a2710e654b64..2e77db655cfa 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -36,6 +36,7 @@ enum cpuhp_state {
> CPUHP_X86_MCE_DEAD,
> CPUHP_VIRT_NET_DEAD,
> CPUHP_SLUB_DEAD,
> + CPUHP_DEBUG_OBJ_DEAD,
> CPUHP_MM_WRITEBACK_DEAD,
> CPUHP_MM_VMSTAT_DEAD,
> CPUHP_SOFTIRQ_DEAD,
> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
> index fe4557955d97..50e21ed0519e 100644
> --- a/lib/debugobjects.c
> +++ b/lib/debugobjects.c
> @@ -19,6 +19,7 @@
> #include <linux/slab.h>
> #include <linux/hash.h>
> #include <linux/kmemleak.h>
> +#include <linux/cpu.h>
>
> #define ODEBUG_HASH_BITS 14
> #define ODEBUG_HASH_SIZE (1 << ODEBUG_HASH_BITS)
> @@ -433,6 +434,23 @@ static void free_object(struct debug_obj *obj)
> }
> }
>
> +#if defined(CONFIG_HOTPLUG_CPU)
> +static int object_cpu_offline(unsigned int cpu)
> +{
> + struct debug_percpu_free *percpu_pool;
> + struct hlist_node *tmp;
> + struct debug_obj *obj;
> +
> + percpu_pool = per_cpu_ptr(&percpu_obj_pool, cpu);
> + hlist_for_each_entry_safe(obj, tmp, &percpu_pool->free_objs, node) {
> + hlist_del(&obj->node);
> + kmem_cache_free(obj_cache, obj);
> + }
> +
> + return 0;
> +}
> +#endif

What happens to ->obj_free, if the CPU is brought back online? Won't it be
out of sync at that point?

> +#if defined(CONFIG_HOTPLUG_CPU)

There's a shorter preprocessor sequence for that pattern.

Thanks,

Ingo