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Subject: Re: [PATCH v3] debugobjects: install CPU hotplug callback
To:     qiang.zhang@windriver.com, tglx@linutronix.de, mingo@kernel.org,
        elver@google.com
Cc:     linux-kernel@vger.kernel.org
References: <20200908062709.11441-1-qiang.zhang@windriver.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <3bcdacd0-10c4-78c0-6e63-a73811a0ced6@redhat.com>
Date:   Tue, 8 Sep 2020 14:23:33 -0400
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On 9/8/20 2:27 AM, qiang.zhang@windriver.com wrote:
> From: Zqiang <qiang.zhang@windriver.com>
>
> 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.
>
> Signed-off-by: Zqiang <qiang.zhang@windriver.com>
> ---
>   v1->v2:
>   Modify submission information.
>
>   v2->v3:
>   In CPU hotplug callback func, add clear percpu pool "obj_free" operation.
>   capitalize 'CPU', and use shorter preprocessor sequence.
>
>   include/linux/cpuhotplug.h |  1 +
>   lib/debugobjects.c         | 24 ++++++++++++++++++++++++
>   2 files changed, 25 insertions(+)
>
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 3215023d4852..0c39d57e5342 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..bb69a02c3e7b 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 +434,24 @@ static void free_object(struct debug_obj *obj)
>   	}
>   }
>   
> +#ifdef 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);
> +	}
> +	percpu_pool->obj_free = 0;

For pointer, it is better to use NULL for clarity.

Cheers,
Longman

> +
> +	return 0;
> +}
> +#endif
> +
>   /*
>    * We run out of memory. That means we probably have tons of objects
>    * allocated.
> @@ -1367,6 +1386,11 @@ void __init debug_objects_mem_init(void)
>   	} else
>   		debug_objects_selftest();
>   
> +#ifdef CONFIG_HOTPLUG_CPU
> +	cpuhp_setup_state_nocalls(CPUHP_DEBUG_OBJ_DEAD, "object:offline", NULL,
> +					object_cpu_offline);
> +#endif
> +
>   	/*
>   	 * Increase the thresholds for allocating and freeing objects
>   	 * according to the number of possible CPUs available in the system.