linux-kernel - Re: [PATCH] mm, slub: add cpus_read_lock/unlock() for slab_mem_going_offline

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Message-ID: <ef944ea5-c3cb-24e5-1ff8-b8e1008fa6ed@redhat.com>
Date:   Mon, 16 Aug 2021 10:04:13 +0200
From:   David Hildenbrand <david@...hat.com>
To:     qiang.zhang@...driver.com, vbabka@...e.cz,
        akpm@...ux-foundation.org, sfr@...b.auug.org.au
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, slub: add cpus_read_lock/unlock() for
 slab_mem_going_offline_callback()

On 16.08.21 09:46, qiang.zhang@...driver.com wrote:
> From: "Qiang.Zhang" <qiang.zhang@...driver.com>
> 
> The flush_all_cpus_locked() should be called with cpus_read_lock/unlock(),
> ensure flush_cpu_slab() can be executed on schedule_on CPU.
> 
> Fixes: 1c84f3c91640 ("mm, slub: fix memory and cpu hotplug related lock ordering issues")

Which branch contains this commit? At least not linux.git or linux-next

> Signed-off-by: Qiang.Zhang <qiang.zhang@...driver.com>
> ---
>   mm/slub.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 5543d57cb128..cf3f93abbd3e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4593,12 +4593,14 @@ static int slab_mem_going_offline_callback(void *arg)
>   {
>   	struct kmem_cache *s;
>   
> +	cpus_read_lock();
>   	mutex_lock(&slab_mutex);
>   	list_for_each_entry(s, &slab_caches, list) {
>   		flush_all_cpus_locked(s);
>   		__kmem_cache_do_shrink(s);
>   	}
>   	mutex_unlock(&slab_mutex);
> +	cpus_read_unlock();
>   
>   	return 0;
>   }
> 

Memory notifiers are getting called from online_pages()/offline_pages(), 
where we call memory_notify(MEM_GOING_OFFLINE, &arg) under 
mem_hotplug_begin().

mem_hotplug_begin() does a cpus_read_lock().

How does this even work or against which branch is this?

-- 
Thanks,

David / dhildenb