linux-kernel - Re: [PATCH v3 5/5] percpu: scoped objcg protection

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Message-ID: <3b723bf1-830e-7f47-27ce-98f7808fbc4b@suse.cz>
Date:   Wed, 18 Oct 2023 16:23:14 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, shakeelb@...gle.com,
        Muchun Song <muchun.song@...ux.dev>,
        Dennis Zhou <dennis@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>
Subject: Re: [PATCH v3 5/5] percpu: scoped objcg protection

On 10/17/23 00:19, Roman Gushchin wrote:
> Similar to slab and kmem, switch to a scope-based protection of the
> objcg pointer to avoid.
> 
> Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@...ux.dev>
> Tested-by: Naresh Kamboju <naresh.kamboju@...aro.org>
> Acked-by: Shakeel Butt <shakeelb@...gle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Do you plan to convert also the bpf users of get_obj_cgroup_from_current()
so it could be removed?

Thanks!

> ---
>  mm/percpu.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index a7665de8485f..f53ba692d67a 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1628,14 +1628,12 @@ static bool pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
>  	if (!memcg_kmem_online() || !(gfp & __GFP_ACCOUNT))
>  		return true;
>  
> -	objcg = get_obj_cgroup_from_current();
> +	objcg = current_obj_cgroup();
>  	if (!objcg)
>  		return true;
>  
> -	if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size))) {
> -		obj_cgroup_put(objcg);
> +	if (obj_cgroup_charge(objcg, gfp, pcpu_obj_full_size(size)))
>  		return false;
> -	}
>  
>  	*objcgp = objcg;
>  	return true;
> @@ -1649,6 +1647,7 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
>  		return;
>  
>  	if (likely(chunk && chunk->obj_cgroups)) {
> +		obj_cgroup_get(objcg);
>  		chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = objcg;
>  
>  		rcu_read_lock();
> @@ -1657,7 +1656,6 @@ static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
>  		rcu_read_unlock();
>  	} else {
>  		obj_cgroup_uncharge(objcg, pcpu_obj_full_size(size));
> -		obj_cgroup_put(objcg);
>  	}
>  }
>