Re: [PATCH] memcg: account security cred as well to kmemcg

From: Michal Hocko <mhocko@kernel.org>
To: Shakeel Butt <shakeelb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Roman Gushchin <guro@fb.com>,
	linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: account security cred as well to kmemcg
Date: Fri, 6 Dec 2019 09:17:10 +0100	[thread overview]
Message-ID: <20191206081710.GK28317@dhcp22.suse.cz> (raw)
In-Reply-To: <20191205223721.40034-1-shakeelb@google.com>

On Thu 05-12-19 14:37:21, Shakeel Butt wrote:
> The cred_jar kmem_cache is already memcg accounted in the current
> kernel but cred->security is not. Account cred->security to kmemcg.
> 
> Recently we saw high root slab usage on our production and on further
> inspection, we found a buggy application leaking processes. Though that
> buggy application was contained within its memcg but we observe much
> more system memory overhead, couple of GiBs, during that period. This
> overhead can adversely impact the isolation on the system. One of source
> of high overhead, we found was cred->secuity objects.

I am not familiar with this area much. What is the timelife of these
objects? Do they go away with a task allocating them?

> Signed-off-by: Shakeel Butt <shakeelb@google.com>
>
> ---
>  kernel/cred.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/cred.c b/kernel/cred.c
> index c0a4c12d38b2..9ed51b70ed80 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -223,7 +223,7 @@ struct cred *cred_alloc_blank(void)
>  	new->magic = CRED_MAGIC;
>  #endif
>  
> -	if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
> +	if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
>  		goto error;
>  
>  	return new;
> @@ -282,7 +282,7 @@ struct cred *prepare_creds(void)
>  	new->security = NULL;
>  #endif
>  
> -	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
> +	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
>  		goto error;
>  	validate_creds(new);
>  	return new;
> @@ -715,7 +715,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
>  #ifdef CONFIG_SECURITY
>  	new->security = NULL;
>  #endif
> -	if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
> +	if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
>  		goto error;
>  
>  	put_cred(old);
> -- 
> 2.24.0.393.g34dc348eaf-goog
> 

-- 
Michal Hocko
SUSE Labs