linux-kernel - Re: [PATCH] x86/sgx: Set active memcg prior to shmem allocation

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Message-ID: <CALvZod40TpW0rX1jvj6GZWtr=nscJFkw_zdvZjbh7GPgd8pLWQ@mail.gmail.com>
Date:   Wed, 18 May 2022 22:43:05 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc:     linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Linux-MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/sgx: Set active memcg prior to shmem allocation

(Fixing the CC list and sending again)

On Tue, May 17, 2022 at 09:47:13AM -0700, Kristen Carlson Accardi wrote:
>
[...]
> +int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
> +                        struct sgx_backing *backing)
> +{
> +     struct mem_cgroup *old_memcg;
> +     int ret;
> +
> +     old_memcg = sgx_encl_set_active_memcg(encl);

This function is leaking memcg reference. Please change
sgx_encl_set_active_memcg() to sgx_encl_get_mem_cgroup() or something
which will return the memcg with the refcount elevated. Then use
set_active_memcg(returned_memcg) here.

> +
> +     ret = sgx_encl_get_backing(encl, page_index, backing);
> +
> +     set_active_memcg(old_memcg);

mem_cgroup_put(returned_memcg) here.

> +
> +     return ret;
> +}