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

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Date:   Mon, 9 Dec 2019 15:43:32 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Linux MM <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: account security cred as well to kmemcg

On Fri 06-12-19 08:51:21, Shakeel Butt wrote:
> On Fri, Dec 6, 2019 at 12:17 AM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > 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?
> >
> 
> Lifetime is at least the life of the process allocating them.

Thanks for the clarification! It is better to be explicit about this in
the changelog I believe because it would make a review much easier.
Accounting for objects which are not bound to a user process context is
more complex and requires much more considerations.

> > > Signed-off-by: Shakeel Butt <shakeelb@...gle.com>

With that clarification
Acked-by: Michal Hocko <mhocko@...e.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

-- 
Michal Hocko
SUSE Labs