netdev - Re: [PATCH v5 02/16] memcg: enable accounting for IP address and routing-related objects

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Date:   Tue, 20 Jul 2021 12:26:48 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 02/16] memcg: enable accounting for IP address and
 routing-related objects

On Mon, Jul 19, 2021 at 3:44 AM Vasily Averin <vvs@...tuozzo.com> wrote:
>
> An netadmin inside container can use 'ip a a' and 'ip r a'
> to assign a large number of ipv4/ipv6 addresses and routing entries
> and force kernel to allocate megabytes of unaccounted memory
> for long-lived per-netdevice related kernel objects:
> 'struct in_ifaddr', 'struct inet6_ifaddr', 'struct fib6_node',
> 'struct rt6_info', 'struct fib_rules' and ip_fib caches.
>
> These objects can be manually removed, though usually they lives
> in memory till destroy of its net namespace.
>
> It makes sense to account for them to restrict the host's memory
> consumption from inside the memcg-limited container.
>
> One of such objects is the 'struct fib6_node' mostly allocated in
> net/ipv6/route.c::__ip6_ins_rt() inside the lock_bh()/unlock_bh() section:
>
>  write_lock_bh(&table->tb6_lock);
>  err = fib6_add(&table->tb6_root, rt, info, mxc);
>  write_unlock_bh(&table->tb6_lock);
>
> In this case it is not enough to simply add SLAB_ACCOUNT to corresponding
> kmem cache. The proper memory cgroup still cannot be found due to the
> incorrect 'in_interrupt()' check used in memcg_kmem_bypass().
>
> Obsoleted in_interrupt() does not describe real execution context properly.
> From include/linux/preempt.h:
>
>  The following macros are deprecated and should not be used in new code:
>  in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled
>
> To verify the current execution context new macro should be used instead:
>  in_task()      - We're in task context
>
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
> ---
>  mm/memcontrol.c      | 2 +-
>  net/core/fib_rules.c | 4 ++--
>  net/ipv4/devinet.c   | 2 +-
>  net/ipv4/fib_trie.c  | 4 ++--
>  net/ipv6/addrconf.c  | 2 +-
>  net/ipv6/ip6_fib.c   | 4 ++--
>  net/ipv6/route.c     | 2 +-
>  7 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ae1f5d0..1bbf239 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -968,7 +968,7 @@ static __always_inline bool memcg_kmem_bypass(void)
>                 return false;
>
>         /* Memcg to charge can't be determined. */
> -       if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD))
> +       if (!in_task() || !current->mm || (current->flags & PF_KTHREAD))
>                 return true;
>
>         return false;

Can you please also change in_interrupt() in active_memcg() as well?
There are other unrelated in_interrupt() in that file but the one in
active_memcg() should be coupled with this change.