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

[Vasily Averin <vvs@virtuozzo.com>]

On 7/20/21 10:26 PM, Shakeel Butt wrote:
> On Mon, Jul 19, 2021 at 3:44 AM Vasily Averin <vvs@virtuozzo.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@virtuozzo.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.

Could you please elaborate?
From my point of view active_memcg is paired with set_active_memcg() and is not related to this case.
active_memcg uses memcg that was set by set_active_memcg(), either from int_active_memcg per-cpu pointer
or from current->active_memcg pointer.
I'm agree, it in case of disabled BH it is incorrect to use int_active_memcg, 
we still can use current->active_memcg. However it isn't a problem, 
memcg will be properly provided in both cases.

I think it's better to fix set_active_memcg/active_memcg by separate patch.

Am I missed something perhaps?

Thank you,
	Vasily Averin