Re: [PATCH memcg] memcg: prohibit unconditional exceeding the limit of dying tasks

[Vasily Averin]

On 9/10/21 4:04 PM, Tetsuo Handa wrote:
> On 2021/09/10 21:39, Vasily Averin wrote:
>> The kernel currently allows dying tasks to exceed the memcg limits.
>> The allocation is expected to be the last one and the occupied memory
>> will be freed soon.
>> This is not always true because it can be part of the huge vmalloc
>> allocation. Allowed once, they will repeat over and over again.
>> Moreover lifetime of the allocated object can differ from
>> In addition the lifetime of the dying task.
> 
> Can't we add fatal_signal_pending(current) test to vmalloc() loop?

1) this has been done in the past but has been reverted later.
2) any vmalloc changes will affect non-memcg allocations too.
 If we're doing memcg-related checks it's better to do it in one place.
3) it is not vmalloc-only issue. Huge number of  kmalloc page allocations 
from N concurrent threads will lead to the same problem. 

>> Multiple such allocations running concurrently can not only overuse
>> the memcg limit, but can lead to a global out of memory and,
>> in the worst case, cause the host to panic.
>>
>> Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>