[Devel] [PATCH rh7 2/2] exit: clear TIF_MEMDIE after exit_task_work

[Kirill Tkhai]

On 29.02.2016 18:58, Vladimir Davydov wrote:
> An mm_struct may be pinned by a file. An example is vhost-net device
> created by a qemu/kvm (see vhost_net_ioctl -> vhost_net_set_owner ->
> vhost_dev_set_owner). If such process gets OOM-killed, the reference to
> its mm_struct will only be released from exit_task_work -> ____fput ->
> __fput -> vhost_net_release -> vhost_dev_cleanup, which is called after
> exit_mmap, where TIF_MEMDIE is cleared. As a result, we can start
> selecting the next victim before giving the last one a chance to free
> its memory. In practice, this leads to killing several VMs along with
> the fattest one.

Do we have the same issue when group_leader's threads are owning the mm?
 
> https://jira.sw.ru/browse/PSBM-44683
> 
> Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
> ---
>  kernel/exit.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 1cc765b48bd7..2715dc1dc0f5 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -520,8 +520,6 @@ static void exit_mm(struct task_struct * tsk)
>  	task_unlock(tsk);
>  	mm_update_next_owner(mm);
>  	mmput(mm);
> -	if (test_thread_flag(TIF_MEMDIE))
> -		exit_oom_victim();
>  }
>  
>  /*
> @@ -819,6 +817,10 @@ void do_exit(long code)
>  	exit_fs(tsk);
>  	exit_task_namespaces(tsk);
>  	exit_task_work(tsk);
> +
> +	if (test_thread_flag(TIF_MEMDIE))
> +		exit_oom_victim();
> +
>  	check_stack_usage();
>  	exit_thread();
>  
>