Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary

[Oleg Nesterov <oleg@xxxxxxxxxx>]

On 08/20, Eric W. Biederman wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1139,6 +1139,10 @@ static int exec_mmap(struct mm_struct *mm)
>  	vmacache_flush(tsk);
>  	task_unlock(tsk);
>  	if (old_mm) {
> +		mm->oom_score_adj = old_mm->oom_score_adj;
> +		mm->oom_score_adj_min = old_mm->oom_score_adj_min;
> +		if (tsk->vfork_done)
> +			mm->oom_score_adj = tsk->vfork_oom_score_adj;

too late, ->vfork_done is NULL after mm_release().

And this can race with __set_oom_adj(). Yes, the current code is racy too,
but this change adds another race, __set_oom_adj() could already observe
->mm != NULL and update mm->oom_score_adj.

Oleg.