On 05/30, Michal Hocko wrote:
>
> Make sure to not select vforked task as an oom victim by checking
> vfork_done in oom_badness.
I agree, this look like a good change to me... But.
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -176,11 +176,13 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
>
> /*
> * Do not even consider tasks which are explicitly marked oom
> - * unkillable or have been already oom reaped.
> + * unkillable or have been already oom reaped or the are in
> + * the middle of vfork
> */
> adj = (long)p->signal->oom_score_adj;
> if (adj == OOM_SCORE_ADJ_MIN ||
> - test_bit(MMF_OOM_REAPED, &p->mm->flags)) {
> + test_bit(MMF_OOM_REAPED, &p->mm->flags) ||
> + p->vfork_done) {
I don't think we can trust vfork_done != NULL.
copy_process() doesn't disallow CLONE_VFORK without CLONE_VM, so with this patch
it would be trivial to make the exploit which hides a memory hog from oom-killer.
So perhaps we need something like
bool in_vfork(p)
{
return p->vfork_done &&
p->real_parent->mm == mm;
}
task_lock() is not enough if CLONE_VM was used along with CLONE_PARENT... so this
also needs rcu_read_lock() to access ->real_parent.
Or I am totally confused?
Oleg.
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