Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom message

From: Michal Hocko
Date: Mon Oct 02 2017 - 07:20:59 EST

On Thu 28-09-17 13:36:57, Tetsuo Handa wrote:
> On 2017/09/28 6:46, Yang Shi wrote:
> > Changelog v7 â> v8:
> > * Adopted Michalâs suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path.
> Holding slab_mutex inside dump_unreclaimable_slab() was refrained since V2
> because there are
> mutex_lock(&slab_mutex);
> kmalloc(GFP_KERNEL);
> mutex_unlock(&slab_mutex);
> users. If we call dump_unreclaimable_slab() for non OOM panic path, aren't we
> introducing a risk of crash (i.e. kernel panic) for regular OOM path?

yes we are

> We can try mutex_trylock() from dump_unreclaimable_slab() at best.
> But it is still remaining unsafe, isn't it?

using the trylock sounds like a reasonable compromise.
Michal Hocko