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

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Message-ID: <20171002112051.uk4gyrtygfgtvp5g@dhcp22.suse.cz>
Date:   Mon, 2 Oct 2017 13:20:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     Yang Shi <yang.s@...baba-inc.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2 v8] oom: capture unreclaimable slab info in oom
 message

On Thu 28-09-17 13:36:57, Tetsuo Handa wrote:
> On 2017/09/28 6:46, Yang Shi wrote:
> > Changelog v7 —> v8:
> > * Adopted Michal’s 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
SUSE Labs