linux-kernel - Re: [PATCH V3] mm: slub: fix flush_cpu_slab()/__free

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Date:   Tue, 20 Sep 2022 09:56:59 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Maurizio Lombardi <mlombard@...hat.com>, vbabka@...e.cz,
        linux-mm@...ck.org, rientjes@...gle.com, penberg@...nel.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] mm: slub: fix flush_cpu_slab()/__free_slab()
 invocations in task context.

On 2022-09-20 16:46:41 [+0900], Hyeonggon Yoo wrote:
> > @@ -2730,7 +2735,7 @@ static void flush_all_cpus_locked(struct kmem_cache *s)
> >  		INIT_WORK(&sfw->work, flush_cpu_slab);
> >  		sfw->skip = false;
> >  		sfw->s = s;
> > -		schedule_work_on(cpu, &sfw->work);
> > +		queue_work_on(cpu, flushwq, &sfw->work);
> 
> Hi. what happens here if flushwq failed?
> 
> I think avoiding BUG_ON() makes sense,
> but shouldn't we have fallback method?

You get an output to act on and fix. The point is that it shouldn't have
happen in the first place. With the bug_on() that early, chances are
that you never see anything but a blank screen. So with the warn_on you
get probably to see the warn_on before you get here.

Sebastian