linux-kernel - Re: [rfc/patch] mm/slub: restore/expand unfreeze

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Message-ID: <6c0e20dd84084036d5068e445746c3ed7e82ec4b.camel@gmx.de>
Date:   Sat, 10 Jul 2021 03:12:45 +0200
From:   Mike Galbraith <efault@....de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     linux-rt-users@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local
 exclusion scope

On Fri, 2021-07-09 at 21:28 +0200, Thomas Gleixner wrote:
> On Fri, Jul 09 2021 at 07:21, Mike Galbraith wrote:
> > static bool has_cpu_slab(int cpu, struct kmem_cache *s)
> > @@ -2632,8 +2636,11 @@ static int slub_cpu_dead(unsigned int cp
> >  	struct kmem_cache *s;
> >
> >  	mutex_lock(&slab_mutex);
> > -	list_for_each_entry(s, &slab_caches, list)
> > +	list_for_each_entry(s, &slab_caches, list) {
> > +		local_lock(&s->cpu_slab->lock);
>
> This one is odd. It locks the cpu_slab lock of the CPU which runs
> thiscallback and then flushes the slab of the dead CPU.

That spot I put back only because it used to exist, ergo I documented
it as an afterthought.  Yeah, it clearly has nada to do with the
explosions, those were stopped by the other two as previously reported.

	-Mike