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

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Date:   Tue, 30 Aug 2022 20:59:32 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Maurizio Lombardi <mlombard@...hat.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, linux-mm <linux-mm@...ck.org>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, tglx@...utronix.de
Subject: Re: [PATCH RFC] mm: slub: fix flush_cpu_slab()/__free_slab()
 invocations in task context.

On 2022-08-30 17:48:06 [+0200], Maurizio Lombardi wrote:
> Hmm, this is not good indeed. I guess I should have used for_each_online_cpu()
> instead of on_each_cpu_cond().

But you must not invoked that function cross-CPU since the code expects
to access the per-CPU variables always from the local-CPU.

> >
> > Couldn't we instead use a workqueue with that WQ_MEM_RECLAIM bit? It may
> > reclaim memory after all ;)
> 
> That should also fix it, do you think it would be ok to allocate a workqueue in
> in kmem_cache_init() ?

I guess so. There is probably none that is already available.

> Thanks,
> Maurizio

Sebastian