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Date:   Mon, 14 Jun 2021 13:16:19 +0200
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jann Horn <jannh@google.com>
Subject: Re: [RFC v2 33/34] mm, slub: use migrate_disable() on PREEMPT_RT
Message-ID: <20210614111619.l3ral7tt2wasvlb4@linutronix.de>
References: <20210609113903.1421-1-vbabka@suse.cz>
 <20210609113903.1421-34-vbabka@suse.cz>
 <c553c26f-1f9c-e5ab-b71b-b2b5eeb59ad2@suse.cz>
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On 2021-06-14 13:07:14 [+0200], Vlastimil Babka wrote:
> > +#ifdef CONFIG_PREEMPT_RT
> > +#define slub_get_cpu_ptr(var)	get_cpu_ptr(var)
> > +#define slub_put_cpu_ptr(var)	put_cpu_ptr(var)
> 
> After Mel's report and bisect pointing to this patch, I realized I got the
> #ifdef wrong and it should be #ifnded

So if you got the ifdef wrong (and kept everything as-is) then you
tested the RT version on !RT. migrate_disable() behaves on !RT as on RT.
As per changelog you don't use migrate_disable() unconditionally because
it increases the overhead on !RT.
I haven't looked at the series and I have just this tiny question: why
did migrate_disable() crash for Mel on !RT and why do you expect that it
does not happen on PREEMPT_RT?

Sebastian