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Message-ID: <4fa0e9016f746e070150f6db78202d744a3f9c4c.camel@gmx.de>
Subject: Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations
 __free_slab() invocations out of IRQ context
From:   Mike Galbraith <efault@gmx.de>
To:     Vlastimil Babka <vbabka@suse.cz>,
        Qian Cai <quic_qiancai@quicinc.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Jann Horn <jannh@google.com>
Date:   Tue, 10 Aug 2021 03:07:01 +0200
In-Reply-To: <7d9ac614-f18e-de5d-2d47-f92e618d76fc@suse.cz>
References: <20210805152000.12817-1-vbabka@suse.cz>
         <20210805152000.12817-30-vbabka@suse.cz>
         <0b36128c-3e12-77df-85fe-a153a714569b@quicinc.com>
         <6e3bb54fdf7208f3f86a5d31e1ef2a576d8e7e37.camel@gmx.de>
         <7d9ac614-f18e-de5d-2d47-f92e618d76fc@suse.cz>
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On Mon, 2021-08-09 at 22:08 +0200, Vlastimil Babka wrote:
> On 8/9/2021 8:44 PM, Mike Galbraith wrote:
> > >
> > > slab_mutex -> flush_lock
> >
> > Bugger.=C2=A0 That chain ending with cpu_hotplug_lock makes slub_cpu_d=
ead()
> > taking slab_mutex a non-starter for cpu hotplug as well.=C2=A0 It's
> > established early by kernel_init_freeable()..kmem_cache_destroy() as
> > well as by slab_mem_going_offline_callback().
>
> I suck at reading the lockdep splats, so I don't see yet how the "existi=
ng
> reverse order" occurs - I do understand the order in the "lsbug".
> What I also wonder is why didn't this occur also in the older RT trees w=
ith this
> patch.

Apparently (oops) nobody got around to hotplug+lockdep testing, RT or
otherwise.  I know I didn't, goldfish like attention span being used up
by explosion testing ;-)

	-Mike