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Date:   Tue, 10 Aug 2021 03:07:01 +0200
From:   Mike Galbraith <>
To:     Vlastimil Babka <>,
        Qian Cai <>,
        Andrew Morton <>,
        Christoph Lameter <>,
        David Rientjes <>,
        Pekka Enberg <>,
        Joonsoo Kim <>
        Sebastian Andrzej Siewior <>,
        Thomas Gleixner <>,
        Mel Gorman <>,
        Jesper Dangaard Brouer <>,
        Jann Horn <>
Subject: Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations
 __free_slab() invocations out of IRQ context

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.  That chain ending with cpu_hotplug_lock makes slub_cpu_dead()
> > taking slab_mutex a non-starter for cpu hotplug as well.  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 "existing
> 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 with 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 ;-)


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