Re: [PATCH v4 29/35] mm: slub: Move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context

[Mike Galbraith]

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 ;-)

	-Mike