linux-kernel - Re: [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug

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Message-ID: <20190926073816.GC20255@dhcp22.suse.cz>
Date:   Thu, 26 Sep 2019 09:38:16 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Qian Cai <cai@....pw>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug_lock

On Thu 26-09-19 09:26:13, David Hildenbrand wrote:
[...]
> I'd like to hear what Michal thinks. If we do want the cpu hotplug lock,
> we can at least restrict it to the call paths (e.g., online_pages())
> where the lock is really needed and document that.

Completely agreed. Conflating cpu and memory hotplug locks was a bad
decision. If there are places which need both they should better use
both lock explicitly.

Now, the reality might turn out more complicated due to locks nesting
but hiding the cpu lock into the mem hotplug is just not fixing that.
-- 
Michal Hocko
SUSE Labs