linux-kernel - Re: [PATCH v1] drivers/acpi/scan.c: Fixup "acquire device_hotplug_lock in acpi_scan

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Message-ID: <d3cc595d-7e6f-ef6f-044c-b20bd1de3fb0@redhat.com>
Date:   Wed, 31 Jul 2019 15:02:49 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-acpi@...r.kernel.org,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v1] drivers/acpi/scan.c: Fixup "acquire
 device_hotplug_lock in acpi_scan_init()"

On 31.07.19 14:53, Michal Hocko wrote:
> On Wed 31-07-19 14:32:01, David Hildenbrand wrote:
>> Let's document why we take the lock here. If we're going to overhaul
>> memory hotplug locking, we'll have to touch many places - this comment
>> will help to clairfy why it was added here.
> 
> And how exactly is "lock for consistency" comment going to help the poor
> soul touching that code? How do people know that it is safe to remove it?
> I am not going to repeat my arguments how/why I hate "locking for
> consistency" (or fun or whatever but a real synchronization reasons)
> but if you want to help then just explicitly state what should done to
> remove this lock.
> 

I know that you have a different opinion here. To remove the lock,
add_memory() locking has to be changed *completely* to the point where
we can drop the lock from the documentation of the function (*whoever
knows what we have to exactly change* - and I don't have time to do that
*right now*).

-- 

Thanks,

David / dhildenb