linux-kernel - Re: [PATCH RFC v1] mm: is_mem_section

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Message-ID: <20200120074816.GG18451@dhcp22.suse.cz>
Date:   Mon, 20 Jan 2020 08:48:16 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Leonardo Bras <leonardo@...ux.ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Allison Randal <allison@...utok.net>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Anshuman Khandual <anshuman.khandual@....com>,
        lantianyu1986@...il.com,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH RFC v1] mm: is_mem_section_removable() overhaul

On Fri 17-01-20 08:57:51, Dan Williams wrote:
[...]
> Unless the user is willing to hold the device_hotplug_lock over the
> evaluation then the result is unreliable.

Do we want to hold the device_hotplug_lock from this user readable file
in the first place? My book says that this just waits to become a
problem.

Really, the interface is flawed and should have never been merged in the
first place. We cannot simply remove it altogether I am afraid so let's
at least remove the bogus code and pretend that the world is a better
place where everything is removable except the reality sucks...
-- 
Michal Hocko
SUSE Labs