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

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Date:   Mon, 20 Jan 2020 10:20:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     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 20.01.20 10:14, David Hildenbrand wrote:
> On 20.01.20 08:48, Michal Hocko wrote:
>> 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.
> 
> It was the "big hammer" solution for this RFC.
> 
> I think we could do with a try_lock() on the device_lock() paired with a
> device->removed flag. The latter is helpful for properly catching zombie
> devices on the onlining/offlining path either way (and on my todo list).

We do have dev->p->dead which could come in handy.

-- 
Thanks,

David / dhildenb