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Re: [Xen-devel] [PATCH RFCv2 3/6] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
- To: Rashmica <rashmica.g@xxxxxxxxx>, linux-mm@xxxxxxxxx
- From: David Hildenbrand <david@xxxxxxxxxx>
- Date: Mon, 17 Sep 2018 09:32:27 +0200
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- Cc: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxx>, linux-doc@xxxxxxxxxxxxxxx, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Balbir Singh <bsingharora@xxxxxxxxx>, Heiko Carstens <heiko.carstens@xxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Michael Neuling <mikey@xxxxxxxxxxx>, Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>, linux-acpi@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, Len Brown <lenb@xxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Dan Williams <dan.j.williams@xxxxxxxxx>, YASUAKI ISHIMATSU <yasu.isimatu@xxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Oscar Salvador <osalvador@xxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Mathieu Malaterre <malat@xxxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Philippe Ombredanne <pombredanne@xxxxxxxx>, Martin Schwidefsky <schwidefsky@xxxxxxxxxx>, devel@xxxxxxxxxxxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, linuxppc-dev@xxxxxxxxxxxxxxxx
- Delivery-date: Mon, 17 Sep 2018 07:33:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
Am 03.09.18 um 02:36 schrieb Rashmica:
> Hi David,
>
>
> On 21/08/18 20:44, David Hildenbrand wrote:
>
>> There seem to be some problems as result of 30467e0b3be ("mm, hotplug:
>> fix concurrent memory hot-add deadlock"), which tried to fix a possible
>> lock inversion reported and discussed in [1] due to the two locks
>> a) device_lock()
>> b) mem_hotplug_lock
>>
>> While add_memory() first takes b), followed by a) during
>> bus_probe_device(), onlining of memory from user space first took b),
>> followed by a), exposing a possible deadlock.
>
> Do you mean "onlining of memory from user space first took a),
> followed by b)"?
Very right, thanks.
>
>> In [1], and it was decided to not make use of device_hotplug_lock, but
>> rather to enforce a locking order.
>>
>> The problems I spotted related to this:
>>
>> 1. Memory block device attributes: While .state first calls
>> mem_hotplug_begin() and the calls device_online() - which takes
>> device_lock() - .online does no longer call mem_hotplug_begin(), so
>> effectively calls online_pages() without mem_hotplug_lock.
>>
>> 2. device_online() should be called under device_hotplug_lock, however
>> onlining memory during add_memory() does not take care of that.
>>
>> In addition, I think there is also something wrong about the locking in
>>
>> 3. arch/powerpc/platforms/powernv/memtrace.c calls offline_pages()
>> without locks. This was introduced after 30467e0b3be. And skimming over
>> the code, I assume it could need some more care in regards to locking
>> (e.g. device_online() called without device_hotplug_lock - but I'll
>> not touch that for now).
>
> Can you mention that you fixed this in later patches?
Sure!
>
>
> The series looks good to me. Feel free to add my reviewed-by:
>
> Reviewed-by: Rashmica Gupta <rashmica.g@xxxxxxxxx>
>
Thanks, r-b only for this patch or all of the series?
--
Thanks,
David / dhildenb
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