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SubjectRe: [PATCH RFCv2 3/6] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
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?


> The series looks good to me. Feel free to add my reviewed-by:
> Reviewed-by: Rashmica Gupta <>

Thanks, r-b only for this patch or all of the series?



David / dhildenb

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