mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock

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 a),
followed by b), exposing a possible deadlock.

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. This will
   be addressed in the following patches.

Now that we hold the device_hotplug_lock when
- adding memory (e.g. via add_memory()/add_memory_resource())
- removing memory (e.g. via remove_memory())
- device_online()/device_offline()

We can move mem_hotplug_lock usage back into
online_pages()/offline_pages().

Why is mem_hotplug_lock still needed? Essentially to make
get_online_mems()/put_online_mems() be very fast (relying on
device_hotplug_lock would be very slow), and to serialize against
addition of memory that does not create memory block devices (hmm).

[1] http://driverdev.linuxdriverproject.org/pipermail/ driverdev-devel/
    2015-February/065324.html

This patch is partly based on a patch by Vitaly Kuznetsov.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Pavel Tatashin <[email protected]>
Reviewed-by: Rashmica Gupta <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "K. Y. Srinivasan" <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Rashmica Gupta <[email protected]>
Cc: Michael Neuling <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: YASUAKI ISHIMATSU <[email protected]>
Cc: Mathieu Malaterre <[email protected]>
Cc: John Allen <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Nathan Fontenot <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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