There seem to be some problems as result of 30467e0b3b ("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 30467e0b3b. 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]>
381eab4a6e