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David Hildenbrand
381eab4a6e
There seem to be some problems as result of30467e0b3b("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 after30467e0b3b. 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]>