Merge branch 'akpm' (patches from Andrew)

Merge more updates from Andrew Morton:

 - the rest of MM

 - lib/bitmap updates

 - hfs updates

 - fatfs updates

 - various other misc things

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (94 commits)
  mm/gup.c: fix __get_user_pages_fast() comment
  mm: Fix warning in insert_pfn()
  memory-hotplug.rst: add some details about locking internals
  powerpc/powernv: hold device_hotplug_lock when calling memtrace_offline_pages()
  powerpc/powernv: hold device_hotplug_lock when calling device_online()
  mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
  mm/memory_hotplug: make add_memory() take the device_hotplug_lock
  mm/memory_hotplug: make remove_memory() take the device_hotplug_lock
  mm/memblock.c: warn if zero alignment was requested
  memblock: stop using implicit alignment to SMP_CACHE_BYTES
  docs/boot-time-mm: remove bootmem documentation
  mm: remove include/linux/bootmem.h
  memblock: replace BOOTMEM_ALLOC_* with MEMBLOCK variants
  mm: remove nobootmem
  memblock: rename __free_pages_bootmem to memblock_free_pages
  memblock: rename free_all_bootmem to memblock_free_all
  memblock: replace free_bootmem_late with memblock_free_late
  memblock: replace free_bootmem{_node} with memblock_free
  mm: nobootmem: remove bootmem allocation APIs
  memblock: replace alloc_bootmem with memblock_alloc
  ...

1 files changed, 41 insertions, 1 deletions

diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 25157aec5b31..5c4432c96c4b 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -5,7 +5,7 @@ Memory Hotplug
 ==============
 
 :Created:							Jul 28 2007
-:Updated: Add description of notifier of memory hotplug:	Oct 11 2007
+:Updated: Add some details about locking internals:		Aug 20 2018
 
 This document is about memory hotplug including how-to-use and current status.
 Because Memory Hotplug is still under development, contents of this text will
@@ -392,6 +392,46 @@ Need more implementation yet....
  - Notification completion of remove works by OS to firmware.
  - Guard from remove if not yet.
 
+
+Locking Internals
+=================
+
+When adding/removing memory that uses memory block devices (i.e. ordinary RAM),
+the device_hotplug_lock should be held to:
+
+- synchronize against online/offline requests (e.g. via sysfs). This way, memory
+  block devices can only be accessed (.online/.state attributes) by user
+  space once memory has been fully added. And when removing memory, we
+  know nobody is in critical sections.
+- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC)
+
+Especially, there is a possible lock inversion that is avoided using
+device_hotplug_lock when adding memory and user space tries to online that
+memory faster than expected:
+
+- device_online() will first take the device_lock(), followed by
+  mem_hotplug_lock
+- add_memory_resource() will first take the mem_hotplug_lock, followed by
+  the device_lock() (while creating the devices, during bus_add_device()).
+
+As the device is visible to user space before taking the device_lock(), this
+can result in a lock inversion.
+
+onlining/offlining of memory should be done via device_online()/
+device_offline() - to make sure it is properly synchronized to actions
+via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type)
+
+When adding/removing/onlining/offlining memory or adding/removing
+heterogeneous/device memory, we should always hold the mem_hotplug_lock in
+write mode to serialise memory hotplug (e.g. access to global/zone
+variables).
+
+In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read
+mode allows for a quite efficient get_online_mems/put_online_mems
+implementation, so code accessing memory can protect from that memory
+vanishing.
+
+
 Future Work
 ===========