The patch titled
Subject: memory-hotplug.rst: remove locking details from admin-guide
has been added to the -mm tree. Its filename is
memory-hotplugrst-remove-locking-details-from-admin-guide.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/memory-hotplugrst-remove-locking-details-from-admin-guide.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/memory-hotplugrst-remove-locking-details-from-admin-guide.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: memory-hotplug.rst: remove locking details from admin-guide
Patch series "memory-hotplug.rst: complete admin-guide overhaul", v3.
This patch (of 2):
We have the same content at Documentation/core-api/memory-hotplug.rst and
it doesn't fit into the admin-guide. The documentation was accidentially
duplicated when merging.
Link: https://lkml.kernel.org/r/20210707073205.3835-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20210707073205.3835-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/memory-hotplug.rst | 39 --------------
1 file changed, 39 deletions(-)
--- a/Documentation/admin-guide/mm/memory-hotplug.rst~memory-hotplugrst-remove-locking-details-from-admin-guide
+++ a/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -415,45 +415,6 @@ Need more implementation yet....
- 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
===========
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
memory-hotplugrst-remove-locking-details-from-admin-guide.patch
memory-hotplugrst-complete-admin-guide-overhaul.patch
