[PATCH v3 1/2] memory-hotplug.rst: remove locking details from admin-guide
From: David Hildenbrand <hidden>
Date: 2021-06-09 07:58:22
Also in:
linux-mm, lkml
Subsystem:
documentation, memory hot(un)plug, memory management - misc, the rest · Maintainers:
Jonathan Corbet, David Hildenbrand, Oscar Salvador, Andrew Morton, Linus Torvalds
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. Acked-by: Mike Rapoport <redacted> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <redacted> Cc: Mike Rapoport <rppt@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Anshuman Khandual <redacted> Cc: Muchun Song <redacted> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Stephen Rothwell <redacted> Cc: linux-doc@vger.kernel.org Signed-off-by: David Hildenbrand <redacted> --- .../admin-guide/mm/memory-hotplug.rst | 39 ------------------- 1 file changed, 39 deletions(-)
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index c6bae2d77160..a783cf7c8e4c 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/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 ===========
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2.31.1