On 05.12.18 03:34, Wei Yang wrote: > Locking Internal section exists in core-api documentation, which is more > suitable for this. > > This patch removes the duplication part here. > > Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> > --- > Documentation/admin-guide/mm/memory-hotplug.rst | 40 ------------------------- > 1 file changed, 40 deletions(-) > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index 5c4432c96c4b..241f4ce1e387 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -392,46 +392,6 @@ 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 > =========== > > I reported this yesterday to Jonathan and Mike https://lkml.org/lkml/2018/12/3/340 Anyhow Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> -- Thanks, David / dhildenb
