On Wed, Dec 05, 2018 at 09:03:24AM +0100, David Hildenbrand wrote: >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 > Ah, Thanks :-) > >Anyhow > >Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > >-- > >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
