On 1/14/26 09:52, Gregory Price wrote:
Add a memory notifier to prevent external operations from changing the
online/offline state of memory blocks managed by dax_kmem. This ensures
state changes only occur through the driver's hotplug sysfs interface,
providing consistent state tracking and preventing races with auto-online
policies or direct memory block sysfs manipulation.
The notifier uses a transition protocol with memory barriers:
- Before initiating a state change, set target_state then in_transition
- Use a barrier to ensure target_state is visible before in_transition
- The notifier checks in_transition, then uses barrier before reading
target_state to ensure proper ordering on weakly-ordered architectures
The notifier callback:
- Returns NOTIFY_DONE for non-overlapping memory (not our concern)
- Returns NOTIFY_BAD if in_transition is false (block external ops)
- Validates the memory event matches target_state (MEM_GOING_ONLINE
for online operations, MEM_GOING_OFFLINE for offline/unplug)
- Returns NOTIFY_OK only for driver-initiated operations with matching
target_state
This prevents scenarios where:
- Auto-online policies re-online memory the driver is trying to offline
Is this still a problem when using offline_and_remove_memory() ?
- Users manually change memory state via /sys/devices/system/memory/
I don't see why we would want to care about that :)
- Other kernel subsystems interfere with driver-managed memory state
What do you have in mind?
Not sure if this functionality here is really needed when the driver
does add+online and offline+remove in a single operation. So please
elaborate :)
--
Cheers
David
