On 6/24/26 16:57, Gregory Price wrote: > There is no atomic mechanism to offline and remove an entire > multi-block DAX kmem device. This is presently done in two steps: > 1. offline all > 2. remove all). > > This creates a race condition where another entity operates directly > on the memory blocks and can cause hot-unplug to fail / unbind to > deadlock. > > Add a new 'state' sysfs attribute that enables an atomic whole-device > hotplug operation across its entire memory region. > > daxX.Y/state mirrors the per-block memoryX/state ABI: > - [offline, online, online_kernel, online_movable] > - "unplugged" - is added specifically for dax0.0/state > > The valid writable states include: > - "unplugged": memory blocks are not present > - "online": memory is online, zone chosen by the kernel > - "online_kernel": memory is online in ZONE_NORMAL > - "online_movable": memory is online in ZONE_MOVABLE > > Valid transitions: > - unplugged -> online[_kernel|_movable] > - online[_kernel|_movable] -> unplugged > - offline -> unplugged > > A device can only be onlined from "unplugged", so it must be returned > there before being onlined into a different state. > > For backwards compatibility the memory blocks are always created at > probe - existing tools expect them to be present after kmem binds. > > "offline" is therefore a reportable state but is not writable: it only > arises from the legacy auto_online_blocks=offline policy. Onlining > such a device through this attribute requires unplugging it first in > an effort to get drivers creating DAX devices to set a default. > > Unplug is atomic across the whole device: dax_kmem_do_hotremove() > collects every added range and offlines/removes them in one operation. > Either the operation succeeds or is entirely rolled back. > > Unbind Note: > We used to call remove_memory() during unbind, which would fire a > BUG() if any of the memory blocks were online at that time. We lift > this into a WARN in the cleanup routine and don't attempt hotremove > if ->state is not DAX_KMEM_UNPLUGGED or MMOP_OFFLINE. > > An offline dax device memory is removed on unbind as before. > > If online at unbind, the resources are leaked (as before), but now > we prevent deadlock if a memory region is impossible to hotremove. > > Suggested-by: Hannes Reinecke <[email protected]> > Suggested-by: David Hildenbrand <[email protected]> > Signed-off-by: Gregory Price <[email protected]> > --- > Documentation/ABI/testing/sysfs-bus-dax | 26 +++ > drivers/base/memory.c | 9 +
Can we have this ... > drivers/dax/kmem.c | 224 ++++++++++++++++++++---- > include/linux/memory_hotplug.h | 1 + > ... and this as a separate patch, please? Nothing else jumped at me. -- Cheers, David
