On 4/13/26 21:38, Gregory Price wrote: > On Mon, Apr 13, 2026 at 05:47:01PM +0200, David Hildenbrand (Arm) wrote: >> >> So, really only user space can try offlining the memory after requested >> onlining succeeded. >> >> I don't think any udev rules do that? The usually only request to >> online, which should be fine. >> > > In the offline case the block will cease to exist after offlin/remove > returns, so what should happen is the race on offline just fails and > the stale object cleans itself up on the way out after failure. > > Userland temporarily sees a stale memory block but can't do anything > with it because sync'd on hotplug lock.
Exactly. > >> So if a user does that manually, good for him. We just have to make sure >> that stuff keeps working as expected. >> > > Yeah the only catch is if a user does something dumb like > > cat block/state -> online_movable > echo offline > block/state > echo online > block/state > > But like... don't do that :] Yes :) > > Udev won't ever offline-online-race like this, so it's not a real issue. > >> Or am I missing a case? >> > > So yeah, I'm fairly confident this just works. > >> >> I'll note that offline_and_remove_memory() can take a long time/forever >> to succeed. User space can abort it by sending a critical signal. >> >> For example, if you do >> >> $ echo "unplugged" > magic_device_file >> >> And it hangs, user space can kill the "echo" command, sending a fatal >> signal and making offline_and_remove_memory() fail. >> >> The question is, if you want to do your best to revert the other offline >> operations and try re-adding/onlining what you already offlined. >> >> offline_and_remove_memory() handles that much nicer internally, as it >> tries to revert offlining, and only removes once everything was offlined. >> >> I think I raised it previously, but you could add a >> offline_and_remove_memory_ranges() that consumes multiple ranges, and >> would do this for you under a single lock_device_hotplug(). >> > > I don't think this is a very large lift, just a slightly larger hotplug > locking scope. But then - the per-range thing in this set should just > work, so let me know if it's worth the extra churn. Well, you can rather cleanly undo the operation if any offlining fails. If that's not a requirement, then no need to change it! -- Cheers, David
