On Thu, Mar 28, 2024 at 02:28:40PM +0900, Damien Le Moal wrote: > That was my thinking initially as well, which is why I did not have the > grace period. However, getting a reference on a plug is a not done under > disk->zone_wplugs_lock and is thus racy, albeit with a super tiny time > window: the hash table lookup may "see" a plug that has already been > removed and has a refcount dropped to 0 already. The use of > atomic_inc_not_zero() prevents us from trying to keep using that stale > plug, but we *are* referencing it. So without the grace period, I think > there is a risk (again, super tiny window) that we start reusing the > plug, or kfree it while atomic_inc_not_zero() is executing... > I am overthinking this ? Well. All the lookups fail (or should fail) when BLK_ZONE_WPLUG_UNHASHED is set, probably even before even trying to grab a reference. So all the lookups for a zone that is beeing torn down will fail. Now once the actual final reference is dropped, we'll now need to clear BLK_ZONE_WPLUG_UNHASHED and lookup can happe again. We'd have a race window there, but I guess we can plug it by checking for the right zone number? If we it while it already got reduce that'll still fail the lookup.
