On Mon, Dec 03, 2018 at 08:40:48AM -0800, Bart Van Assche wrote: > > I think we can do this with a free bitmap and an array of 2 pending > > bitmaps and an index. Add newly freed entries to the pending bitmap > > indicated by the current index, when complete flip the index -- such > > that further new bits go to the other pending bitmap -- and call_rcu(). > > > > Then, on the call_rcu() callback, ie. after a GP has happened, OR our > > pending bitmap into the free bitmap, and when the other pending bitmap > > isn't empty, flip the index again and start it all again. > > > > This ensures there is at least one full GP between setting a bit and it > > landing in the free mask. > > Hi Peter, > > How about the following alternative which requires only two bitmaps instead > of three: > - Maintain two bitmaps, one for the free entries and one for the entries > that are being freed. > - Protect all accesses to both bitmaps with the graph lock. > - zap_class() sets a bit in the "being freed" bitmap for the entries that > should be freed after a GP. > - Instead of making free_zapped_classes() wait for a grace period by calling > synchronize_sched(), use call_rcu() and do the freeing work from inside the > RCU callback. > - From inside the RCU callback, set a bit in the "free" bitmap for all entries > that have a bit set in the "being freed" bitmap and clears the "being freed" > bitmap. >
What happens when another unreg happens while the rcu_call thing is still pending?