The IPC namespace code frees ipc_namespace structures asynchronously, via a work queue item. This results in ipc_namespace structures being freed very slowly, and the allocation path getting false failures since the to-be-freed ipc_namespace structures have not been freed yet. Fix that by having the allocator wait when there are ipc_namespace structures pending to be freed. Also speed up the freeing of ipc_namespace structures. We had some discussions about this last year, and ended up trying out various "nicer" ideas that did not work, so I went back to the original, with Al Viro's suggestion for a helper function: https://lore.kernel.org/all/Yg8StKzTWh+7FLuA@xxxxxxxxxxxxxxxxxxxxx/ This series fixes both the false allocation failures, and the slow freeing of ipc_namespace structures.
