[FSDP] summon_full_params fix (#73314)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/73314
Needs to synchronize all_gather stream. Added test fails without this
fix
ghstack-source-id: 149800363
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D34430602
fbshipit-source-id: 4ce07e2d098a4f07ac640285db1d0ff64fd42232
(cherry picked from commit 24c756e7bba69017b9358bf824589b2aeb366b5e)
