On Fri, Feb 06, 2026 at 12:30:56AM +0800, Lance Yang wrote: > On 2026/2/5 23:41, Dave Hansen wrote: > > Yeah, but one aim of RCU is ensuring that readers see valid data but not > > necessarily the most up to date data. > > > > Are there cases where ongoing concurrent lockless page-table walks need > > to see the writes and they can't tolerate seeing valid but slightly > > stale data? > > The issue is we're about to free the page table (e.g. > pmdp_collapse_flush()). > > We have to ensure no walker is still doing a lockless page-table walk > when the page directories are freed, otherwise we get use-after-free.
But can't we RCU-free the page table? Why do we need to wait for the RCU readers to finish?
