On Tue, Feb 18, 2025 at 11:46:26AM +1000, Dave Airlie wrote: > > 1. How to avoid unnecessary calls to try_access(). > > > > This is why I made Boot0.read() take a &RevocableGuard<'_, Bar0> as argument. I > > think we can just call try_access() once and then propage the guard through the > > callchain, where necessary. > > Nope, you can't do that, RevocableGuard holds a lock and things > explode badly in lockdep if you do. Yes, try_access() marks the begin of an RCU read side critical section. Hence, sections holding the guard should be kept as short as possible. What I meant is that for a series of I/O operations we can still pass the guard to subsequent functions doing the actual I/O ops. More generally, I also thought about whether we should also provide an SRCU variant of Revocable and hence Devres. Maybe we even want to replace it with SRCU entirely to ensure that drivers can't stall the RCU grace period for too long by accident.
