On Wed, Oct 23, 2024 at 02:58:07PM +0800, Alan Huang wrote: > On Oct 22, 2024, at 22:26, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > On Tue, Oct 22, 2024 at 12:13:12AM -0700, Christoph Hellwig wrote: > >> On Tue, Oct 22, 2024 at 09:10:18AM +0200, Peter Zijlstra wrote: > >>> Ah, well, the thing that got us here is that we (Andrii and me) wanted > >>> to use -1 as an 'invalid' value to indicate SRCU is not currently in > >>> use. > >>> > >>> So it all being int is really rather convenient :-) > >> > >> Then please document that use. Maybe even with a symolic name for > >> -1 that clearly describes these uses. > > > > Would this work? > > > > #define SRCU_INVALID_INDEX -1 > > Is there any similar guarantee of the return value of get_state_synchronize_rcu > or start_poll_synchronize_rcu, like invalid value? Yes, there is a get_completed_synchronize_rcu() function that returns a value that causes poll_state_synchronize_rcu() to always return true. There is also a get_completed_synchronize_rcu_full() function that returns a value that causes poll_state_synchronize_rcu_full() to always return true. There has been some discussion of another set of values that cause poll_state_synchronize_rcu() and poll_state_synchronize_rcu_full() to always return false, but there is not yet a use case for this. Easy to provide if required, but why further explode the RCU API unless it really is required? Thanx, Paul > > Whatever the name, maybe Peter and Andrii define this under #ifndef > > right now, and we get it into include/linux/srcu.h over time. > > > > Or is there a better way? Or name, for that matter. > > > > Thanx, Paul > > >
