On Fri, Feb 21, 2025 at 01:16:00AM +0100, Marco Elver wrote: > On Thu, 20 Feb 2025 at 23:36, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > [...] > > Suppose that one function walks an RCU-protected list, calling some > > function from some other subsystem on each element. Suppose that each > > element has another RCU protected list. > > > > It would be good if the two subsystems could just choose their desired > > flavor of RCU reader, without having to know about each other. > > That's what I figured might be the case - thanks for clarifying. > > > > Another problem was that if we want to indicate that "RCU" read lock > > > is held, then we should just be able to write > > > "__must_hold_shared(RCU)", and it shouldn't matter if rcu_read_lock() > > > or rcu_read_lock_bh() was used. Previously each of them acquired their > > > own capability "RCU" and "RCU_BH" respectively. But rather, we're > > > dealing with one acquiring a superset of the other, and expressing > > > that is also what I attempted to solve. > > > Let me rethink this... > > > > Would it work to have just one sort of RCU reader, relying on a separate > > BH-disable capability for the additional semantics of rcu_read_lock_bh()? > > That's what I've tried with this patch (rcu_read_lock_bh() also > acquires "RCU", on top of "RCU_BH"). I need to add a re-entrancy test, > and make sure it doesn't complain about that. At a later stage we > might also want to add more general "BH" and "IRQ" capabilities to > denote they're disabled when held, but that'd overcomplicate the first > version of this series. Fair enough! Then would it work to just do "RCU" now, and ad the "BH" and "IRQ" when those capabilities are added? Thanx, Paul
