On Wed, Dec 13, 2023 at 09:27:09AM -0500, Joel Fernandes wrote: > On Tue, Dec 12, 2023 at 12:48 PM Neeraj Upadhyay (AMD) > <neeraj.iitr10@xxxxxxxxx> wrote: > > > > From: Frederic Weisbecker <frederic@xxxxxxxxxx> > > > > If an SRCU barrier is queued while callbacks are running and a new > > callbacks invocator for the same sdp were to run concurrently, the > > RCU barrier might execute too early. As this requirement is non-obvious, > > make sure to keep a record. > > > > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx> > > Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@xxxxxxxxx> > > --- > > kernel/rcu/srcutree.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 2bfc8ed1eed2..0351a4e83529 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -1715,6 +1715,11 @@ static void srcu_invoke_callbacks(struct work_struct *work) > > WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL)); > > rcu_segcblist_advance(&sdp->srcu_cblist, > > rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq)); > > + /* > > + * Although this function is theoretically re-entrant, concurrent > > + * callbacks invocation is disallowed to avoid executing an SRCU barrier > > + * too early. > > + */ > > Side comment: > I guess even without the barrier reasoning, it is best not to allow > concurrent CB execution anyway since it diverges from the behavior of > straight RCU :) Good point! But please do not forget item 12 on the list in checklist.rst. ;-) (Which I just updated to include the other call_rcu*() functions.) Thanx, Paul
