Commit 614ddad1 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Tighten rcu_advance_cbs_nowake() checks 



Currently, rcu_advance_cbs_nowake() checks that a grace period is in
progress, however, that grace period could end just after the check.
This commit rechecks that a grace period is still in progress while
holding the rcu_node structure's lock.  The grace period cannot end while
the current CPU's rcu_node structure's ->lock is held, thus avoiding
false positives from the WARN_ON_ONCE().

As Daniel Vacek noted, it is not necessary for the rcu_node structure
to have a CPU that has not yet passed through its quiescent state.

Tested-by: default avatarGuillaume Morin <guillaume@morinfr.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 8c0abfd6

kernel/rcu/tree.c

+4 −3
Original line number Diff line number Diff line
@@ -1590,9 +1590,10 @@ static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp, 
						  struct rcu_data *rdp)

{

	rcu_lockdep_assert_cblist_protected(rdp);

	if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||

	    !raw_spin_trylock_rcu_node(rnp))

	if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))

		return;

	// The grace period cannot end while we hold the rcu_node lock.

	if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))

		WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));

	raw_spin_unlock_rcu_node(rnp);

}