From: Paul E. McKenney paulmck@kernel.org
commit 614ddad17f22a22e035e2ea37a04815f50362017 upstream.
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: Guillaume Morin guillaume@morinfr.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/rcu/tree.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
--- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1594,10 +1594,11 @@ static void __maybe_unused rcu_advance_c 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; - WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); + // 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); }