diff mbox series

[5.4,02/11] rcu: Tighten rcu_advance_cbs_nowake() checks

Message ID 20220127180258.442604866@linuxfoundation.org
State Superseded
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Jan. 27, 2022, 6:09 p.m. UTC 
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(-)
diff mbox series

Patch

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1358,10 +1358,11 @@  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);
 }