[PATCH 18/19] srcutree: Don't transition atomic SRCU to big in srcu_gp_end()

[Paul E. McKenney]

From: Kunwu Chan <kunwu.chan@xxxxxxxxx>

Atomic SRCU must remain in the small size state. Warn if this
invariant is violated and avoid transitioning to big in that case.

[ paulmck: Folded "if" onto one line for 100-character limit. ]

Signed-off-by: Kunwu Chan <kunwu.chan@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
---
 kernel/rcu/srcutree.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 4e9a0b8ea344..6a05bd8a6f39 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1073,8 +1073,10 @@ static void srcu_gp_end(struct srcu_struct *ssp, bool is_atomic)
 		raw_spin_unlock_irq_rcu_node(sup);
 	}
 
-	/* Transition to big if needed. */
-	if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
+	/* Transition to big if needed, but never for atomic SRCU. */
+	if (ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC && ss_state != SRCU_SIZE_SMALL) {
+		WARN_ON_ONCE(1);
+	} else if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
 		if (ss_state == SRCU_SIZE_ALLOC)
 			init_srcu_struct_nodes(ssp, GFP_KERNEL);
 		else
-- 
2.40.1