[PATCH v3 3/3] rcu: Use _full() API to debug synchronize_rcu()

Uladzislau Rezki (Sony)
2025-02-25T11:00:26Z

Switch for using of get_state_synchronize_rcu_full() and
poll_state_synchronize_rcu_full() pair for debug a normal
synchronize_rcu() call.

Just using "not" full APIs to identify if a grace period
is passed or not might lead to a false kernel splat.

Link: https://lore.kernel.org/lkml/Z5ikQeVmVdsWQrdD@pc636/T/
Fixes: 988f569ae041 ("rcu: Reduce synchronize_rcu() latency")
Reported-by: cheung wall <zzqq0103.hey@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
include/linux/rcupdate_wait.h | 3 +++
kernel/rcu/tree.c | 8 +++-----
2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index f9bed3d3f78d..4c92d4291cce 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -16,6 +16,9 @@
struct rcu_synchronize {
struct rcu_head head;
struct completion completion;
+
+ /* This is for debugging. */
+ struct rcu_gp_oldstate oldstate;
};
void wakeme_after_rcu(struct rcu_head *head);

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8625f616c65a..48384fa2eaeb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1632,12 +1632,10 @@ static void rcu_sr_normal_complete(struct llist_node *node)
{
struct rcu_synchronize *rs = container_of(
(struct rcu_head *) node, struct rcu_synchronize, head);
- unsigned long oldstate = (unsigned long) rs->head.func;

WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) &&
- !poll_state_synchronize_rcu(oldstate),
- "A full grace period is not passed yet: %lu",
- rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
+ !poll_state_synchronize_rcu_full(&rs->oldstate),
+ "A full grace period is not passed yet!\n");

/* Finally. */
complete(&rs->completion);
@@ -3247,7 +3245,7 @@ static void synchronize_rcu_normal(void)
* snapshot before adding a request.
*/
if (IS_ENABLED(CONFIG_PROVE_RCU))
- rs.head.func = (void *) get_state_synchronize_rcu();
+ get_state_synchronize_rcu_full(&rs.oldstate);

rcu_sr_normal_add_req(&rs);

--
2.39.5