On Thu, Jan 23, 2025 at 07:58:28PM +0100, Uladzislau Rezki (Sony) wrote:
> 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.
>
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
> include/linux/rcupdate_wait.h | 4 ++++
> kernel/rcu/tree.c | 8 +++-----
> 2 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
> index f9bed3d3f78d..a16fc2a9a7d7 100644
> --- a/include/linux/rcupdate_wait.h
> +++ b/include/linux/rcupdate_wait.h
> @@ -16,6 +16,10 @@
> struct rcu_synchronize {
> struct rcu_head head;
> struct completion completion;
> +#ifdef CONFIG_PROVE_RCU
> + /* This is for testing. */
> + struct rcu_gp_oldstate oldstate;
> +#endif
> };
> void wakeme_after_rcu(struct rcu_head *head);
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 2795d6b5109c..0ae90089ef09 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1612,12 +1612,10 @@ 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");
Looks good, but why not also continue printing out the required
grace-period sequence number? Yes, there would need to be helper
sprintf()-style functions to paper over the difference between Tiny RCU
and Tree RCU. ;-)
Thanx, Paul
> /* Finally. */
> complete(&rs->completion);
> @@ -3214,7 +3212,7 @@ 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
>
