Re: [PATCH] PM: wakeup: publish events_check_enabled with release semantics

[Rafael J. Wysocki (Intel)]

On Tue, Sep 22, 2026 at 3:25 AM Jaidev Shastri via B4 Relay
<devnull+jaidevshastri.vt.edu@xxxxxxxxxx> wrote:
>
> From: Jaidev Shastri <jaidevshastri@xxxxxx>
>
> pm_save_wakeup_count() stores saved_count and then events_check_enabled
> under events_lock. wakeup_source_report_event() reads
> events_check_enabled without the lock and counts the event.
>
> Store the flag with smp_store_release() and read it with
> smp_load_acquire(), so that the stores a reader may rely on after
> observing the flag are stated by the code.

And how exactly does this help?

> Found with MBCheck, a static herd7-based memory consistency checker.
>
> Signed-off-by: Jaidev Shastri <jaidevshastri@xxxxxx>
> ---
>  drivers/base/power/wakeup.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index 80b497de2..afc9fafaf 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -578,8 +578,11 @@ static void wakeup_source_activate(struct wakeup_source *ws)
>  static void wakeup_source_report_event(struct wakeup_source *ws, bool hard)
>  {
>         ws->event_count++;
> -       /* This is racy, but the counter is approximate anyway. */
> -       if (events_check_enabled)
> +       /*
> +        * This is racy, but the counter is approximate anyway. The acquire
> +        * pairs with the release in pm_save_wakeup_count().
> +        */
> +       if (smp_load_acquire(&events_check_enabled))
>                 ws->wakeup_count++;
>
>         if (!ws->active)
> @@ -1003,7 +1006,8 @@ bool pm_save_wakeup_count(unsigned int count)
>         split_counters(&cnt, &inpr);
>         if (cnt == count && inpr == 0) {
>                 saved_count = count;
> -               events_check_enabled = true;
> +               /* Pairs with the smp_load_acquire() in wakeup_source_report_event(). */
> +               smp_store_release(&events_check_enabled, true);
>         }
>         raw_spin_unlock_irqrestore(&events_lock, flags);
>         return events_check_enabled;
>
> ---
> base-commit: 93f51579e7df248780214094418f205253383cc5
> change-id: 20260921-mb-pm-wakeup-6bc4f1592414
>
> Best regards,
> --
> Jaidev Shastri <jaidevshastri@xxxxxx>
>
>