Re: [PATCH 1/2] PM: sleep: publish pm_transition with release semantics

[Rafael J. Wysocki (Intel)]

On Tue, Sep 22, 2026 at 3:24 AM Jaidev Shastri via B4 Relay
<devnull+jaidevshastri.vt.edu@xxxxxxxxxx> wrote:
>
> From: Jaidev Shastri <jaidevshastri@xxxxxx>
>
> Each dpm_*() phase function stores the current transition to
> pm_transition with a plain store before it schedules the asynchronous
> device callbacks. dev_pm_skip_resume() and pm_hibernate_is_recovering()
> read pm_transition.event from those callbacks, on other CPUs, with plain
> loads.

So how *exactly* is the race possible?

> Store the event with smp_store_release() and read it with
> smp_load_acquire().
>
> Found with MBCheck, a static herd7-based memory consistency checker.
>
> Signed-off-by: Jaidev Shastri <jaidevshastri@xxxxxx>
> ---
>  drivers/base/power/main.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index e130da428..bf4b4fd1b 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -78,7 +78,8 @@ static int async_error;
>   */
>  bool pm_hibernate_is_recovering(void)
>  {
> -       return pm_transition.event == PM_EVENT_RECOVER;
> +       /* Pairs with the smp_store_release() in the dpm_*() phase functions. */
> +       return smp_load_acquire(&pm_transition.event) == PM_EVENT_RECOVER;
>  }
>  EXPORT_SYMBOL_GPL(pm_hibernate_is_recovering);
>
> @@ -682,10 +683,13 @@ static void dpm_watchdog_clear(struct dpm_watchdog *wd)
>   */
>  bool dev_pm_skip_resume(struct device *dev)
>  {
> -       if (pm_transition.event == PM_EVENT_RESTORE)
> +       /* Pairs with the smp_store_release() in the dpm_*() phase functions. */
> +       int event = smp_load_acquire(&pm_transition.event);
> +
> +       if (event == PM_EVENT_RESTORE)
>                 return false;
>
> -       if (pm_transition.event == PM_EVENT_THAW)
> +       if (event == PM_EVENT_THAW)
>                 return dev_pm_skip_suspend(dev);
>
>         return !dev->power.must_resume;
> @@ -902,7 +906,8 @@ static void dpm_noirq_resume_devices(pm_message_t state)
>         trace_suspend_resume(TPS("dpm_resume_noirq"), state.event, true);
>
>         async_error = 0;
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>
>         mutex_lock(&dpm_list_mtx);
>
> @@ -1052,7 +1057,8 @@ void dpm_resume_early(pm_message_t state)
>         trace_suspend_resume(TPS("dpm_resume_early"), state.event, true);
>
>         async_error = 0;
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>
>         mutex_lock(&dpm_list_mtx);
>
> @@ -1230,7 +1236,8 @@ void dpm_resume(pm_message_t state)
>
>         trace_suspend_resume(TPS("dpm_resume"), state.event, true);
>
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>         async_error = 0;
>
>         mutex_lock(&dpm_list_mtx);
> @@ -1595,7 +1602,8 @@ static int dpm_noirq_suspend_devices(pm_message_t state)
>
>         trace_suspend_resume(TPS("dpm_suspend_noirq"), state.event, true);
>
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>         async_error = 0;
>
>         mutex_lock(&dpm_list_mtx);
> @@ -1798,7 +1806,8 @@ int dpm_suspend_late(pm_message_t state)
>
>         trace_suspend_resume(TPS("dpm_suspend_late"), state.event, true);
>
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>         async_error = 0;
>
>         wake_up_all_idle_cpus();
> @@ -2091,7 +2100,8 @@ int dpm_suspend(pm_message_t state)
>         devfreq_suspend();
>         cpufreq_suspend();
>
> -       pm_transition = state;
> +       /* Pairs with the smp_load_acquire() in dev_pm_skip_resume(). */
> +       smp_store_release(&pm_transition.event, state.event);
>         async_error = 0;
>
>         mutex_lock(&dpm_list_mtx);
>
> --
> 2.43.0
>
>