Re: [PATCH v8 2/3] freezer: refactor pm_freezing into a function.

[Rafael J. Wysocki]

On Thu, Dec 1, 2022 at 12:08 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote:
>
> Add a way to let the drivers know if the processes are frozen.
>
> This is needed by drivers that are waiting for processes to end on their
> shutdown path.
>
> Convert pm_freezing into a function and export it, so it can be used by
> drivers that are either built-in or modules.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 83bfc7e793b5 ("ASoC: SOF: core: unregister clients and machine drivers in .shutdown")
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>

Why can't you export the original pm_freezing variable and why is this
fixing anything?

> ---
>  include/linux/freezer.h |  3 ++-
>  kernel/freezer.c        |  3 +--
>  kernel/power/process.c  | 24 ++++++++++++++++++++----
>  3 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
> index b303472255be..3413c869d68b 100644
> --- a/include/linux/freezer.h
> +++ b/include/linux/freezer.h
> @@ -13,7 +13,7 @@
>  #ifdef CONFIG_FREEZER
>  DECLARE_STATIC_KEY_FALSE(freezer_active);
>
> -extern bool pm_freezing;               /* PM freezing in effect */
> +bool pm_freezing(void);
>  extern bool pm_nosig_freezing;         /* PM nosig freezing in effect */
>
>  /*
> @@ -80,6 +80,7 @@ static inline int freeze_processes(void) { return -ENOSYS; }
>  static inline int freeze_kernel_threads(void) { return -ENOSYS; }
>  static inline void thaw_processes(void) {}
>  static inline void thaw_kernel_threads(void) {}
> +static inline bool pm_freezing(void) { return false; }
>
>  static inline bool try_to_freeze(void) { return false; }
>
> diff --git a/kernel/freezer.c b/kernel/freezer.c
> index 4fad0e6fca64..2d3530ebdb7e 100644
> --- a/kernel/freezer.c
> +++ b/kernel/freezer.c
> @@ -20,7 +20,6 @@ EXPORT_SYMBOL(freezer_active);
>   * indicate whether PM freezing is in effect, protected by
>   * system_transition_mutex
>   */
> -bool pm_freezing;
>  bool pm_nosig_freezing;
>
>  /* protects freezing and frozen transitions */
> @@ -46,7 +45,7 @@ bool freezing_slow_path(struct task_struct *p)
>         if (pm_nosig_freezing || cgroup_freezing(p))
>                 return true;
>
> -       if (pm_freezing && !(p->flags & PF_KTHREAD))
> +       if (pm_freezing() && !(p->flags & PF_KTHREAD))
>                 return true;
>
>         return false;
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index ddd9988327fe..8a4d0e2c8c20 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -108,6 +108,22 @@ static int try_to_freeze_tasks(bool user_only)
>         return todo ? -EBUSY : 0;
>  }
>
> +/*
> + * Indicate whether PM freezing is in effect, protected by
> + * system_transition_mutex.
> + */
> +static bool pm_freezing_internal;
> +
> +/**
> + * pm_freezing - indicate whether PM freezing is in effect.
> + *
> + */
> +bool pm_freezing(void)
> +{
> +       return pm_freezing_internal;
> +}
> +EXPORT_SYMBOL(pm_freezing);

Use EXPORT_SYMBOL_GPL() instead, please.

> +
>  /**
>   * freeze_processes - Signal user space processes to enter the refrigerator.
>   * The current thread will not be frozen.  The same process that calls
> @@ -126,12 +142,12 @@ int freeze_processes(void)
>         /* Make sure this task doesn't get frozen */
>         current->flags |= PF_SUSPEND_TASK;
>
> -       if (!pm_freezing)
> +       if (!pm_freezing())
>                 static_branch_inc(&freezer_active);
>
>         pm_wakeup_clear(0);
>         pr_info("Freezing user space processes ... ");
> -       pm_freezing = true;
> +       pm_freezing_internal = true;
>         error = try_to_freeze_tasks(true);
>         if (!error) {
>                 __usermodehelper_set_disable_depth(UMH_DISABLED);
> @@ -187,9 +203,9 @@ void thaw_processes(void)
>         struct task_struct *curr = current;
>
>         trace_suspend_resume(TPS("thaw_processes"), 0, true);
> -       if (pm_freezing)
> +       if (pm_freezing())
>                 static_branch_dec(&freezer_active);
> -       pm_freezing = false;
> +       pm_freezing_internal = false;
>         pm_nosig_freezing = false;
>
>         oom_killer_enable();
>
> --