Re: PM / wakeirq: Convert to SRCU

[Paul E. McKenney]

On Sat, Jun 24, 2017 at 11:56:11AM +0200, Thomas Gleixner wrote:
> The wakeirq infrastructure uses RCU to protect the list of wakeirqs. That
> breaks the irq bus locking infrastructure, which allows sleeping functions
> to be called so interrupt controllers behind slow busses, e.g. i2c, can be
> handled.
> 
> The wakeirq functions hold rcu_read_lock and call into irq functions, which
> in case of interrupts using the irq bus locking will trigger a
> might_sleep() splat.
> 
> Convert the wakeirq infrastructure to Sleepable RCU and unbreak it.
> 
> Fixes: 4990d4fe327b ("PM / Wakeirq: Add automated device wake IRQ handling")
> Reported-by: Brian Norris <briannorris@xxxxxxxxxxxx>
> Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

Looks plausible.  One suggestion on initialization below, and a couple
of questions about uses of RCU that this patch does not convert to SRCU.

							Thanx, Paul

> ---
>  drivers/base/power/wakeup.c |   20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)
> 
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -60,6 +60,8 @@ static LIST_HEAD(wakeup_sources);
> 
>  static DECLARE_WAIT_QUEUE_HEAD(wakeup_count_wait_queue);
> 
> +static struct srcu_struct wakeup_srcu;

I suggest this to avoid the need for boot-time init_srcu_struct():

DEFINE_STATIC_SRCU(wakeup_srcu);

> +
>  static struct wakeup_source deleted_ws = {
>  	.name = "deleted",
>  	.lock =  __SPIN_LOCK_UNLOCKED(deleted_ws.lock),
> @@ -198,7 +200,7 @@ void wakeup_source_remove(struct wakeup_
>  	spin_lock_irqsave(&events_lock, flags);
>  	list_del_rcu(&ws->entry);
>  	spin_unlock_irqrestore(&events_lock, flags);
> -	synchronize_rcu();
> +	synchronize_srcu(&wakeup_srcu);
>  }
>  EXPORT_SYMBOL_GPL(wakeup_source_remove);

The uses of RCU in device_wakeup_arm_wake_irqs() and
device_wakeup_disarm_wake_irqs() are unrelated and thus do not
need to be converted?  Or am I looking at the wrong version of
the kernel?  (Looking at f65013d655ac ("Merge branch 'for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace")
in Linus's tree.)

If these two functions are making unrelated use of RCU and thus don't
need to be converted to SRCU, might be worth a comment somewhere.

> @@ -804,10 +806,10 @@ EXPORT_SYMBOL_GPL(pm_wakeup_dev_event);
>  void pm_print_active_wakeup_sources(void)
>  {
>  	struct wakeup_source *ws;
> -	int active = 0;
> +	int srcuidx, active = 0;
>  	struct wakeup_source *last_activity_ws = NULL;
> 
> -	rcu_read_lock();
> +	srcuidx = srcu_read_lock(&wakeup_srcu);
>  	list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
>  		if (ws->active) {
>  			pr_debug("active wakeup source: %s\n", ws->name);
> @@ -823,7 +825,7 @@ void pm_print_active_wakeup_sources(void
>  	if (!active && last_activity_ws)
>  		pr_debug("last active wakeup source: %s\n",
>  			last_activity_ws->name);
> -	rcu_read_unlock();
> +	srcu_read_unlock(&wakeup_srcu, srcuidx);
>  }
>  EXPORT_SYMBOL_GPL(pm_print_active_wakeup_sources);
> 
> @@ -950,8 +952,9 @@ void pm_wakep_autosleep_enabled(bool set
>  {
>  	struct wakeup_source *ws;
>  	ktime_t now = ktime_get();
> +	int srcuidx;
> 
> -	rcu_read_lock();
> +	srcuidx = srcu_read_lock(&wakeup_srcu);
>  	list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
>  		spin_lock_irq(&ws->lock);
>  		if (ws->autosleep_enabled != set) {
> @@ -965,7 +968,7 @@ void pm_wakep_autosleep_enabled(bool set
>  		}
>  		spin_unlock_irq(&ws->lock);
>  	}
> -	rcu_read_unlock();
> +	srcu_read_unlock(&wakeup_srcu, srcuidx);
>  }
>  #endif /* CONFIG_PM_AUTOSLEEP */

Same question for pm_wakep_autosleep_enabled().

> @@ -1026,15 +1029,16 @@ static int print_wakeup_source_stats(str
>  static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
>  {
>  	struct wakeup_source *ws;
> +	int srcuidx;
> 
>  	seq_puts(m, "name\t\tactive_count\tevent_count\twakeup_count\t"
>  		"expire_count\tactive_since\ttotal_time\tmax_time\t"
>  		"last_change\tprevent_suspend_time\n");
> 
> -	rcu_read_lock();
> +	srcuidx = srcu_read_lock(&wakeup_srcu);
>  	list_for_each_entry_rcu(ws, &wakeup_sources, entry)
>  		print_wakeup_source_stats(m, ws);
> -	rcu_read_unlock();
> +	srcu_read_unlock(&wakeup_srcu, srcuidx);
> 
>  	print_wakeup_source_stats(m, &deleted_ws);
> 
>