[PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

[PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

[Ganesh Mahendran]

single_open() interface requires that the whole output must
fit into a single buffer. This will lead to timeout when
system memory is not in a good situation.

This patch use seq_open() to show wakeup stats. This method
need only one page, so timeout will not be observed.

Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
----
v3: simplify wakeup_sources_stats_seq_start
v2: use srcu_read_lock instead of rcu_read_lock
---
 drivers/base/power/wakeup.c | 75 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 59 insertions(+), 16 deletions(-)

diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
index ea01621..5872705 100644
--- a/drivers/base/power/wakeup.c
+++ b/drivers/base/power/wakeup.c
@@ -1029,32 +1029,75 @@ static int print_wakeup_source_stats(struct seq_file *m,
 	return 0;
 }
 
-/**
- * wakeup_sources_stats_show - Print wakeup sources statistics information.
- * @m: seq_file to print the statistics into.
- */
-static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
+static void *wakeup_sources_stats_seq_start(struct seq_file *m,
+					loff_t *pos)
 {
 	struct wakeup_source *ws;
-	int srcuidx;
+	loff_t n = *pos;
+	int *srcuidx = m->private;
 
-	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");
+	if (n == 0) {
+		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");
+	}
 
-	srcuidx = srcu_read_lock(&wakeup_srcu);
-	list_for_each_entry_rcu(ws, &wakeup_sources, entry)
-		print_wakeup_source_stats(m, ws);
-	srcu_read_unlock(&wakeup_srcu, srcuidx);
+	*srcuidx = srcu_read_lock(&wakeup_srcu);
+	list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
+		if (n-- <= 0)
+			return ws;
+	}
+
+	return NULL;
+}
+
+static void *wakeup_sources_stats_seq_next(struct seq_file *m,
+					void *v, loff_t *pos)
+{
+	struct wakeup_source *ws = v;
+	struct wakeup_source *next_ws = NULL;
+
+	++(*pos);
 
-	print_wakeup_source_stats(m, &deleted_ws);
+	list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
+		next_ws = ws;
+		break;
+	}
+
+	return next_ws;
+}
+
+static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
+{
+	int *srcuidx = m->private;
+
+	srcu_read_unlock(&wakeup_srcu, *srcuidx);
+}
+
+/**
+ * wakeup_sources_stats_seq_show - Print wakeup sources statistics information.
+ * @m: seq_file to print the statistics into.
+ * @v: wakeup_source of each iteration
+ */
+static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
+{
+	struct wakeup_source *ws = v;
+
+	print_wakeup_source_stats(m, ws);
 
 	return 0;
 }
 
+static const struct seq_operations wakeup_sources_stats_seq_ops = {
+	.start = wakeup_sources_stats_seq_start,
+	.next  = wakeup_sources_stats_seq_next,
+	.stop  = wakeup_sources_stats_seq_stop,
+	.show  = wakeup_sources_stats_seq_show,
+};
+
 static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
 {
-	return single_open(file, wakeup_sources_stats_show, NULL);
+	return seq_open_private(file, &wakeup_sources_stats_seq_ops, sizeof(int));
 }
 
 static const struct file_operations wakeup_sources_stats_fops = {
@@ -1062,7 +1105,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
 	.open = wakeup_sources_stats_open,
 	.read = seq_read,
 	.llseek = seq_lseek,
-	.release = single_release,
+	.release = seq_release_private,
 };
 
 static int __init wakeup_sources_debugfs_init(void)
-- 
1.9.1

Re: [PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

[Pavel Machek]

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On Wed 2018-04-25 18:59:31, Ganesh Mahendran wrote:
> single_open() interface requires that the whole output must
> fit into a single buffer. This will lead to timeout when
> system memory is not in a good situation.
> 
> This patch use seq_open() to show wakeup stats. This method
> need only one page, so timeout will not be observed.

Sounds like magic.

> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
> +					loff_t *pos)
>  {
...
> -	srcuidx = srcu_read_lock(&wakeup_srcu);
> -	list_for_each_entry_rcu(ws, &wakeup_sources, entry)
> -		print_wakeup_source_stats(m, ws);
> -	srcu_read_unlock(&wakeup_srcu, srcuidx);
> +	*srcuidx = srcu_read_lock(&wakeup_srcu);
> +	list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
> +		if (n-- <= 0)
> +			return ws;
> +	}
> +
> +	return NULL;
> +}
...
> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
> +{
> +	int *srcuidx = m->private;
> +
> +	srcu_read_unlock(&wakeup_srcu, *srcuidx);
> +}

But you are holding srcu_lock over return to userspace, and somehow I
don't think that's permitted?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: [PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

[Ganesh Mahendran]

Hi, Pavel

Thanks for your review.

2018-04-29 22:30 GMT+08:00 Pavel Machek <pavel@ucw.cz>:
> On Wed 2018-04-25 18:59:31, Ganesh Mahendran wrote:
>> single_open() interface requires that the whole output must
>> fit into a single buffer. This will lead to timeout when
>> system memory is not in a good situation.
>>
>> This patch use seq_open() to show wakeup stats. This method
>> need only one page, so timeout will not be observed.
>
> Sounds like magic.

I did not explain clearly here.

If we use single_open() to open the file, a single buffer(physical
continious) will be allocated
to store the whole data of file /sys/kernel/debug/wakeup_sources.
When memory situation is not good(fragments...), long time may be used
to allocate
such buffer which may cause android watchdog timeout.

>
>> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
>> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
>> +                                     loff_t *pos)
>>  {
> ...
>> -     srcuidx = srcu_read_lock(&wakeup_srcu);
>> -     list_for_each_entry_rcu(ws, &wakeup_sources, entry)
>> -             print_wakeup_source_stats(m, ws);
>> -     srcu_read_unlock(&wakeup_srcu, srcuidx);
>> +     *srcuidx = srcu_read_lock(&wakeup_srcu);
>> +     list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
>> +             if (n-- <= 0)
>> +                     return ws;
>> +     }
>> +
>> +     return NULL;
>> +}
> ...
>> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
>> +{
>> +     int *srcuidx = m->private;
>> +
>> +     srcu_read_unlock(&wakeup_srcu, *srcuidx);
>> +}
>
> But you are holding srcu_lock over return to userspace, and somehow I
> don't think that's permitted?

In seq_read(), the m->op->[start | stop] will be invoked as a pair.
So the srcu_lock will not be hold and return to userspace.

Thanks.

>                                                                         Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

[Rafael J. Wysocki]

On Wednesday, April 25, 2018 12:59:31 PM CEST Ganesh Mahendran wrote:
> single_open() interface requires that the whole output must
> fit into a single buffer. This will lead to timeout when
> system memory is not in a good situation.
> 
> This patch use seq_open() to show wakeup stats. This method
> need only one page, so timeout will not be observed.
> 
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
> ----
> v3: simplify wakeup_sources_stats_seq_start
> v2: use srcu_read_lock instead of rcu_read_lock
> ---
>  drivers/base/power/wakeup.c | 75 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 59 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index ea01621..5872705 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -1029,32 +1029,75 @@ static int print_wakeup_source_stats(struct seq_file *m,
>  	return 0;
>  }
>  
> -/**
> - * wakeup_sources_stats_show - Print wakeup sources statistics information.
> - * @m: seq_file to print the statistics into.
> - */
> -static int wakeup_sources_stats_show(struct seq_file *m, void *unused)
> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
> +					loff_t *pos)
>  {
>  	struct wakeup_source *ws;
> -	int srcuidx;
> +	loff_t n = *pos;
> +	int *srcuidx = m->private;
>  
> -	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");
> +	if (n == 0) {
> +		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");
> +	}
>  
> -	srcuidx = srcu_read_lock(&wakeup_srcu);
> -	list_for_each_entry_rcu(ws, &wakeup_sources, entry)
> -		print_wakeup_source_stats(m, ws);
> -	srcu_read_unlock(&wakeup_srcu, srcuidx);
> +	*srcuidx = srcu_read_lock(&wakeup_srcu);
> +	list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
> +		if (n-- <= 0)
> +			return ws;
> +	}
> +
> +	return NULL;
> +}
> +
> +static void *wakeup_sources_stats_seq_next(struct seq_file *m,
> +					void *v, loff_t *pos)
> +{
> +	struct wakeup_source *ws = v;
> +	struct wakeup_source *next_ws = NULL;
> +
> +	++(*pos);
>  
> -	print_wakeup_source_stats(m, &deleted_ws);
> +	list_for_each_entry_continue_rcu(ws, &wakeup_sources, entry) {
> +		next_ws = ws;
> +		break;
> +	}
> +
> +	return next_ws;
> +}
> +
> +static void wakeup_sources_stats_seq_stop(struct seq_file *m, void *v)
> +{
> +	int *srcuidx = m->private;
> +
> +	srcu_read_unlock(&wakeup_srcu, *srcuidx);
> +}
> +
> +/**
> + * wakeup_sources_stats_seq_show - Print wakeup sources statistics information.
> + * @m: seq_file to print the statistics into.
> + * @v: wakeup_source of each iteration
> + */
> +static int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
> +{
> +	struct wakeup_source *ws = v;
> +
> +	print_wakeup_source_stats(m, ws);
>  
>  	return 0;
>  }
>  
> +static const struct seq_operations wakeup_sources_stats_seq_ops = {
> +	.start = wakeup_sources_stats_seq_start,
> +	.next  = wakeup_sources_stats_seq_next,
> +	.stop  = wakeup_sources_stats_seq_stop,
> +	.show  = wakeup_sources_stats_seq_show,
> +};
> +
>  static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>  {
> -	return single_open(file, wakeup_sources_stats_show, NULL);
> +	return seq_open_private(file, &wakeup_sources_stats_seq_ops, sizeof(int));
>  }
>  
>  static const struct file_operations wakeup_sources_stats_fops = {
> @@ -1062,7 +1105,7 @@ static int wakeup_sources_stats_open(struct inode *inode, struct file *file)
>  	.open = wakeup_sources_stats_open,
>  	.read = seq_read,
>  	.llseek = seq_lseek,
> -	.release = single_release,
> +	.release = seq_release_private,
>  };
>  
>  static int __init wakeup_sources_debugfs_init(void)
> 

Applied, thanks!