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

From: Rafael J. Wysocki
Date: Fri Mar 02 2018 - 05:17:02 EST


On Fri, Mar 2, 2018 at 6:01 AM, Ganesh Mahendran
<opensource.ganesh@xxxxxxxxx> 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.

Did you actually see this problem with this particular file or is it
theoretical?

> 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@xxxxxxxxx>
> ---
> drivers/base/power/wakeup.c | 71 +++++++++++++++++++++++++++++++++++----------
> 1 file changed, 56 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/base/power/wakeup.c b/drivers/base/power/wakeup.c
> index ea01621..c64609a 100644
> --- a/drivers/base/power/wakeup.c
> +++ b/drivers/base/power/wakeup.c
> @@ -1029,32 +1029,73 @@ static int print_wakeup_source_stats(struct seq_file *m,
> return 0;
> }
>
> +static void *wakeup_sources_stats_seq_start(struct seq_file *m,
> + loff_t *pos)
> +{
> + struct wakeup_source *ws;
> + loff_t n = *pos;
> +
> + 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");
> + }
> +
> + rcu_read_lock();

The code running after this cannot sleep. Use
srcu_read_lock(&wakeup_srcu) instead.

> + list_for_each_entry_rcu(ws, &wakeup_sources, entry) {
> + if (n-- > 0)
> + continue;
> + goto out;
> + }
> + ws = NULL;
> +out:
> + return ws;
> +}
> +
> +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);
> +
> + 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)
> +{
> + rcu_read_unlock();
> +}
> +
> /**
> * 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 int wakeup_sources_stats_seq_show(struct seq_file *m, void *v)
> {
> - struct wakeup_source *ws;
> - int srcuidx;
> + struct wakeup_source *ws = v;
>
> - 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);
> -
> - print_wakeup_source_stats(m, &deleted_ws);
> + 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(file, &wakeup_sources_stats_seq_ops);
> }
>
> static const struct file_operations wakeup_sources_stats_fops = {
> @@ -1062,7 +1103,7 @@ 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,
> };
>
> static int __init wakeup_sources_debugfs_init(void)
> --
> 1.9.1
>