linux-kernel - Re: [PATCH v5] PM / wakeup: show wakeup sources stats in sysfs

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Message-ID: <20190730064657.GA1213@kroah.com>
Date:   Tue, 30 Jul 2019 08:46:57 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tri Vo <trong@...roid.com>
Cc:     rjw@...ysocki.net, viresh.kumar@...aro.org, rafael@...nel.org,
        hridya@...gle.com, sspatil@...gle.com, kaleshsingh@...gle.com,
        ravisadineni@...omium.org, swboyd@...omium.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kernel-team@...roid.com, kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v5] PM / wakeup: show wakeup sources stats in sysfs

On Mon, Jul 29, 2019 at 07:43:09PM -0700, Tri Vo wrote:
> Userspace can use wakeup_sources debugfs node to plot history of suspend
> blocking wakeup sources over device's boot cycle. This information can
> then be used (1) for power-specific bug reporting and (2) towards
> attributing battery consumption to specific processes over a period of
> time.
> 
> However, debugfs doesn't have stable ABI. For this reason, create a
> 'struct device' to expose wakeup sources statistics in sysfs under
> /sys/class/wakeup/wakeup<ID>/*.

I agree with Rafael here, no need for the extra "wakeup" in the device
name as you are in the "wakeup" namespace already.

If you have an IDA-allocated name, there's no need for the extra
'wakeup' at all.

> +int wakeup_source_sysfs_add(struct device *parent, struct wakeup_source *ws)
> +{
> +	struct device *dev;
> +	int id;
> +
> +	id = ida_simple_get(&wakeup_ida, 0, 0, GFP_KERNEL);
> +	if (id < 0)
> +		return id;

No lock needed for this ida?  Are you sure?

> +	ws->id = id;
> +
> +	dev = device_create_with_groups(wakeup_class, parent, MKDEV(0, 0), ws,
> +					wakeup_source_groups, "wakeup%d",
> +					ws->id);
> +	if (IS_ERR(dev)) {
> +		ida_simple_remove(&wakeup_ida, ws->id);
> +		return PTR_ERR(dev);
> +	}
> +
> +	ws->dev = dev;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(wakeup_source_sysfs_add);
> +
> +/**
> + * wakeup_source_sysfs_remove - Remove wakeup_source attributes from sysfs.
> + * @ws: Wakeup source to be removed from sysfs.
> + */
> +void wakeup_source_sysfs_remove(struct wakeup_source *ws)
> +{
> +	device_unregister(ws->dev);
> +	ida_simple_remove(&wakeup_ida, ws->id);

Again, no lock, is that ok?  I think ida's can work without a lock, but
not always, sorry, I don't remember the rules anymore given the recent
changes in that code.

thanks,

greg k-h