linux-kernel - Re: [PATCH v3] PM / wakeup: use seq

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Message-ID: <20180429143002.GC13475@amd>
Date:   Sun, 29 Apr 2018 16:30:02 +0200
From:   Pavel Machek <pavel@....cz>
To:     Ganesh Mahendran <opensource.ganesh@...il.com>
Cc:     rjw@...ysocki.net, len.brown@...el.com, rafael@...nel.org,
        gregkh@...uxfoundation.org, geert@...ux-m68k.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PM / wakeup: use seq_open() to show wakeup stats

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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