linux-kernel - Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code

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Date:	Mon, 22 Jun 2015 09:30:20 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Geert Uytterhoeven <geert+renesas@...der.be>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Magnus Damm <damm@...nsource.se>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] PM / Domains: Avoid infinite loops in attach/detach code

On Thu, Jun 18, 2015 at 12:22 PM, Geert Uytterhoeven
<geert+renesas@...der.be> wrote:
> If pm_genpd_{add,remove}_device() keeps on failing with -EAGAIN, we end
> up with an infinite loop in genpd_dev_pm_{at,de}tach().
>
> This may happen due to a genpd.prepared_count imbalance.  This is a bug
> elsewhere, but it will result in a system lock up, possibly during
> reboot of an otherwise functioning system.
>
> To avoid this, put a limit on the maximum number of loop iterations,
> including a simple back-off mechanism.  If the limit is reached, the
> operation will just fail.  An error message is already printed.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
>  drivers/base/power/domain.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index cdd547bd67df8218..aa06f60b98b8af35 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c

> @@ -2218,10 +2226,13 @@ int genpd_dev_pm_attach(struct device *dev)
>
>         dev_dbg(dev, "adding to PM domain %s\n", pd->name);
>
> -       while (1) {
> +       for (i = 0; i < GENPD_RETRIES; i++) {

Sorry, there's a declaration of "i" missing.

>                 ret = pm_genpd_add_device(pd, dev);
>                 if (ret != -EAGAIN)
>                         break;
> +
> +               if (i > GENPD_RETRIES / 2)
> +                       udelay(GENPD_DELAY_US);
>                 cond_resched();
>         }
>
> --
> 1.9.1

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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