linux-kernel - Re: [PATCH 2/8] PM / domains: Protect reading loop over list of domains

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Message-ID: <20170612131000.GA22241@kozik-book>
Date:   Mon, 12 Jun 2017 15:10:00 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>, Pavel Machek <pavel@....cz>,
        Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/8] PM / domains: Protect reading loop over list of
 domains

On Mon, Jun 12, 2017 at 02:57:21PM +0200, Ulf Hansson wrote:
> On 9 June 2017 at 18:16, Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > On Fri, Jun 09, 2017 at 06:08:47PM +0200, Krzysztof Kozlowski wrote:
> >> The pm_genpd_present() iterates over list of domains so grabbing a
> >> gpd_list_lock mutex is necessary before calling it.  Otherwise we could
> >> end up in iterating over and modifying the list at the same time.
> >>
> >> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> >> ---
> >>  drivers/base/power/domain.c | 7 ++++++-
> >>  1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> >> index 2e8d0f423507..2a6935dc0164 100644
> >> --- a/drivers/base/power/domain.c
> >> +++ b/drivers/base/power/domain.c
> >> @@ -1099,8 +1099,13 @@ static void genpd_syscore_switch(struct device *dev, bool suspend)
> >>       struct generic_pm_domain *genpd;
> >>
> >>       genpd = dev_to_genpd(dev);
> 
> Actually there may be potential problem here as we may end up trying
> to use the container_of() call for a PM domain, not being a genpd but
> something else.
> 
> >> -     if (!pm_genpd_present(genpd))
> >> +
> >> +     mutex_lock(&gpd_list_lock);
> >> +     if (!pm_genpd_present(genpd)) {
> >> +             mutex_unlock(&gpd_list_lock);
> >>               return;
> >> +     }
> >> +     mutex_unlock(&gpd_list_lock);
> 
> Perhaps convert the hole thing above to call genpd_lookup_dev() instead?

Indeed, that would solve both problems. Thanks, I'll fix this.

Best regards,
Krzysztof