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

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Date:   Mon, 12 Jun 2017 14:57:21 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Krzysztof Kozlowski <krzk@...nel.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 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?

>
> Eh, I might be too fast as this is not executed on my platform.  The
> genpd_syscore_switch() seems to be called by clocksource_suspend() which
> is called by syscore ops. Should be safe but actually not tested.
>
> Someone with SH hardware is needed...
>
> Best regards,
> Krzysztof
>

Kind regards
Uffe