linux-kernel - Re: [PATCH v1] OPP: Fix crashing when current OPP has unsupportable voltage

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Date:   Mon, 24 Jun 2019 13:18:23 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        Marc Dietrich <marvin24@....de>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] OPP: Fix crashing when current OPP has unsupportable
 voltage

24.06.2019 10:18, Viresh Kumar пишет:
> On 23-06-19, 20:50, Dmitry Osipenko wrote:
>> Fix NULL dereference caused by a typo in the code. In particular it
>> happens when CPU is running on a frequency which has unsupportable voltage
>> (by regulator) defined in the OPP table and a custom set_opp() callback is
>> being used. The problem was spotted during of testing of upcoming update
>> for the NVIDIA Tegra CPUFreq driver.
>>
>> Cc: stable <stable@...r.kernel.org>
>> Fixes: 7e535993fa4f ("OPP: Separate out custom OPP handler specific code")
>> Reported-by: Marc Dietrich <marvin24@....de>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/opp/core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
>> index 9fda9a0ec016..89ec6aa220cf 100644
>> --- a/drivers/opp/core.c
>> +++ b/drivers/opp/core.c
>> @@ -685,7 +685,7 @@ static int _set_opp_custom(const struct opp_table *opp_table,
>>  
>>  	data->old_opp.rate = old_freq;
>>  	size = sizeof(*old_supply) * opp_table->regulator_count;
>> -	if (IS_ERR(old_supply))
>> +	if (!old_supply)
>>  		memset(data->old_opp.supplies, 0, size);
>>  	else
>>  		memcpy(data->old_opp.supplies, old_supply, size);
> 
> While the change is fine, the commit log isn't. It isn't about
> unsupportable voltage but frequency. The frequency the CPU is
> currently running at, is not present in the OPP table and so there is
> no corresponding OPP, hence no voltage supplies.

Ah, indeed! Looks like the reason for old OPP not being found was caused
by the appropriate OPP being disabled because of unsupportable voltage.
The offending higher "unsupportable" CPU freq was left after bootloader.

> I have applied this patch with following change log:
> 
> commit 560d1bcad715c215e7ffe5d7cffe045974b623d0 (HEAD -> opp/linux-next)
> Author: Dmitry Osipenko <digetx@...il.com>
> Date:   Sun Jun 23 20:50:53 2019 +0300
> 
>     opp: Don't use IS_ERR on invalid supplies
>     
>     _set_opp_custom() receives a set of OPP supplies as its arguments and
>     the caller of it passes NULL when the supplies are not valid. But
>     _set_opp_custom(), by mistake, checks for error by performing
>     IS_ERR(old_supply) on it which will always evaluate to false.
>     
>     The problem was spotted during of testing of upcoming update for the
>     NVIDIA Tegra CPUFreq driver.
>     
>     Cc: stable <stable@...r.kernel.org>
>     Fixes: 7e535993fa4f ("OPP: Separate out custom OPP handler specific code")
>     Reported-by: Marc Dietrich <marvin24@....de>
>     Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>     [ Viresh: Massaged changelog ]
>     Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/opp/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thank you very much!