linux-kernel - Re: [RFC PATCH] regulator: Fix recursive mutex lockdep warning

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Message-ID: <55C30CD9.9090408@linaro.org>
Date:	Thu, 06 Aug 2015 08:29:29 +0100
From:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
CC:	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] regulator: Fix recursive mutex lockdep warning

Thanks Krzysztof

On 06/08/15 02:39, Krzysztof Kozlowski wrote:
>> --- a/drivers/regulator/core.c
>> >+++ b/drivers/regulator/core.c
>> >@@ -2919,7 +2919,7 @@ static int _regulator_get_voltage(struct regulator_dev *rdev)
>> >         } else if (rdev->desc->fixed_uV && (rdev->desc->n_voltages == 1)) {
>> >                 ret = rdev->desc->fixed_uV;
>> >         } else if (rdev->supply) {
>> >-               ret = regulator_get_voltage(rdev->supply);
>> >+               ret = _regulator_get_voltage(rdev->supply->rdev);
> Is the 'rdev' and 'rdev->supply' same regulators? If not then you are
> just hiding false warning by removing locks thus introducing real
> issue...
They are the not the same regulators, and hence they are not locking the 
same mutex, looks like this is a false positive warning from lockdep. I 
can't think of any use case which could result in ABBA type lockup too, 
so we can ignore this patch for now.

Not sure why did the lockdep think that this is same lock :-)

--srini
>
> Best regards,
> Krzysztof
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