linux-kernel - Re: [PATCH] regulator: core: avoid regulator_resolve

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Date:   Thu, 21 Jan 2021 21:30:39 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     David Collins <collinsd@...eaurora.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH] regulator: core: avoid regulator_resolve_supply() race
 condition

Hi Mark,

On 21.01.2021 16:44, Mark Brown wrote:
> On Thu, Jan 21, 2021 at 10:41:59AM +0100, Marek Szyprowski wrote:
>> On 18.01.2021 21:49, Mark Brown wrote:
>>> Does this help (completely untested):
>> Sadly nope. I get same warning:
> Try this instead:
>
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index 3ae5ccd9277d..31503776dbd7 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -1823,17 +1823,6 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
>   	if (rdev->supply)
>   		return 0;
>   
> -	/*
> -	 * Recheck rdev->supply with rdev->mutex lock held to avoid a race
> -	 * between rdev->supply null check and setting rdev->supply in
> -	 * set_supply() from concurrent tasks.
> -	 */
> -	regulator_lock(rdev);
> -
> -	/* Supply just resolved by a concurrent task? */
> -	if (rdev->supply)
> -		goto out;
> -
>   	r = regulator_dev_lookup(dev, rdev->supply_name);
>   	if (IS_ERR(r)) {
>   		ret = PTR_ERR(r);
> @@ -1885,12 +1874,29 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
>   		goto out;
>   	}
>   
> +	/*
> +	 * Recheck rdev->supply with rdev->mutex lock held to avoid a race
> +	 * between rdev->supply null check and setting rdev->supply in
> +	 * set_supply() from concurrent tasks.
> +	 */
> +	regulator_lock(rdev);
> +
> +	/* Supply just resolved by a concurrent task? */
> +	if (rdev->supply) {
> +		regulator_unlock(rdev);
> +		put_device(&r->dev);
> +		return ret;
> +	}
> +
>   	ret = set_supply(rdev, r);
>   	if (ret < 0) {
> +		regulator_unlock(rdev);
>   		put_device(&r->dev);
> -		goto out;
> +		return ret;
>   	}
>   
> +	regulator_unlock(rdev);
> +
>   	/*
>   	 * In set_machine_constraints() we may have turned this regulator on
>   	 * but we couldn't propagate to the supply if it hadn't been resolved
> @@ -1901,12 +1907,11 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
>   		if (ret < 0) {
>   			_regulator_put(rdev->supply);
>   			rdev->supply = NULL;
> -			goto out;
> +			goto out_rdev_lock;

drivers/regulator/core.c:1910:4: error: label ‘out_rdev_lock’ used but 
not defined

>   		}
>   	}
>   
>   out:
> -	regulator_unlock(rdev);
>   	return ret;
>   }
>   

It looks that it finally fixes the locking issue, with the above goto 
removed completely to fix build. Feel free to add:

Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

Best regards

-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland