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SubjectRe: [PATCH] regulator: core: avoid regulator_resolve_supply() race condition
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Hello Mark,

On 1/21/21 12:30 PM, Marek Szyprowski wrote:
> 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@samsung.com>
>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

Thank you for making this fix. I'm sorry that I missed the potential
deadlock issue resulting from the regulator_enable() call inside
regulator_resolve_supply() with rdev->mutex locked. Your fix avoids
deadlock while still ensuring that the there isn't a set supply race
condition.

Take care,
David

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

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