linux-kernel - Re: [PATCH] regulator: core: Avoid debugfs: Directory ... already present! error

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Date:   Sat, 23 Jan 2021 12:57:31 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: core: Avoid debugfs: Directory ... already
 present! error

Hi,

On 1/23/21 11:29 AM, Charles Keepax wrote:
> On Fri, Jan 22, 2021 at 07:32:50PM +0100, Hans de Goede wrote:
>> Sometimes regulator_get() gets called twice for the same supply on the
>> same device. This may happen e.g. when a framework / library is used
>> which uses the regulator; and the driver itself also needs to enable
>> the regulator in some cases where the framework will not enable it.
>>
>> Commit ff268b56ce8c ("regulator: core: Don't spew backtraces on
>> duplicate sysfs") already takes care of the backtrace which would
>> trigger when creating a duplicate consumer symlink under
>> /sys/class/regulator/regulator.%d in this scenario.
>>
>> Commit c33d442328f5 ("debugfs: make error message a bit more verbose")
>> causes a new error to get logged in this scenario:
>>
>> [   26.938425] debugfs: Directory 'wm5102-codec-MICVDD' with parent 'spi-WM510204:00-MICVDD' already present!
>>
>> There is no _nowarn variant of debugfs_create_dir(), but we can detect
>> and avoid this problem by checking the return value of the earlier
>> sysfs_create_link_nowarn() call.
>>
>> Add a check for the earlier sysfs_create_link_nowarn() failing with
>> -EEXIST and skip the debugfs_create_dir() call in that case, avoiding
>> this error getting logged.
>>
>> Fixes: c33d442328f5 ("debugfs: make error message a bit more verbose")
>> Cc: Charles Keepax <ckeepax@...nsource.cirrus.com>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
> 
> Reviewed-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> 
> Thanks,
> Charles
> 
>> -	int err;
>> +	int err = 0;
>>  
>> @@ -1663,8 +1663,8 @@ static struct regulator *create_regulator(struct regulator_dev *rdev,
>>  
>> -	regulator->debugfs = debugfs_create_dir(supply_name,
>> -						rdev->debugfs);
>> +	if (err != -EEXIST)
>> +		regulator->debugfs = debugfs_create_dir(supply_name, rdev->debugfs);
> 
> There is a slight oddity here in that if this regulator has
> no struct device we will still get the warning. However, I
> am totally not clear on when/why a regulator might not have a
> dev, and am fairly sure it isn't common. So my vote would be
> to cross that bridge if we ever come to it.

Yes, I expect the combination of having 2 consumers which both get the
regulator with a NULL device pointer to be very rare and hopefully
it does not happen at all.

Regards,

Hans