linux-kernel - Re: [Outreachy kernel] [PATCH v2] staging: iio: ade7753: replace mlock with driver private lock

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Date:   Sun, 19 Mar 2017 00:16:46 +0530
From:   SIMRAN SINGHAL <singhalsimran0@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Alison Schofield <amsfield22@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Hartmut Knaack <knaack.h@....de>,
        Pete Meerwald-Stadler <pmeerw@...erw.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org,
        outreachy-kernel <outreachy-kernel@...glegroups.com>
Subject: Re: [Outreachy kernel] [PATCH v2] staging: iio: ade7753: replace
 mlock with driver private lock

On Sat, Mar 18, 2017 at 11:51 PM, Jonathan Cameron <jic23@...nel.org> wrote:
> On 18/03/17 17:34, SIMRAN SINGHAL wrote:
>> On Thu, Mar 16, 2017 at 3:23 AM, Jonathan Cameron <jic23@...nel.org> wrote:
>>> On 13/03/17 19:53, Alison Schofield wrote:
>>>> On Mon, Mar 13, 2017 at 10:01:07PM +0530, simran singhal wrote:
>>>>> The IIO subsystem is redefining iio_dev->mlock to be used by
>>>>> the IIO core only for protecting device operating mode changes.
>>>>> ie. Changes between INDIO_DIRECT_MODE, INDIO_BUFFER_* modes.
>>>>>
>>>>> In this driver, mlock was being used to protect hardware state
>>>>> changes.  Replace it with a lock in the devices global data.
>>>>>
>>>>> Fix some coding style issues related to white space also.
>>>>>
>>>>> Signed-off-by: simran singhal <singhalsimran0@...il.com>
>>>>> ---
>>>>>
>>>>>  v2:
>>>>>    -Removed new lock to reuse the existing lock
>>>> Simran,
>>>>
>>>> The good news is that you have 2 patches that have similar
>>>> challenges!  I'll suggest picking one, drive it to completion,
>>>> then do the other.
>>>>
>>>> This has the nested locking issue that Lars warned about.
>>>> Need to refactor to avoid.  Check back on his review comments.
>>>>
>>>> I suggest dropping those whitespace changes - they appear
>>>> out of place in this patch since you are no longer actually
>>>> touching those lines of code.
>>>>
>>>> alisons
>>> Also missing a mutex_init, though that may well become irrelevant
>>> with refactoring as suggested.
>>
>> Jonathon, what I found by looking at the codes of other drivers is that
>> we have to use mutex_init in probe function only.
>>
>> Is this correct?
> Yes, it only needs initializing once.
>>
So, no need of using mutex_init here as the function is not a
probe function.

Thanks
Simran

>> And this patch also suggest the same:-
>> https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=testing&id=388c8f18ff29fe95dbf72cb0a1bd8fbcd6f52f8f
>>
>>>>
>>>>
>>>>>
>>>>>  drivers/staging/iio/meter/ade7753.c | 12 ++++++------
>>>>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/drivers/staging/iio/meter/ade7753.c b/drivers/staging/iio/meter/ade7753.c
>>>>> index dfd8b71..d88eaa3 100644
>>>>> --- a/drivers/staging/iio/meter/ade7753.c
>>>>> +++ b/drivers/staging/iio/meter/ade7753.c
>>>>> @@ -83,10 +83,10 @@
>>>>>   * @buf_lock:       mutex to protect tx and rx
>>>>>   **/
>>>>>  struct ade7753_state {
>>>>> -        struct spi_device   *us;
>>>>> -                struct mutex        buf_lock;
>>>>> -                        u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>>> -                                u8          rx[ADE7753_MAX_RX];
>>>>> +    struct spi_device   *us;
>>>>> +    struct mutex        buf_lock;
>>>>> +    u8          tx[ADE7753_MAX_TX] ____cacheline_aligned;
>>>>> +    u8          rx[ADE7753_MAX_RX];
>>>>>  };
>>>>>
>>>>>  static int ade7753_spi_write_reg_8(struct device *dev,
>>>>> @@ -484,7 +484,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>>      if (!val)
>>>>>              return -EINVAL;
>>>>>
>>>>> -    mutex_lock(&indio_dev->mlock);
>>>>> +    mutex_lock(&st->buf_lock);
>>>>>
>>>>>      t = 27900 / val;
>>>>>      if (t > 0)
>>>>> @@ -505,7 +505,7 @@ static ssize_t ade7753_write_frequency(struct device *dev,
>>>>>      ret = ade7753_spi_write_reg_16(dev, ADE7753_MODE, reg);
>>>>>
>>>>>  out:
>>>>> -    mutex_unlock(&indio_dev->mlock);
>>>>> +    mutex_unlock(&st->buf_lock);
>>>>>
>>>>>      return ret ? ret : len;
>>>>>  }
>>>>> --
>>>>> 2.7.4
>>>>>
>>>>> --
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>>>
>