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

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Message-ID: <CALrZqyNLCzJm3N0aryTiRJfQmeB6G2jztfV73dFQ2bR5Zycs_A@mail.gmail.com>
Date:   Sat, 18 Mar 2017 23:04:05 +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 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?

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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>