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

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Message-ID: <6e2b0fa2-948e-007b-3d2b-9ad71357af03@kernel.org>
Date:   Sat, 18 Mar 2017 18:21:14 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     SIMRAN SINGHAL <singhalsimran0@...il.com>
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 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.
> 
> 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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>>