On Sat, Mar 18, 2017 at 11:08 PM, Gargi Sharma <gs051095@xxxxxxxxx> wrote:
> On Fri, Mar 17, 2017 at 10:41 PM, Alison Schofield <amsfield22@xxxxxxxxx> wrote:
>>
>> On Fri, Mar 17, 2017 at 08:41:11PM +0530, sayli karnik wrote:
>> > iio_dev->mlock should be used by the IIO core only for protecting
>> > device operating mode changes. ie. Changes between INDIO_DIRECT_MODE,
>> > INDIO_BUFFER_* modes.
>> > Replace mlock with a lock in the device's global data to protect
>> > hardware state changes.
>>
>> Hi Sayli,
>>
>> There are nested locks here, hence deadlock. I'm wondering if we can grab
>> the lock once at the top layers (read/write_raw functions) and hold it.
>> Seems like that's a pattern in IIO drivers. Let's see what the reviewers
>> suggest on this one.
>>
>
To avoid the mutex lock nesting, should I remove the locking in
ade7758_{read, write}_raw() or
ade7758_spi_{read, write}_reg_8() ?
I think removing it from the outer function i.e ade7758_{read,
write}_raw() is safer so that other places
where ade7758_spi_{read, write}_reg_8() might be used are unaffected.
thanks,
sayli
> Hey Alison,
>
> I was trying to work through a similar patch. I'm having trouble
> understanding how a deadlock will be created? Also, Lars suggested in
> this{https://groups.google.com/forum/#!msg/outreachy-kernel/GapBLSp5WCo/cju_A8B-AwAJ}
> thread that writing a variant of
> <driver_name>_spi_{read,write}_reg_16() that does not take a lock and
> instead uses read-modify-write cycle in a protected section is the way
> to go. Is there any example I can look to for inspiration :). Also, in
> similar vain there are other(8 bit) variants for read/write functions
> as well. Should they be modified as well?
>
> Thanks!
> Gargi
>
>> alisons
>>
>> >
>> > Signed-off-by: sayli karnik <karniksayli1995@xxxxxxxxx>
>> > ---
>> > drivers/staging/iio/meter/ade7758_core.c | 10 ++++++----
>> > 1 file changed, 6 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/drivers/staging/iio/meter/ade7758_core.c b/drivers/staging/iio/meter/ade7758_core.c
>> > index 99c89e6..1723eb8 100644
>> > --- a/drivers/staging/iio/meter/ade7758_core.c
>> > +++ b/drivers/staging/iio/meter/ade7758_core.c
>> > @@ -522,13 +522,14 @@ static int ade7758_read_raw(struct iio_dev *indio_dev,
>> > int *val2,
>> > long mask)
>> > {
>> > + struct ade7758_state *st = iio_priv(indio_dev);
>> > int ret;
>> >
>> > switch (mask) {
>> > case IIO_CHAN_INFO_SAMP_FREQ:
>> > - mutex_lock(&indio_dev->mlock);
>> > + mutex_lock(&st->buf_lock);
>> > ret = ade7758_read_samp_freq(&indio_dev->dev, val);
>> > - mutex_unlock(&indio_dev->mlock);
>> > + mutex_unlock(&st->buf_lock);
>> > return ret;
>> > default:
>> > return -EINVAL;
>> > @@ -541,15 +542,16 @@ static int ade7758_write_raw(struct iio_dev *indio_dev,
>> > struct iio_chan_spec const *chan,
>> > int val, int val2, long mask)
>> > {
>> > + struct ade7758_state *st = iio_priv(indio_dev);
>> > int ret;
>> >
>> > switch (mask) {
>> > case IIO_CHAN_INFO_SAMP_FREQ:
>> > if (val2)
>> > return -EINVAL;
>> > - mutex_lock(&indio_dev->mlock);
>> > + mutex_lock(&st->buf_lock);
>> > ret = ade7758_write_samp_freq(&indio_dev->dev, val);
>> > - mutex_unlock(&indio_dev->mlock);
>> > + mutex_unlock(&st->buf_lock);
>> > return ret;
>> > default:
>> > return -EINVAL;
>> > --
>> > 2.7.4
>> >
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