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Message-ID: <CAOCi2DF4T6MOVy5=UJ=K3mcpUt7pA_8KRO0JM=ejqfxvMY0MXw@mail.gmail.com>
Date: Sun, 19 Mar 2017 22:44:38 +0530
From: Gargi Sharma <gs051095@...il.com>
To: simran singhal <singhalsimran0@...il.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>,
Hartmut Knaack <knaack.h@....de>,
Peter 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@...glegroups.com
Subject: Re: [Outreachy kernel] [PATCH v5] staging: Use buf_lock instead of
mlock and Refactor code
On Sun, Mar 19, 2017 at 6:20 PM, simran singhal
<singhalsimran0@...il.com> 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 buf_lock in the devices global data.
>
> As buf_lock protects both the adis16060_spi_write() and
> adis16060_spi_read() functions and both are always called in
> pair. First write, then read. Thus, refactor the code to have
> one single function adis16060_spi_write_than_read() which is
> protected by the existing buf_lock.
>
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
> ---
>
> v5:
> -Rename val in adis16060_spi_write_than_read() to conf.
> -Rename val2 in adis16060_spi_write_than_read() to val.
> -Corrected Checkpatch issues.
> -Removed goto from adis16060_read_raw().
>
>
> drivers/staging/iio/gyro/adis16060_core.c | 42 ++++++++++++-------------------
> 1 file changed, 16 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/staging/iio/gyro/adis16060_core.c b/drivers/staging/iio/gyro/adis16060_core.c
> index c9d46e7..0f12492 100644
> --- a/drivers/staging/iio/gyro/adis16060_core.c
> +++ b/drivers/staging/iio/gyro/adis16060_core.c
> @@ -40,25 +40,20 @@ struct adis16060_state {
>
> static struct iio_dev *adis16060_iio_dev;
>
> -static int adis16060_spi_write(struct iio_dev *indio_dev, u8 val)
> +static int adis16060_spi_write_than_read(struct iio_dev *indio_dev,
> + u8 conf, u16 *val)
> {
> int ret;
> struct adis16060_state *st = iio_priv(indio_dev);
>
> mutex_lock(&st->buf_lock);
> - st->buf[2] = val; /* The last 8 bits clocked in are latched */
> + st->buf[2] = conf; /* The last 8 bits clocked in are latched */
> ret = spi_write(st->us_w, st->buf, 3);
> - mutex_unlock(&st->buf_lock);
>
> - return ret;
> -}
> -
> -static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val)
> -{
> - int ret;
> - struct adis16060_state *st = iio_priv(indio_dev);
> -
> - mutex_lock(&st->buf_lock);
> + if (ret < 0) {
> + mutex_unlock(&st->buf_lock);
> + return ret;
> + }
>
> ret = spi_read(st->us_r, st->buf, 3);
>
> @@ -69,8 +64,8 @@ static int adis16060_spi_read(struct iio_dev *indio_dev, u16 *val)
> */
> if (!ret)
> *val = ((st->buf[0] & 0x3) << 12) |
> - (st->buf[1] << 4) |
> - ((st->buf[2] >> 4) & 0xF);
> + (st->buf[1] << 4) |
> + ((st->buf[2] >> 4) & 0xF);
> mutex_unlock(&st->buf_lock);
>
> return ret;
> @@ -83,20 +78,19 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
> {
> u16 tval = 0;
> int ret;
> + struct adis16060_state *st = iio_priv(indio_dev);
>
> switch (mask) {
> case IIO_CHAN_INFO_RAW:
> /* Take the iio_dev status lock */
> - mutex_lock(&indio_dev->mlock);
> - ret = adis16060_spi_write(indio_dev, chan->address);
> + mutex_lock(&st->buf_lock);
> + ret = adis16060_spi_write_than_read(indio_dev,
> + chan->address, &tval);
> if (ret < 0)
> - goto out_unlock;
> + mutex_unlock(&st->buf_lock);
> + return ret;
>
> - ret = adis16060_spi_read(indio_dev, &tval);
> - if (ret < 0)
> - goto out_unlock;
> -
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&st->buf_lock);
> *val = tval;
> return IIO_VAL_INT;
> case IIO_CHAN_INFO_OFFSET:
> @@ -110,10 +104,6 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
> }
>
> return -EINVAL;
> -
> -out_unlock:
> - mutex_unlock(&indio_dev->mlock);
> - return ret;
> }
>
Hey Simran,
I'm another Outreachy aspirant and I'm trying to work through a
similar patch in another driver. Can you please explain to me how you
are avoiding nested locks here? From what I understand, the function
adis16060_read_raw call a lock on &st->buf_lock and then you call the
function adis16060_spi_write_than_read which again tries to get hold
of the same lock. Isn't this a deadlock situation? Please let me know
if my understanding is incorrect.
Thank you!
Gargi
> static const struct iio_info adis16060_info = {
> --
> 2.7.4
>
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