linux-kernel - Re: [Outreachy kernel] [PATCH v3] staging: adis16060_core: Use private driver lock instead of mlock

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Message-ID: <20170313193003.GB5941@d830.WORKGROUP>
Date:   Mon, 13 Mar 2017 12:30:04 -0700
From:   Alison Schofield <amsfield22@...il.com>
To:     simran singhal <singhalsimran0@...il.com>
Cc:     lars@...afoo.de, Michael.Hennerich@...log.com, 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 v3] staging: adis16060_core: Use
 private driver lock instead of mlock

On Mon, Mar 13, 2017 at 11:41:30PM +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.
> 
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
> ---
>  
>  v3:
>    -Removed new lock to reuse the existing lock

Hi Simran,

Check Lars review comments about refactoring into a
write_then_read function protected by same buf_lock.

As it is now, it'll deadlock on buf_lock. It locks in
_read_raw and then calls _spi_write where an attempt
is made to grab the same lock.

alisons


> 
>  drivers/staging/iio/gyro/adis16060_core.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/iio/gyro/adis16060_core.c b/drivers/staging/iio/gyro/adis16060_core.c
> index c9d46e7..602ec53 100644
> --- a/drivers/staging/iio/gyro/adis16060_core.c
> +++ b/drivers/staging/iio/gyro/adis16060_core.c
> @@ -83,11 +83,12 @@ 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);
> +		mutex_lock(&st->buf_lock);
>  		ret = adis16060_spi_write(indio_dev, chan->address);
>  		if (ret < 0)
>  			goto out_unlock;
> @@ -96,7 +97,7 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
>  		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:
> @@ -112,7 +113,7 @@ static int adis16060_read_raw(struct iio_dev *indio_dev,
>  	return -EINVAL;
>  
>  out_unlock:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->buf_lock);
>  	return ret;
>  }
>  
> -- 
> 2.7.4
> 
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