[PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Alexandru Ardelean]

From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock, to protect potential concurrent access to the
completion callback during a conversion.

Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 drivers/iio/adc/exynos_adc.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
index 7d23b6c33284..6a49f8dfab22 100644
--- a/drivers/iio/adc/exynos_adc.c
+++ b/drivers/iio/adc/exynos_adc.c
@@ -132,6 +132,8 @@ struct exynos_adc {
 
 	struct completion	completion;
 
+	struct mutex		lock;
+
 	u32			value;
 	unsigned int            version;
 
@@ -542,7 +544,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		return -EINVAL;
 	}
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	reinit_completion(&info->completion);
 
 	/* Select the channel to be used and Trigger conversion */
@@ -562,7 +564,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		ret = IIO_VAL_INT;
 	}
 
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -573,7 +575,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	unsigned long timeout;
 	int ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	info->read_ts = true;
 
 	reinit_completion(&info->completion);
@@ -598,7 +600,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	}
 
 	info->read_ts = false;
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -872,6 +874,8 @@ static int exynos_adc_probe(struct platform_device *pdev)
 	indio_dev->channels = exynos_adc_iio_channels;
 	indio_dev->num_channels = info->data->num_channels;
 
+	mutex_init(&info->lock);
+
 	ret = request_irq(info->irq, exynos_adc_isr,
 					0, dev_name(&pdev->dev), info);
 	if (ret < 0) {
-- 
2.25.1

Re: [PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Krzysztof Kozlowski]

On Wed, Aug 26, 2020 at 04:22:03PM +0300, Alexandru Ardelean wrote:
> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> 
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock, to protect potential concurrent access to the
> completion callback during a conversion.

I don't know the bigger picture (and no links here for general cleanup)
but I assume it is part of wider work and that mlock is unwanted. In
such case:

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>

If it is part of some bigger work, please put a link to lore.kernel.org
under separators ---, so everyone can get the context.


Best regards,
Krzysztof

> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
>  drivers/iio/adc/exynos_adc.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 

Re: [PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Alexandru Ardelean]

On Thu, Aug 27, 2020 at 9:57 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>
> On Wed, Aug 26, 2020 at 04:22:03PM +0300, Alexandru Ardelean wrote:
> > From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> >
> > As part of the general cleanup of indio_dev->mlock, this change replaces
> > it with a local lock, to protect potential concurrent access to the
> > completion callback during a conversion.
>
> I don't know the bigger picture (and no links here for general cleanup)
> but I assume it is part of wider work and that mlock is unwanted. In
> such case:
>
> Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
>
> If it is part of some bigger work, please put a link to lore.kernel.org
> under separators ---, so everyone can get the context.

Will keep that in mind.
I am not sure if there is a lore.kernel.org link that's easy to find
for a discussion on this topic, maybe I can describe it here and use
the link [from this later].

This was something that popped up during reviews we got from Jonathan
[or others], saying "please don't use indio_dev->mlock, that is an IIO
framework lock, and an IIO driver should not use it".
Reasons include [and some may be repeated a bit]:
- this could cause a deadlock if the IIO framework holds this lock and
an IIO driver also tries to get a hold of this lock
- similar to the previous point, this mlock is taken by
iio_device_claim_direct_mode() and released by
iio_device_release_direct_mode() ; which means that mlock aims to
become more of an IIO framework lock, than a general usage lock;
- this wasn't policed/reviewed intensely in the older driver [a few
years ago], but has become a point in recent reviews;
- if we want to develop/enhance the IIO framework, some elements like
this need to be taken care of, as more drivers get added and more
complexity gets added;
- there is an element of fairness [obviously], where someone writing a
new IIO driver, takes an older one as example, and gets hit on the
review; the person feels they did a good job in mimicking the old
driver; their feeling is correct; the IIO framework should provide
good references and/or cleanup existing drivers;
- same as the previous point, we don't want to keep telling people
writing new IIO drivers [and starting out with IIO] to "not use mlock
[because it was copied from an old driver]"; it's more/needless review
work


>
>
> Best regards,
> Krzysztof
>
> >
> > Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> > ---
> >  drivers/iio/adc/exynos_adc.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >

Re: [PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Thu, 27 Aug 2020 11:53:44 +0300
Alexandru Ardelean <ardeleanalex@gmail.com> wrote:

> On Thu, Aug 27, 2020 at 9:57 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> >
> > On Wed, Aug 26, 2020 at 04:22:03PM +0300, Alexandru Ardelean wrote:  
> > > From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> > >
> > > As part of the general cleanup of indio_dev->mlock, this change replaces
> > > it with a local lock, to protect potential concurrent access to the
> > > completion callback during a conversion.  
> >
> > I don't know the bigger picture (and no links here for general cleanup)
> > but I assume it is part of wider work and that mlock is unwanted. In
> > such case:
> >
> > Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
> >
> > If it is part of some bigger work, please put a link to lore.kernel.org
> > under separators ---, so everyone can get the context.  
> 
> Will keep that in mind.
> I am not sure if there is a lore.kernel.org link that's easy to find
> for a discussion on this topic, maybe I can describe it here and use
> the link [from this later].
> 
> This was something that popped up during reviews we got from Jonathan
> [or others], saying "please don't use indio_dev->mlock, that is an IIO
> framework lock, and an IIO driver should not use it".

Shortest one is the docs for that lock say don't use it directly in
a driver :)

https://elixir.bootlin.com/linux/latest/source/include/linux/iio/iio.h#L495

> Reasons include [and some may be repeated a bit]:
> - this could cause a deadlock if the IIO framework holds this lock and
> an IIO driver also tries to get a hold of this lock
> - similar to the previous point, this mlock is taken by
> iio_device_claim_direct_mode() and released by
> iio_device_release_direct_mode() ; which means that mlock aims to
> become more of an IIO framework lock, than a general usage lock;
> - this wasn't policed/reviewed intensely in the older driver [a few
> years ago], but has become a point in recent reviews;
> - if we want to develop/enhance the IIO framework, some elements like
> this need to be taken care of, as more drivers get added and more
> complexity gets added;

One side note here is we want to make all this [INTERN] state in 
struct iio_dev opaque to drivers.  It'll take a while as the boundary
gets crossed in various drivers.

> - there is an element of fairness [obviously], where someone writing a
> new IIO driver, takes an older one as example, and gets hit on the
> review; the person feels they did a good job in mimicking the old
> driver; their feeling is correct; the IIO framework should provide
> good references and/or cleanup existing drivers;
> - same as the previous point, we don't want to keep telling people
> writing new IIO drivers [and starting out with IIO] to "not use mlock
> [because it was copied from an old driver]"; it's more/needless review
> work

Good explanation.

Thanks,

Jonathan

> 
> 
> >
> >
> > Best regards,
> > Krzysztof
> >  
> > >
> > > Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> > > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> > > ---
> > >  drivers/iio/adc/exynos_adc.c | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > >  

Re: [PATCH] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Wed, 26 Aug 2020 16:22:03 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> 
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock, to protect potential concurrent access to the
> completion callback during a conversion.
> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Same comment as the other one about needing lock scope to be documented.

Otherwise looks good.  I thought we only had complicated uses of this
left, but clearly not :)

Jonathan

> ---
>  drivers/iio/adc/exynos_adc.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
> index 7d23b6c33284..6a49f8dfab22 100644
> --- a/drivers/iio/adc/exynos_adc.c
> +++ b/drivers/iio/adc/exynos_adc.c
> @@ -132,6 +132,8 @@ struct exynos_adc {
>  
>  	struct completion	completion;
>  
> +	struct mutex		lock;
> +
>  	u32			value;
>  	unsigned int            version;
>  
> @@ -542,7 +544,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
>  		return -EINVAL;
>  	}
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&info->lock);
>  	reinit_completion(&info->completion);
>  
>  	/* Select the channel to be used and Trigger conversion */
> @@ -562,7 +564,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
>  		ret = IIO_VAL_INT;
>  	}
>  
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&info->lock);
>  
>  	return ret;
>  }
> @@ -573,7 +575,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
>  	unsigned long timeout;
>  	int ret;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&info->lock);
>  	info->read_ts = true;
>  
>  	reinit_completion(&info->completion);
> @@ -598,7 +600,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
>  	}
>  
>  	info->read_ts = false;
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&info->lock);
>  
>  	return ret;
>  }
> @@ -872,6 +874,8 @@ static int exynos_adc_probe(struct platform_device *pdev)
>  	indio_dev->channels = exynos_adc_iio_channels;
>  	indio_dev->num_channels = info->data->num_channels;
>  
> +	mutex_init(&info->lock);
> +
>  	ret = request_irq(info->irq, exynos_adc_isr,
>  					0, dev_name(&pdev->dev), info);
>  	if (ret < 0) {

[PATCH v2] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Alexandru Ardelean]

From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>

As part of the general cleanup of indio_dev->mlock, this change replaces
it with a local lock, to protect potential concurrent access to the
completion callback during a conversion.

This is part of a bigger cleanup.
Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/

Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
 drivers/iio/adc/exynos_adc.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
index 20477b249f2a..99f4404e9fd1 100644
--- a/drivers/iio/adc/exynos_adc.c
+++ b/drivers/iio/adc/exynos_adc.c
@@ -138,6 +138,16 @@ struct exynos_adc {
 	bool			read_ts;
 	u32			ts_x;
 	u32			ts_y;
+
+	/*
+	 * Lock to protect from potential concurrent access to the
+	 * completion callback during a manual conversion. For this driver
+	 * a wait-callback is used to wait for the conversion result,
+	 * so in the meantime no other read request (or conversion start)
+	 * must be performed, otherwise it would interfere with the
+	 * current conversion result.
+	 */
+	struct mutex		lock;
 };
 
 struct exynos_adc_data {
@@ -542,7 +552,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		return -EINVAL;
 	}
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	reinit_completion(&info->completion);
 
 	/* Select the channel to be used and Trigger conversion */
@@ -562,7 +572,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
 		ret = IIO_VAL_INT;
 	}
 
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -573,7 +583,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	unsigned long timeout;
 	int ret;
 
-	mutex_lock(&indio_dev->mlock);
+	mutex_lock(&info->lock);
 	info->read_ts = true;
 
 	reinit_completion(&info->completion);
@@ -598,7 +608,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
 	}
 
 	info->read_ts = false;
-	mutex_unlock(&indio_dev->mlock);
+	mutex_unlock(&info->lock);
 
 	return ret;
 }
@@ -868,6 +878,8 @@ static int exynos_adc_probe(struct platform_device *pdev)
 	indio_dev->channels = exynos_adc_iio_channels;
 	indio_dev->num_channels = info->data->num_channels;
 
+	mutex_init(&info->lock);
+
 	ret = request_irq(info->irq, exynos_adc_isr,
 					0, dev_name(&pdev->dev), info);
 	if (ret < 0) {
-- 
2.17.1

Re: [PATCH v2] iio: adc: exynos_adc: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Wed, 16 Sep 2020 12:31:23 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> 
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock, to protect potential concurrent access to the
> completion callback during a conversion.
> 
> This is part of a bigger cleanup.
> Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/
> 
> Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Applied to the togreg branch of iio.git and pushed out as testing for the
autobuilders to play with it.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/exynos_adc.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
> index 20477b249f2a..99f4404e9fd1 100644
> --- a/drivers/iio/adc/exynos_adc.c
> +++ b/drivers/iio/adc/exynos_adc.c
> @@ -138,6 +138,16 @@ struct exynos_adc {
>  	bool			read_ts;
>  	u32			ts_x;
>  	u32			ts_y;
> +
> +	/*
> +	 * Lock to protect from potential concurrent access to the
> +	 * completion callback during a manual conversion. For this driver
> +	 * a wait-callback is used to wait for the conversion result,
> +	 * so in the meantime no other read request (or conversion start)
> +	 * must be performed, otherwise it would interfere with the
> +	 * current conversion result.
> +	 */
> +	struct mutex		lock;
>  };
>  
>  struct exynos_adc_data {
> @@ -542,7 +552,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
>  		return -EINVAL;
>  	}
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&info->lock);
>  	reinit_completion(&info->completion);
>  
>  	/* Select the channel to be used and Trigger conversion */
> @@ -562,7 +572,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
>  		ret = IIO_VAL_INT;
>  	}
>  
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&info->lock);
>  
>  	return ret;
>  }
> @@ -573,7 +583,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
>  	unsigned long timeout;
>  	int ret;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&info->lock);
>  	info->read_ts = true;
>  
>  	reinit_completion(&info->completion);
> @@ -598,7 +608,7 @@ static int exynos_read_s3c64xx_ts(struct iio_dev *indio_dev, int *x, int *y)
>  	}
>  
>  	info->read_ts = false;
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&info->lock);
>  
>  	return ret;
>  }
> @@ -868,6 +878,8 @@ static int exynos_adc_probe(struct platform_device *pdev)
>  	indio_dev->channels = exynos_adc_iio_channels;
>  	indio_dev->num_channels = info->data->num_channels;
>  
> +	mutex_init(&info->lock);
> +
>  	ret = request_irq(info->irq, exynos_adc_isr,
>  					0, dev_name(&pdev->dev), info);
>  	if (ret < 0) {