Add lock protection from race conditions in the 104-quad-8 counter
driver for differential encoder cable status changes. There is no IRQ
handling so spin_lock calls are used for protection.
Fixes: bbef69e088c3 ("counter: 104-quad-8: Support Differential Encoder
Cable Status")
Signed-off-by: Syed Nayyar Waris <[email protected]>
Split the patch from generic driver interface and clock prescaler
related code changes. Also, include more code statements for protection
using spin_lock calls and remove protection from few code statements as
they are unnecessary.
---
drivers/counter/104-quad-8.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 9dab190..1ce9660 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -1153,16 +1153,22 @@ static ssize_t quad8_signal_cable_fault_read(struct counter_device *counter,
{
const struct quad8_iio *const priv = counter->priv;
const size_t channel_id = signal->id / 2;
- const bool disabled = !(priv->cable_fault_enable & BIT(channel_id));
+ bool disabled;
unsigned int status;
unsigned int fault;
+ spin_lock(&((struct quad8_iio *)priv)->lock);
+
+ disabled = !(priv->cable_fault_enable & BIT(channel_id));
+
if (disabled)
return -EINVAL;
/* Logic 0 = cable fault */
status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
+ spin_unlock(&((struct quad8_iio *)priv)->lock);
+
/* Mask respective channel and invert logic */
fault = !(status & BIT(channel_id));
@@ -1194,6 +1200,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
if (ret)
return ret;
+ spin_lock(&priv->lock);
+
if (enable)
priv->cable_fault_enable |= BIT(channel_id);
else
@@ -1204,6 +1212,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
outb(cable_fault_enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
+ spin_unlock(&priv->lock);
+
return len;
}
--
2.7.4
On Thu, Mar 12, 2020 at 04:55:17PM +0530, Syed Nayyar Waris wrote:
> Add lock protection from race conditions in the 104-quad-8 counter
> driver for differential encoder cable status changes. There is no IRQ
> handling so spin_lock calls are used for protection.
>
> Fixes: bbef69e088c3 ("counter: 104-quad-8: Support Differential Encoder
> Cable Status")
>
> Signed-off-by: Syed Nayyar Waris <[email protected]>
>
> Split the patch from generic driver interface and clock prescaler
> related code changes. Also, include more code statements for protection
> using spin_lock calls and remove protection from few code statements as
> they are unnecessary.
> ---
Hello Syed,
Just like in the first patch, move these comments below the "---" line.
> drivers/counter/104-quad-8.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
> index 9dab190..1ce9660 100644
> --- a/drivers/counter/104-quad-8.c
> +++ b/drivers/counter/104-quad-8.c
> @@ -1153,16 +1153,22 @@ static ssize_t quad8_signal_cable_fault_read(struct counter_device *counter,
> {
> const struct quad8_iio *const priv = counter->priv;
> const size_t channel_id = signal->id / 2;
> - const bool disabled = !(priv->cable_fault_enable & BIT(channel_id));
> + bool disabled;
> unsigned int status;
> unsigned int fault;
>
> + spin_lock(&((struct quad8_iio *)priv)->lock);
You can redeclare priv whenever you need to avoid these casts:
struct quad8_iio *const priv = counter->priv;
...
spin_lock(&priv->lock);
...
spin_unlock(&priv->lock);
> +
> + disabled = !(priv->cable_fault_enable & BIT(channel_id));
> +
> if (disabled)
> return -EINVAL;
This return statement can cause a deadlock. You can avoid that by
calling spin_unlock before the return:
if (disabled) {
spin_unlock(&priv->lock);
return -EINVAL;
}
Sincerely,
William Breathitt Gray
>
> /* Logic 0 = cable fault */
> status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
>
> + spin_unlock(&((struct quad8_iio *)priv)->lock);
> +
> /* Mask respective channel and invert logic */
> fault = !(status & BIT(channel_id));
>
> @@ -1194,6 +1200,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
> if (ret)
> return ret;
>
> + spin_lock(&priv->lock);
> +
> if (enable)
> priv->cable_fault_enable |= BIT(channel_id);
> else
> @@ -1204,6 +1212,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
>
> outb(cable_fault_enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
>
> + spin_unlock(&priv->lock);
> +
> return len;
> }
>
> --
> 2.7.4
>