[PATCH v5] iio: imu: kmx61: Use guard(mutex)() over manual locking

[PATCH v5] iio: imu: kmx61: Use guard(mutex)() over manual locking

[Maxwell Doose]

Include linux/cleanup.h to take advantage of new macros.

Replace manual mutex_lock() and mutex_unlock() calls across the file
with guard(mutex)() and scoped_guard() where appropriate to simplify
error paths and eliminate manual locking calls.

Add new helper function kmx61_read_for_each_active_channel() to mitigate
certain style issues and to prevent notifying that the IRQ is finished
whilst holding the lock.

Update certain returns, and add default case to return -EINVAL in
kmx61_read_raw().

Remove now-redundant gotos and ret variables, as the new RAII macros
make them unneeded.

Signed-off-by: Maxwell Doose <m32285159@gmail.com>
---
 v2:
 - Remove redundant blank line per Andy.
 - Put kmx61_set_mode() function call in kmx61_runtime_suspend() on one
   line per Andy.

 v3:
 - Add dedicated scope for guards.

 v4:
 - Fix certain scoping in switch-case blocks.
 - Remove stray ret variable.
 - Used scoped_guard() in kmx61_trigger_handler() instead of guard()().

 v5:
 - Added new helper function kmx61_read_for_each_active_channel() per
   Jonathan's suggestion.
 - Add default case to return -EINVAL in kmx61_read_raw() per Andy's
   suggestion.
 - Add blank lines between guard(mutex)() calls and regular code per
   Andy's suggestion.
 - Change last return statement of kmx61_write_event_config() to be 0
   per Jonathan's suggestion.


 drivers/iio/imu/kmx61.c | 125 +++++++++++++++++++++-------------------
 1 file changed, 66 insertions(+), 59 deletions(-)

diff --git a/drivers/iio/imu/kmx61.c b/drivers/iio/imu/kmx61.c
index 3cd91d8a89ee..fe3f357c8889 100644
--- a/drivers/iio/imu/kmx61.c
+++ b/drivers/iio/imu/kmx61.c
@@ -7,6 +7,7 @@
  * IIO driver for KMX61 (7-bit I2C slave address 0x0E or 0x0F).
  */
 
+#include <linux/cleanup.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/mod_devicetable.h>
@@ -783,7 +784,7 @@ static int kmx61_read_raw(struct iio_dev *indio_dev,
 	struct kmx61_data *data = kmx61_get_data(indio_dev);
 
 	switch (mask) {
-	case IIO_CHAN_INFO_RAW:
+	case IIO_CHAN_INFO_RAW: {
 		switch (chan->type) {
 		case IIO_ACCEL:
 			base_reg = KMX61_ACC_XOUT_L;
@@ -794,28 +795,24 @@ static int kmx61_read_raw(struct iio_dev *indio_dev,
 		default:
 			return -EINVAL;
 		}
-		mutex_lock(&data->lock);
+		guard(mutex)(&data->lock);
 
 		ret = kmx61_set_power_state(data, true, chan->address);
-		if (ret) {
-			mutex_unlock(&data->lock);
+		if (ret)
 			return ret;
-		}
 
 		ret = kmx61_read_measurement(data, base_reg, chan->scan_index);
 		if (ret < 0) {
 			kmx61_set_power_state(data, false, chan->address);
-			mutex_unlock(&data->lock);
 			return ret;
 		}
 		*val = sign_extend32(ret >> chan->scan_type.shift,
 				     chan->scan_type.realbits - 1);
 		ret = kmx61_set_power_state(data, false, chan->address);
-
-		mutex_unlock(&data->lock);
 		if (ret)
 			return ret;
 		return IIO_VAL_INT;
+	}
 	case IIO_CHAN_INFO_SCALE:
 		switch (chan->type) {
 		case IIO_ACCEL:
@@ -834,41 +831,41 @@ static int kmx61_read_raw(struct iio_dev *indio_dev,
 		if (chan->type != IIO_ACCEL && chan->type != IIO_MAGN)
 			return -EINVAL;
 
-		mutex_lock(&data->lock);
-		ret = kmx61_get_odr(data, val, val2, chan->address);
-		mutex_unlock(&data->lock);
+		scoped_guard(mutex, &data->lock)
+			ret = kmx61_get_odr(data, val, val2, chan->address);
 		if (ret)
 			return -EINVAL;
 		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
 	}
-	return -EINVAL;
+
 }
 
 static int kmx61_write_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan, int val,
 			   int val2, long mask)
 {
-	int ret;
 	struct kmx61_data *data = kmx61_get_data(indio_dev);
 
 	switch (mask) {
-	case IIO_CHAN_INFO_SAMP_FREQ:
+	case IIO_CHAN_INFO_SAMP_FREQ: {
 		if (chan->type != IIO_ACCEL && chan->type != IIO_MAGN)
 			return -EINVAL;
 
-		mutex_lock(&data->lock);
-		ret = kmx61_set_odr(data, val, val2, chan->address);
-		mutex_unlock(&data->lock);
-		return ret;
+		guard(mutex)(&data->lock);
+
+		return kmx61_set_odr(data, val, val2, chan->address);
+	}
 	case IIO_CHAN_INFO_SCALE:
 		switch (chan->type) {
-		case IIO_ACCEL:
+		case IIO_ACCEL: {
 			if (val != 0)
 				return -EINVAL;
-			mutex_lock(&data->lock);
-			ret = kmx61_set_scale(data, val2);
-			mutex_unlock(&data->lock);
-			return ret;
+			guard(mutex)(&data->lock);
+
+			return kmx61_set_scale(data, val2);
+		}
 		default:
 			return -EINVAL;
 		}
@@ -945,29 +942,26 @@ static int kmx61_write_event_config(struct iio_dev *indio_dev,
 	if (state && data->ev_enable_state)
 		return 0;
 
-	mutex_lock(&data->lock);
+	guard(mutex)(&data->lock);
 
 	if (!state && data->motion_trig_on) {
 		data->ev_enable_state = false;
-		goto err_unlock;
+		return ret;
 	}
 
 	ret = kmx61_set_power_state(data, state, KMX61_ACC);
 	if (ret < 0)
-		goto err_unlock;
+		return ret;
 
 	ret = kmx61_setup_any_motion_interrupt(data, state);
 	if (ret < 0) {
 		kmx61_set_power_state(data, false, KMX61_ACC);
-		goto err_unlock;
+		return ret;
 	}
 
 	data->ev_enable_state = state;
 
-err_unlock:
-	mutex_unlock(&data->lock);
-
-	return ret;
+	return 0;
 }
 
 static int kmx61_acc_validate_trigger(struct iio_dev *indio_dev,
@@ -1020,11 +1014,11 @@ static int kmx61_data_rdy_trigger_set_state(struct iio_trigger *trig,
 	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
 	struct kmx61_data *data = kmx61_get_data(indio_dev);
 
-	mutex_lock(&data->lock);
+	guard(mutex)(&data->lock);
 
 	if (!state && data->ev_enable_state && data->motion_trig_on) {
 		data->motion_trig_on = false;
-		goto err_unlock;
+		return ret;
 	}
 
 	if (data->acc_dready_trig == trig || data->motion_trig == trig)
@@ -1034,7 +1028,7 @@ static int kmx61_data_rdy_trigger_set_state(struct iio_trigger *trig,
 
 	ret = kmx61_set_power_state(data, state, device);
 	if (ret < 0)
-		goto err_unlock;
+		return ret;
 
 	if (data->acc_dready_trig == trig || data->mag_dready_trig == trig)
 		ret = kmx61_setup_new_data_interrupt(data, state, device);
@@ -1042,7 +1036,7 @@ static int kmx61_data_rdy_trigger_set_state(struct iio_trigger *trig,
 		ret = kmx61_setup_any_motion_interrupt(data, state);
 	if (ret < 0) {
 		kmx61_set_power_state(data, false, device);
-		goto err_unlock;
+		return ret;
 	}
 
 	if (data->acc_dready_trig == trig)
@@ -1051,8 +1045,6 @@ static int kmx61_data_rdy_trigger_set_state(struct iio_trigger *trig,
 		data->mag_dready_trig_on = state;
 	else
 		data->motion_trig_on = state;
-err_unlock:
-	mutex_unlock(&data->lock);
 
 	return ret;
 }
@@ -1181,30 +1173,52 @@ static irqreturn_t kmx61_data_rdy_trig_poll(int irq, void *private)
 	return IRQ_HANDLED;
 }
 
-static irqreturn_t kmx61_trigger_handler(int irq, void *p)
+/**
+ * kmx61_read_for_each_active_channel() - Read each active channel into a buffer
+ *
+ * @indio_dev: IIO Device struct to read from
+ * @buffer: Destination buffer to write to, the array must be of at least size 8
+ *
+ * Intended only for use in kmx61_trigger_handler().
+ *
+ * Return:
+ * 0 on success, negative errno on failure.
+ */
+static int kmx61_read_for_each_active_channel(struct iio_dev *indio_dev, s16 *buffer)
 {
-	struct iio_poll_func *pf = p;
-	struct iio_dev *indio_dev = pf->indio_dev;
 	struct kmx61_data *data = kmx61_get_data(indio_dev);
-	int bit, ret, i = 0;
 	u8 base;
-	s16 buffer[8] = { };
+	int ret, bit;
+	int i = 0;
 
 	if (indio_dev == data->acc_indio_dev)
 		base = KMX61_ACC_XOUT_L;
 	else
 		base = KMX61_MAG_XOUT_L;
 
-	mutex_lock(&data->lock);
+	guard(mutex)(&data->lock);
+
 	iio_for_each_active_channel(indio_dev, bit) {
 		ret = kmx61_read_measurement(data, base, bit);
 		if (ret < 0) {
-			mutex_unlock(&data->lock);
-			goto err;
+			return ret;
 		}
 		buffer[i++] = ret;
 	}
-	mutex_unlock(&data->lock);
+
+	return 0;
+}
+
+static irqreturn_t kmx61_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	int ret;
+	s16 buffer[8] = { };
+
+	ret = kmx61_read_for_each_active_channel(indio_dev, buffer);
+	if (ret < 0)
+		goto err;
 
 	iio_push_to_buffers(indio_dev, buffer);
 err:
@@ -1419,22 +1433,18 @@ static void kmx61_remove(struct i2c_client *client)
 		iio_trigger_unregister(data->motion_trig);
 	}
 
-	mutex_lock(&data->lock);
+	guard(mutex)(&data->lock);
+
 	kmx61_set_mode(data, KMX61_ALL_STBY, KMX61_ACC | KMX61_MAG, true);
-	mutex_unlock(&data->lock);
 }
 
 static int kmx61_suspend(struct device *dev)
 {
-	int ret;
 	struct kmx61_data *data = i2c_get_clientdata(to_i2c_client(dev));
 
-	mutex_lock(&data->lock);
-	ret = kmx61_set_mode(data, KMX61_ALL_STBY, KMX61_ACC | KMX61_MAG,
-			     false);
-	mutex_unlock(&data->lock);
+	guard(mutex)(&data->lock);
 
-	return ret;
+	return kmx61_set_mode(data, KMX61_ALL_STBY, KMX61_ACC | KMX61_MAG, false);
 }
 
 static int kmx61_resume(struct device *dev)
@@ -1453,13 +1463,10 @@ static int kmx61_resume(struct device *dev)
 static int kmx61_runtime_suspend(struct device *dev)
 {
 	struct kmx61_data *data = i2c_get_clientdata(to_i2c_client(dev));
-	int ret;
 
-	mutex_lock(&data->lock);
-	ret = kmx61_set_mode(data, KMX61_ALL_STBY, KMX61_ACC | KMX61_MAG, true);
-	mutex_unlock(&data->lock);
+	guard(mutex)(&data->lock);
 
-	return ret;
+	return kmx61_set_mode(data, KMX61_ALL_STBY, KMX61_ACC | KMX61_MAG, true);
 }
 
 static int kmx61_runtime_resume(struct device *dev)
-- 
2.54.0

Re: [PATCH v5] iio: imu: kmx61: Use guard(mutex)() over manual locking

[Maxwell Doose]

Hi Jonathan,

On Thu, May 7, 2026 at 5:33 PM Maxwell Doose <m32285159@gmail.com> wrote:
>
[snip]
> @@ -945,29 +942,26 @@ static int kmx61_write_event_config(struct iio_dev *indio_dev,
>         if (state && data->ev_enable_state)
>                 return 0;
>
> -       mutex_lock(&data->lock);
> +       guard(mutex)(&data->lock);
>

Correct me if I'm wrong but this looks like a TOCTOU race, was
reported by sashiko at
https://sashiko.dev/#/patchset/20260507223337.48437-1-m32285159%40gmail.com.
If this is a confirmed race I'll get a fix out this evening.

best regards,
max

Re: [PATCH v5] iio: imu: kmx61: Use guard(mutex)() over manual locking

[Jonathan Cameron]

On Fri, 8 May 2026 08:03:45 -0500
Maxwell Doose <m32285159@gmail.com> wrote:

> Hi Jonathan,
> 
> On Thu, May 7, 2026 at 5:33 PM Maxwell Doose <m32285159@gmail.com> wrote:
> >  
> [snip]
> > @@ -945,29 +942,26 @@ static int kmx61_write_event_config(struct iio_dev *indio_dev,
> >         if (state && data->ev_enable_state)
> >                 return 0;
> >
> > -       mutex_lock(&data->lock);
> > +       guard(mutex)(&data->lock);
> >  
> 
> Correct me if I'm wrong but this looks like a TOCTOU race, was
> reported by sashiko at
> https://sashiko.dev/#/patchset/20260507223337.48437-1-m32285159%40gmail.com.
> If this is a confirmed race I'll get a fix out this evening.
Indeed looks like a correct report.

Take your time though. I'm swamped anyway so will be a while before
I get to any new patches (probably!)

> 
> best regards,
> max

Re: [PATCH v5] iio: imu: kmx61: Use guard(mutex)() over manual locking

[Maxwell Doose]

On Mon, May 11, 2026 at 12:17 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Fri, 8 May 2026 08:03:45 -0500
> Maxwell Doose <m32285159@gmail.com> wrote:
>
> > Hi Jonathan,
> >
> > On Thu, May 7, 2026 at 5:33 PM Maxwell Doose <m32285159@gmail.com> wrote:
> > >
> > [snip]
> > > @@ -945,29 +942,26 @@ static int kmx61_write_event_config(struct iio_dev *indio_dev,
> > >         if (state && data->ev_enable_state)
> > >                 return 0;
> > >
> > > -       mutex_lock(&data->lock);
> > > +       guard(mutex)(&data->lock);
> > >
> >
> > Correct me if I'm wrong but this looks like a TOCTOU race, was
> > reported by sashiko at
> > https://sashiko.dev/#/patchset/20260507223337.48437-1-m32285159%40gmail.com.
> > If this is a confirmed race I'll get a fix out this evening.
> Indeed looks like a correct report.
>
> Take your time though. I'm swamped anyway so will be a while before
> I get to any new patches (probably!)
>

Alrighty sounds good. Dunno if we merge this or not and then send the
fix just in case or if I base it off of the original. Former seems
preferable.

best regards,
max



> >
> > best regards,
> > max
>