[PATCH 1/2] leds: lm3530: use brightness_set_blocking for sleepable callback

[Runyu Xiao]

lm3530_brightness_set() talks to the device over I2C and can sleep, but
the driver registers it as brightness_set.  That leaves the LED core
free to invoke the callback from atomic contexts.

This issue was found by our static analysis tool and then manually
reviewed against the current tree.

A minimal Lockdep reproducer that keeps the original registration and
call chain is enough to trigger the warning: lm3530_probe() still
publishes lm3530_brightness_set() as brightness_set,
led_trigger_event_atomic() invokes it under spin_lock_irqsave(), and
the callback reaches i2c_smbus_write_byte_data() as its first
sleepable edge.

Lockdep reports:

  BUG: sleeping function called from invalid context
  i2c_smbus_write_byte_data.constprop.0+0x14/0x30 [vuln_msv]
  lm3530_brightness_set+0x4e/0x66 [vuln_msv]
  led_trigger_event_atomic.constprop.0+0x2b/0x40 [vuln_msv]

Convert the callback to brightness_set_blocking so the LED core only
invokes it from a sleepable context.

Fixes: b1e6b7068f02 ("leds: add driver for LM3530 ALS")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
---
Notes:
  - Validated with a grounded Lockdep PoC that preserves the
    lm3530_probe() brightness_set registration and the
    led_trigger_event_atomic() -> lm3530_brightness_set() ->
    i2c_smbus_write_byte_data() path.
  - checkpatch.pl --strict: clean.
  - Not tested on LM3530 hardware.

 drivers/leds/leds-lm3530.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/leds/leds-lm3530.c b/drivers/leds/leds-lm3530.c
index e44a3db106c3..ba744961ebcd 100644
--- a/drivers/leds/leds-lm3530.c
+++ b/drivers/leds/leds-lm3530.c
@@ -301,10 +301,11 @@ static int lm3530_init_registers(struct lm3530_data *drvdata)
 	return ret;
 }
 
-static void lm3530_brightness_set(struct led_classdev *led_cdev,
-				     enum led_brightness brt_val)
+static int
+lm3530_brightness_set_blocking(struct led_classdev *led_cdev,
+			       enum led_brightness brt_val)
 {
-	int err;
+	int err = 0;
 	struct lm3530_data *drvdata =
 	    container_of(led_cdev, struct lm3530_data, led_dev);
 	struct lm3530_platform_data *pdata = drvdata->pdata;
@@ -344,6 +345,8 @@ static void lm3530_brightness_set(struct led_classdev *led_cdev,
 	default:
 		break;
 	}
+
+	return err;
 }
 
 static ssize_t mode_show(struct device *dev,
@@ -438,7 +441,8 @@ static int lm3530_probe(struct i2c_client *client)
 	drvdata->brightness = LED_OFF;
 	drvdata->enable = false;
 	drvdata->led_dev.name = LM3530_LED_DEV;
-	drvdata->led_dev.brightness_set = lm3530_brightness_set;
+	drvdata->led_dev.brightness_set_blocking =
+		lm3530_brightness_set_blocking;
 	drvdata->led_dev.max_brightness = MAX_BRIGHTNESS;
 	drvdata->led_dev.groups = lm3530_groups;
 
-- 
2.34.1