[PATCH v4 6/7] gpiolib: cdev: don't report a failed line read as an edge

[Adrian Ambrozewicz <aambrozewicz@nvidia.com>]

With both edges requested, the IRQ threads read the line to tell a
rising edge from a falling one, and report any non-zero result as
rising, an error included. A read fails when a hot-pluggable chip is
going away, or when gpiochip_remove() has cleared gdev->chip before the
IRQ is freed.

Drop the event when the read fails, as debounce_work_func() does.

Reproduced with gpio-sim and a test delay in the IRQ threads: a falling
edge during chip removal is read as rising; with this change, it is
dropped and read() returns -ENODEV. The HTE path was compile-tested.

Fixes: 61f922db7221 ("gpio: userspace ABI for reading GPIO line events")
Fixes: 73e0341992b6 ("gpiolib: cdev: support edge detection for uAPI v2")
Fixes: 2068339a6c35 ("gpiolib: cdev: Add hardware timestamp clock type")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20261020-gpiolib-chip-removal-v3-0-aambrozewicz@nvidia.com?part=6
Assisted-by: LLM
Signed-off-by: Adrian Ambrozewicz <aambrozewicz@nvidia.com>
---
 drivers/gpio/gpiolib-cdev.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index cf23b5296fd1..0d6853751e6e 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -643,6 +643,8 @@ static enum hte_return process_hw_ts_thread(void *p)
 		level = (line->raw_level >= 0) ?
 				line->raw_level :
 				gpiod_get_raw_value_cansleep(line->desc);
+		if (level < 0)
+			return HTE_CB_HANDLED;
 
 		if (edflags & GPIO_V2_LINE_FLAG_ACTIVE_LOW)
 			level = !level;
@@ -743,6 +745,7 @@ static irqreturn_t edge_irq_thread(int irq, void *p)
 	struct line *line = p;
 	struct linereq *lr = line->req;
 	struct gpio_v2_line_event le;
+	int level;
 
 	/* Do not leak kernel stack to userspace */
 	memset(&le, 0, sizeof(le));
@@ -763,7 +766,10 @@ static irqreturn_t edge_irq_thread(int irq, void *p)
 
 	switch (READ_ONCE(line->edflags) & GPIO_V2_LINE_EDGE_FLAGS) {
 	case GPIO_V2_LINE_FLAG_EDGE_BOTH:
-		le.id = line_event_id(gpiod_get_value_cansleep(line->desc));
+		level = gpiod_get_value_cansleep(line->desc);
+		if (level < 0)
+			return IRQ_HANDLED;
+		le.id = line_event_id(level);
 		break;
 	case GPIO_V2_LINE_FLAG_EDGE_RISING:
 		le.id = GPIO_V2_LINE_EVENT_RISING_EDGE;
@@ -2006,6 +2012,8 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p)
 	    && le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE) {
 		int level = gpiod_get_value_cansleep(le->desc);
 
+		if (level < 0)
+			return IRQ_HANDLED;
 		if (level)
 			/* Emit low-to-high event */
 			ge.id = GPIOEVENT_EVENT_RISING_EDGE;
-- 
2.43.0