[PATCH 4.20 50/80] gpiolib: fix line event timestamps for nested irqs

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>

commit 1033be58992f818dc564196ded2bcc3f360bc297 upstream.

Nested interrupts run inside the calling thread's context and the top
half handler is never called which means that we never read the
timestamp.

This issue came up when trying to read line events from a gpiochip
using regmap_irq_chip for interrupts.

Fix it by reading the timestamp from the irq thread function if it's
still 0 by the time the second handler is called.

Fixes: d58f2bf261fd ("gpio: Timestamp events in hardirq handler")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpio/gpiolib.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -828,7 +828,14 @@ static irqreturn_t lineevent_irq_thread(
 	/* Do not leak kernel stack to userspace */
 	memset(&ge, 0, sizeof(ge));
 
-	ge.timestamp = le->timestamp;
+	/*
+	 * We may be running from a nested threaded interrupt in which case
+	 * we didn't get the timestamp from lineevent_irq_handler().
+	 */
+	if (!le->timestamp)
+		ge.timestamp = ktime_get_real_ns();
+	else
+		ge.timestamp = le->timestamp;
 
 	if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE
 	    && le->eflags & GPIOEVENT_REQUEST_FALLING_EDGE) {