[PATCH RESEND] gpiolib: hold gpio devices lock until ->descs array is initialised

[Dan Callaghan <dan.callaghan@xxxxxxxxxxxx>]

If a driver consuming the GPIO chip is being probed at the same time as
the GPIO driver is registering the chip, it is possible for the
consuming driver to see the ->descs array in an uninitialised state.
For example, the gpio-keys-polled driver can fail like this:

    kernel: gpiod_request: invalid GPIO (no device)
    kernel: gpio-keys-polled PRP0001:07: failed to get gpio: -22
    kernel: gpio-keys-polled: probe of PRP0001:07 failed with error -22

This patch makes gpiochip_add() hold the lock protecting gpio_devices
until it has finished setting desc->gdev on the newly inserted list
entry.

Signed-off-by: Dan Callaghan <dan.callaghan@xxxxxxxxxxxx>
---
Resending this one because I failed to cc the maintainers on the 
original posting, sorry about that.

 drivers/gpio/gpiolib.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 78a16e42f222..33c72fb12bb5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1495,11 +1495,11 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data,
 		goto err_free_label;
 	}
 
-	spin_unlock_irqrestore(&gpio_lock, flags);
-
 	for (i = 0; i < chip->ngpio; i++)
 		gdev->descs[i].gdev = gdev;
 
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
 #ifdef CONFIG_PINCTRL
 	INIT_LIST_HEAD(&gdev->pin_ranges);
 #endif
-- 
2.21.0