gpio_free might sleep, generic part

According to the documentation gpio_free should only be called from task
context only.  To make this more explicit add a might sleep to all
implementations.

This is the generic part which changes gpiolib and the fallback
implementation only.

Signed-off-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 8d29405..317004f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -792,6 +792,8 @@
 	unsigned long		flags;
 	struct gpio_desc	*desc;
 
+	might_sleep();
+
 	if (!gpio_is_valid(gpio)) {
 		WARN_ON(extra_checks);
 		return;