kfifo: fix kfifo_alloc() to return a signed int value

Add a new __kfifo_int_must_check_helper() helper function, which is needed
for kfifo_alloc() to return the right signed integer value.

The origin __kfifo_must_check_helper() helper was renamed into
__kfifo_uint_must_check_helper() to show the sign which is expected and
returned.

(And revert the temporary disabling of __kfifo_must_check_helper())

Signed-off-by: Stefani Seibold <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kfifo.h

···
 	}
 
 
-/* __kfifo_must_check_helper() is temporarily disabled because it was faulty */
-#define __kfifo_must_check_helper(x) (x)
+static inline unsigned int __must_check
+__kfifo_uint_must_check_helper(unsigned int val)
+{
+	return val;
+}
+
+static inline int __must_check
+__kfifo_int_must_check_helper(int val)
+{
+	return val;
+}
 
 /**
  * kfifo_initialized - Check if the fifo is initialized
···
  * @fifo: address of the fifo to be used
  */
 #define	kfifo_avail(fifo) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmpq = (fifo); \
 	const size_t __recsize = sizeof(*__tmpq->rectype); \
···
  * This function returns the size of the next fifo record in number of bytes.
  */
 #define kfifo_peek_len(fifo) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	const size_t __recsize = sizeof(*__tmp->rectype); \
···
  * Return 0 if no error, otherwise an error code.
  */
 #define kfifo_alloc(fifo, size, gfp_mask) \
-__kfifo_must_check_helper( \
+__kfifo_int_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	struct __kfifo *__kfifo = &__tmp->kfifo; \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_get(fifo, val) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	typeof((val) + 1) __val = (val); \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_peek(fifo, val) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	typeof((val) + 1) __val = (val); \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_out(fifo, buf, n) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	typeof((buf) + 1) __buf = (buf); \
···
  * copied.
  */
 #define	kfifo_out_spinlocked(fifo, buf, n, lock) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	unsigned long __flags; \
 	unsigned int __ret; \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_from_user(fifo, from, len, copied) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	const void __user *__from = (from); \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_to_user(fifo, to, len, copied) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	void __user *__to = (to); \
···
  * writer, you don't need extra locking to use these macro.
  */
 #define	kfifo_out_peek(fifo, buf, n) \
-__kfifo_must_check_helper( \
+__kfifo_uint_must_check_helper( \
 ({ \
 	typeof((fifo) + 1) __tmp = (fifo); \
 	typeof((buf) + 1) __buf = (buf); \