[PATCH] probe_kernel_address() needs to do set_fs()

probe_kernel_address() purports to be generic, only it forgot to select
KERNEL_DS, so it presently won't work right on all architectures.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/uaccess.h

@@ -65,14 +65,22 @@ static inline unsigned long __copy_from_user_nocache(void *to,
  * do_page_fault() doesn't attempt to take mmap_sem.  This makes
  * probe_kernel_address() suitable for use within regions where the caller
  * already holds mmap_sem, or other locks which nest inside mmap_sem.
+ * This must be a macro because __get_user() needs to know the types of the
+ * args.
+ *
+ * We don't include enough header files to be able to do the set_fs().  We
+ * require that the probe_kernel_address() caller will do that.
  */
 #define probe_kernel_address(addr, retval)		\
 	({						\
 		long ret;				\
+		mm_segment_t old_fs = get_fs();		\
 							\
+		set_fs(KERNEL_DS);			\
 		pagefault_disable();			\
 		ret = __get_user(retval, addr);		\
 		pagefault_enable();			\
+		set_fs(old_fs);				\
 		ret;					\
 	})