new helper: uaccess_kernel()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
index ac8bd58..0ba1430 100644
--- a/arch/parisc/include/asm/futex.h
+++ b/arch/parisc/include/asm/futex.h
@@ -109,7 +109,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	/* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is
 	 * our gateway page, and causes no end of trouble...
 	 */
-	if (segment_eq(KERNEL_DS, get_fs()) && !uaddr)
+	if (uaccess_kernel() && !uaddr)
 		return -EFAULT;
 
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))