sys_swapon: move setting of swapfilepages near use

There is no reason I can see to read inode->i_size long before it is
needed. Move its read to just before it is needed, to reduce the
variable lifetime.
Signed-off-by: NCesar Eduardo Barros <cesarb@cesarb.net>
Tested-by: NEric B Munson <emunson@mgebm.net>
Acked-by: NEric B Munson <emunson@mgebm.net>
Reviewed-by: NJesper Juhl <jj@chaosbits.net>
Reviewed-by: NPekka Enberg <penberg@kernel.org>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -1975,8 +1975,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (unlikely(error))
 		goto bad_swap;
 
-	swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
-
 	/*
 	 * Read the swap header.
 	 */
@@ -2045,6 +2043,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	error = -EINVAL;
 	if (!maxpages)
 		goto bad_swap;
+	swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
 	if (swapfilepages && maxpages > swapfilepages) {
 		printk(KERN_WARNING
 		       "Swap area shorter than signature indicates\n");