sys_swapon: call swap_cgroup_swapon() earlier

The call to swap_cgroup_swapon is in the middle of loading the swap map
and extents. As it only does memory allocation and does not depend on
the swapfile layout (map/extents), it can be called earlier (or later).

Move it to just after the allocation of swap_map, since it is
conceptually similar (allocates a map).
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: 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

@@ -2074,6 +2074,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		goto bad_swap;
 	}
 
+	error = swap_cgroup_swapon(p->type, maxpages);
+	if (error)
+		goto bad_swap;
+
 	nr_good_pages = maxpages - 1;	/* omit header page */
 
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
@@ -2088,10 +2092,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		}
 	}
 
-	error = swap_cgroup_swapon(p->type, maxpages);
-	if (error)
-		goto bad_swap;
-
 	if (nr_good_pages) {
 		swap_map[0] = SWAP_MAP_BAD;
 		p->max = maxpages;