sys_swapon: use a single error label

sys_swapon currently has two error labels, bad_swap and bad_swap_2.
bad_swap does the same as bad_swap_2 plus destroy_swap_extents() and
swap_cgroup_swapoff(); both are noops in the places where bad_swap_2 is
jumped to. With a single extra test for inode (matching the one in the
S_ISREG case below), all the error paths in the function can go to
bad_swap.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Tested-by: Eric B Munson <emunson@mgebm.net>
Acked-by: Eric B Munson <emunson@mgebm.net>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swapfile.c

@@ -1918,13 +1918,13 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (IS_ERR(name)) {
 		error = PTR_ERR(name);
 		name = NULL;
-		goto bad_swap_2;
+		goto bad_swap;
 	}
 	swap_file = filp_open(name, O_RDWR|O_LARGEFILE, 0);
 	if (IS_ERR(swap_file)) {
 		error = PTR_ERR(swap_file);
 		swap_file = NULL;
-		goto bad_swap_2;
+		goto bad_swap;
 	}
 
 	p->swap_file = swap_file;
@@ -2141,13 +2141,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	error = 0;
 	goto out;
 bad_swap:
-	if (S_ISBLK(inode->i_mode) && p->bdev) {
+	if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
 		set_blocksize(p->bdev, p->old_block_size);
 		blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
 	}
 	destroy_swap_extents(p);
 	swap_cgroup_swapoff(p->type);
-bad_swap_2:
 	spin_lock(&swap_lock);
 	p->swap_file = NULL;
 	p->flags = 0;