btrfs: fix warning in iput for bad-inode

iput() shouldn't be called for inodes in I_NEW state.
We need to mark inode as constructed first.

WARNING: at fs/inode.c:1309 iput+0x20b/0x210()
Call Trace:
[<ffffffff8103e7ba>] warn_slowpath_common+0x7a/0xb0
[<ffffffff8103e805>] warn_slowpath_null+0x15/0x20
[<ffffffff810eaf0b>] iput+0x20b/0x210
[<ffffffff811b96fb>] btrfs_iget+0x1eb/0x4a0
[<ffffffff811c3ad6>] btrfs_run_defrag_inodes+0x136/0x210
[<ffffffff811ad55f>] cleaner_kthread+0x17f/0x1a0
[<ffffffff81035b7d>] ? sub_preempt_count+0x9d/0xd0
[<ffffffff811ad3e0>] ? transaction_kthread+0x280/0x280
[<ffffffff8105af86>] kthread+0x96/0xa0
[<ffffffff814336d4>] kernel_thread_helper+0x4/0x10
[<ffffffff8105aef0>] ? kthread_worker_fn+0x190/0x190
[<ffffffff814336d0>] ? gs_change+0xb/0xb

Signed-off-by: Sergei Trofimovich <[e-mail]>
CC: Konstantin Khlebnikov <[e-mail]>
Tested-by: David Sterba <[e-mail]>
CC: Josef Bacik <[e-mail]>
CC: Chris Mason <[e-mail]>
Signed-off-by: Chris Mason <[e-mail]>

fs/btrfs/inode.c

···
 			 struct btrfs_root *root, int *new)
 {
 	struct inode *inode;
-	int bad_inode = 0;
 
 	inode = btrfs_iget_locked(s, location->objectid, root);
 	if (!inode)
···
 			if (new)
 				*new = 1;
 		} else {
-			bad_inode = 1;
+			unlock_new_inode(inode);
+			iput(inode);
+			inode = ERR_PTR(-ESTALE);
 		}
-	}
-
-	if (bad_inode) {
-		iput(inode);
-		inode = ERR_PTR(-ESTALE);
 	}
 
 	return inode;