vfs: fix inode_init_always calling convention

Currently inode_init_always calls into ->destroy_inode if the additional
initialization fails.  That's not only counter-intuitive because
inode_init_always did not allocate the inode structure, but in case of
XFS it's actively harmful as ->destroy_inode might delete the inode from
a radix-tree that has never been added.  This in turn might end up
deleting the inode for the same inum that has been instanciated by
another process and cause lots of cause subtile problems.

Also in the case of re-initializing a reclaimable inode in XFS it would
free an inode we still want to keep alive.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>

fs/inode.c

@@ -120,12 +120,11 @@ static void wake_up_inode(struct inode *inode)
  * These are initializations that need to be done on every inode
  * allocation as the fields are not initialised by slab allocation.
  */
-struct inode *inode_init_always(struct super_block *sb, struct inode *inode)
+int inode_init_always(struct super_block *sb, struct inode *inode)
 {
 	static const struct address_space_operations empty_aops;
 	static struct inode_operations empty_iops;
 	static const struct file_operations empty_fops;
-
 	struct address_space *const mapping = &inode->i_data;
 
 	inode->i_sb = sb;
@@ -152,7 +151,7 @@ struct inode *inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->dirtied_when = 0;
 
 	if (security_inode_alloc(inode))
-		goto out_free_inode;
+		goto out;
 
 	/* allocate and initialize an i_integrity */
 	if (ima_inode_alloc(inode))
@@ -198,16 +197,12 @@ struct inode *inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->i_fsnotify_mask = 0;
 #endif
 
-	return inode;
+	return 0;
 
 out_free_security:
 	security_inode_free(inode);
-out_free_inode:
-	if (inode->i_sb->s_op->destroy_inode)
-		inode->i_sb->s_op->destroy_inode(inode);
-	else
-		kmem_cache_free(inode_cachep, (inode));
-	return NULL;
+out:
+	return -ENOMEM;
 }
 EXPORT_SYMBOL(inode_init_always);
 
@@ -220,9 +215,18 @@ static struct inode *alloc_inode(struct super_block *sb)
 	else
 		inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL);
 
-	if (inode)
-		return inode_init_always(sb, inode);
-	return NULL;
+	if (!inode)
+		return NULL;
+
+	if (unlikely(inode_init_always(sb, inode))) {
+		if (inode->i_sb->s_op->destroy_inode)
+			inode->i_sb->s_op->destroy_inode(inode);
+		else
+			kmem_cache_free(inode_cachep, inode);
+		return NULL;
+	}
+
+	return inode;
 }
 
 void destroy_inode(struct inode *inode)