xfs: fix double free of inode

If we fail to initialise the VFS inode in inode_init_always(),
it will call ->delete_inode internally resulting in the inode being
freed. Hence we need to delay the call to inode_init_always()
until after the XFS inode is sufficient set up to handle a
call to ->delete_inode, and then if that fails do not touch
the inode again at all as it has been freed.

Signed-off-by: Dave Chinner <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>

fs/xfs/xfs_iget.c

···
 	ASSERT(!spin_is_locked(&ip->i_flags_lock));
 	ASSERT(completion_done(&ip->i_flush));
 
-	/*
-	 * initialise the VFS inode here to get failures
-	 * out of the way early.
-	 */
-	if (!inode_init_always(mp->m_super, VFS_I(ip))) {
-		kmem_zone_free(xfs_inode_zone, ip);
-		return NULL;
-	}
-
 	/* initialise the xfs inode */
 	ip->i_ino = ino;
 	ip->i_mount = mp;
···
 #ifdef XFS_DIR2_TRACE
 	ip->i_dir_trace = ktrace_alloc(XFS_DIR2_KTRACE_SIZE, KM_NOFS);
 #endif
+	/*
+	* Now initialise the VFS inode. We do this after the xfs_inode
+	* initialisation as internal failures will result in ->destroy_inode
+	* being called and that will pass down through the reclaim path and
+	* free the XFS inode. This path requires the XFS inode to already be
+	* initialised. Hence if this call fails, the xfs_inode has already
+	* been freed and we should not reference it at all in the error
+	* handling.
+	*/
+	if (!inode_init_always(mp->m_super, VFS_I(ip)))
+		return NULL;
+
+	/* prevent anyone from using this yet */
+	VFS_I(ip)->i_state = I_NEW|I_LOCK;
 
 	return ip;
 }