Original link : here

If you are calling a function such as wp_update_post that includes the save_post hook, your hooked function will create an infinite loop. To avoid this, unhook your function before calling the function you need, then re-hook it afterward.

<?php
// this function makes all posts in the default category private

function set_private_categories($post_id) {
	// If this is a revision, get real post ID
	if ( $parent_id = wp_is_post_revision( $post_id ) ) 
		$post_id = $parent_id;

	// Get default category ID from options
	$defaultcat = get_option( 'default_category' );

	// Check if this post is in default category
	if ( in_category( $defaultcat, $post_id ) ) {
		// unhook this function so it doesn't loop infinitely
		remove_action( 'save_post', 'set_private_categories' );

		// update the post, which calls save_post again
		wp_update_post( array( 'ID' => $post_id, 'post_status' => 'private' ) );

		// re-hook this function
		add_action( 'save_post', 'set_private_categories' );
	}
}
add_action( 'save_post', 'set_private_categories' );
?>

NOTE: It is very important to use the same parameters in remove_action than in add_action. Example with priority below (extract)… if the parameters are not the same, the infinite loop occurs…

// unhook this function so it doesn't loop infinitely
		remove_action( 'save_post', 'set_private_categories', 13, 2 );

		// update the post, which calls save_post again
		wp_update_post( array( 'ID' => $post_id, 'post_status' => 'private' ) );

		// re-hook this function
		add_action( 'save_post', 'set_private_categories', 13, 2 );
	}
}
add_action( 'save_post', 'set_private_categories', 13, 2 );