Re: [PATCH 12/14] xen-blkback: safely unmap grants in case they are still in use

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

>   
> +static void xen_blkbk_unmap_and_respond_callback(int result, struct gntab_unmap_queue_data *data)
> +{
> +	struct pending_req* pending_req = (struct pending_req*) (data->data);
> +	struct xen_blkif *blkif = pending_req->blkif;
> +
> +	/* BUG_ON used to reproduce existing behaviour,
> +	   but is this the best way to deal with this? */
> +	BUG_ON(result);
> +	/* free page after unmap */
> +	put_free_pages(blkif, data->pages, data->count);
> +
> +	/* respond */
> +	make_response(blkif, pending_req->id,
> +		      pending_req->operation, pending_req->status);
> +	free_req(blkif, pending_req);
> +	/*
> +	 * Make sure the request is freed before releasing blkif,
> +	 * or there could be a race between free_req and the
> +	 * cleanup done in xen_blkif_free during shutdown.
> +	 *
> +	 * NB: The fact that we might try to wake up pending_free_wq
> +	 * before drain_complete (in case there's a drain going on)
> +	 * it's not a problem with our current implementation
> +	 * because we can assure there's no thread waiting on
> +	 * pending_free_wq if there's a drain going on, but it has
> +	 * to be taken into account if the current model is changed.
> +	 */
> +	if (atomic_dec_and_test(&blkif->inflight) && atomic_read(&blkif->drain)) {
> +		complete(&blkif->drain_complete);
> +	}
> +	xen_blkif_put(blkif);
> +}
> +
> +static void xen_blkbk_unmap_populate(struct pending_req *req)
> +{
> +
> +       struct gntab_unmap_queue_data* work = &req->gnttab_unmap_data;
> +       struct xen_blkif *blkif = req->blkif;
> +       struct grant_page **pages = req->segments;
> +       unsigned int i, invcount = 0;
> +
> +       for (i = 0; i < req->nr_pages; i++) {
> +		if (pages[i]->persistent_gnt != NULL) {
> +			put_persistent_gnt(blkif, pages[i]->persistent_gnt);
> +			continue;
> +		}
> +		if (pages[i]->handle == BLKBACK_INVALID_HANDLE)
> +			continue;
> +
> +		req->unmap_pages[invcount] = pages[i]->page;
> +		gnttab_set_unmap_op(&req->unmap[invcount], vaddr(pages[invcount]->page),
> +				    GNTMAP_host_map, pages[i]->handle);
> +		pages[i]->handle = BLKBACK_INVALID_HANDLE;
> +		invcount++;
> +       }
> +
> +       work->data = req;
> +       work->done = &xen_blkbk_unmap_and_respond_callback;
> +       work->unmap_ops = req->unmap;
> +       work->kunmap_ops = NULL;
> +       work->pages = req->unmap_pages;
> +       work->count = invcount;
> +
> +}
> +
> +static void xen_blkbk_unmap_and_respond(struct pending_req *req)
> +{
> +       xen_blkbk_unmap_populate(req);
> +       gnttab_unmap_refs_async(&req->gnttab_unmap_data);
> +}

(One more for this patch)

If you are using async unmap here, I thought new interface requires you 
to wait for completion (which should be called from 
xen_blkbk_unmap_and_respond_callback()).

-boris

>   /*
>    * Unmap the grant references, and also remove the M2P over-rides
>    * used in the 'pending_req'.
> @@ -982,6 +1075,9 @@ static void __end_block_io_op(struct pending_req *pending_req, int error)
>   	 * the grant references associated with 'request' and provide
>   	 * the proper response on the ring.
>   	 */
> +	if (atomic_dec_and_test(&pending_req->pendcnt))
> +		xen_blkbk_unmap_and_respond(pending_req);
> +
>   	if (atomic_dec_and_test(&pending_req->pendcnt)) {
>   		struct xen_blkif *blkif = pending_req->blkif;
>