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Commit bd912ef3 authored by Dongli Zhang's avatar Dongli Zhang Committed by Konrad Rzeszutek Wilk
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xen/blkfront: always allocate grants first from per-queue persistent grants 



This patch partially reverts 3df0e505 ("xen/blkfront: pseudo support for
multi hardware queues/rings"). The xen-blkfront queue/ring might hang due
to grants allocation failure in the situation when gnttab_free_head is
almost empty while many persistent grants are reserved for this queue/ring.

As persistent grants management was per-queue since 73716df7 ("xen/blkfront:
make persistent grants pool per-queue"), we should always allocate from
persistent grants first.

Acked-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: default avatarDongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 4b422cb9

drivers/block/xen-blkfront.c

+11 −8
Original line number Diff line number Diff line
@@ -708,6 +708,7 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri 
	 * existing persistent grants, or if we have to get new grants,

	 * as there are not sufficiently many free.

	 */

	bool new_persistent_gnts = false;

	struct scatterlist *sg;

	int num_sg, max_grefs, num_grant;
@@ -719,19 +720,21 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri 
		 */

		max_grefs += INDIRECT_GREFS(max_grefs);



	/*

	 * We have to reserve 'max_grefs' grants because persistent

	 * grants are shared by all rings.

	 */

	if (max_grefs > 0)

		if (gnttab_alloc_grant_references(max_grefs, &setup.gref_head) < 0) {

	/* Check if we have enough persistent grants to allocate a requests */

	if (rinfo->persistent_gnts_c < max_grefs) {

		new_persistent_gnts = true;



		if (gnttab_alloc_grant_references(

		    max_grefs - rinfo->persistent_gnts_c,

		    &setup.gref_head) < 0) {

			gnttab_request_free_callback(

				&rinfo->callback,

				blkif_restart_queue_callback,

				rinfo,

				max_grefs);

				max_grefs - rinfo->persistent_gnts_c);

			return 1;

		}

	}



	/* Fill out a communications ring structure. */

	id = blkif_ring_get_request(rinfo, req, &ring_req);
@@ -832,7 +835,7 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri 
	if (unlikely(require_extra_req))

		rinfo->shadow[extra_id].req = *extra_ring_req;



	if (max_grefs > 0)

	if (new_persistent_gnts)

		gnttab_free_grant_references(setup.gref_head);



	return 0;