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xen/blkfront: always allocate grants first from per-queue persistent grants

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This patch partially reverts 3df0e50 ("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 73716df ("xen/blkfront:
make persistent grants pool per-queue"), we should always allocate from
persistent grants first.

Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Dongli Zhang 2017-06-28 20:57:28 +08:00 committed by Konrad Rzeszutek Wilk
parent 4b422cb998
commit bd912ef3e4
1 changed files with 11 additions and 8 deletions
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19
drivers/block/xen-blkfront.c
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@ -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;