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.
Signed-off-by: Dongli Zhang
---
Changed since v1:
* use "max_grefs - rinfo->persistent_gnts_c" as callback argument
---
drivers/block/xen-blkfront.c | 19 +++
1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 3945963..4544a1c 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -713,6 +713,7 @@ 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;
@@ -724,19 +725,21 @@ 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, _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,
+ _head) < 0) {
gnttab_request_free_callback(
>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, _req);
@@ -837,7 +840,7 @@ 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;
--
2.7.4
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