| Message ID | 1498624983-6293-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Jun 28, 2017 at 12:43:03PM +0800, Dongli Zhang wrote: > 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 <dongli.zhang@oracle.com> > --- > drivers/block/xen-blkfront.c | 17 ++++++++++------- > 1 file changed, 10 insertions(+), 7 deletions(-) > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c > index 3945963..d2b759f 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; > > @@ -724,12 +725,13 @@ 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, AFAICT you should also change the call to gnttab_request_free_callback to request for max_grefs - rinfo->persistent_gnts_c. In any case the number of persistent grants is not going to decrease now, because the buffer is per-queue, so the only thing that can happen is that requests complete and the number of persistent grants increase. Roger.
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 3945963..d2b759f 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; @@ -724,12 +725,13 @@ 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, @@ -737,6 +739,7 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri max_grefs); return 1; } + } /* Fill out a communications ring structure. */ id = blkif_ring_get_request(rinfo, req, &ring_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;
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 <dongli.zhang@oracle.com> --- drivers/block/xen-blkfront.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)