On Thu, Oct 28, 2021 at 07:36:19AM +0900, Daejun Park wrote:
> This patch addresses the issue of using the wrong API to create a
> pre_request for HPB READ.
> HPB READ candidate that require a pre-request will try to allocate a
> pre-request only during request_timeout_ms (default: 0). Otherwise, it is
Can you explain about 'only during request_timeout_ms'?
>From the following code in ufshpb_prep(), the pre-request is allocated
for each READ IO in case of (!ufshpb_is_legacy(hba) && ufshpb_is_required_wb(hpb,
transfer_len)).
if (!ufshpb_is_legacy(hba) &&
ufshpb_is_required_wb(hpb, transfer_len)) {
err = ufshpb_issue_pre_req(hpb, cmd, &read_id);
> passed as normal READ, so deadlock problem can be resolved.
>
> Signed-off-by: Daejun Park <daejun7.park@xxxxxxxxxxx>
> ---
> drivers/scsi/ufs/ufshpb.c | 11 +++++------
> drivers/scsi/ufs/ufshpb.h | 1 +
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshpb.c b/drivers/scsi/ufs/ufshpb.c
> index 02fb51ae8b25..3117bd47d762 100644
> --- a/drivers/scsi/ufs/ufshpb.c
> +++ b/drivers/scsi/ufs/ufshpb.c
> @@ -548,8 +548,7 @@ static int ufshpb_execute_pre_req(struct ufshpb_lu *hpb, struct scsi_cmnd *cmd,
> read_id);
> rq->cmd_len = scsi_command_size(rq->cmd);
>
> - if (blk_insert_cloned_request(q, req) != BLK_STS_OK)
> - return -EAGAIN;
> + blk_execute_rq_nowait(NULL, req, true, ufshpb_pre_req_compl_fn);
Be care with above change, blk_insert_cloned_request() allocates
driver tag and issues the request to LLD directly, then returns the
result. If anything fails in the code path, -EAGAIN is returned.
But blk_execute_rq_nowait() simply queued the request in block layer,
and run hw queue. It doesn't allocate driver tag, and doesn't issue it
to LLD.
So ufshpb_execute_pre_req() may think the pre-request is issued to LLD
successfully, but actually not, maybe never. What will happen after the
READ IO is issued to device, but the pre-request(write buffer) isn't
sent to device?
>
> hpb->stats.pre_req_cnt++;
>
> @@ -2315,19 +2314,19 @@ struct attribute_group ufs_sysfs_hpb_param_group = {
> static int ufshpb_pre_req_mempool_init(struct ufshpb_lu *hpb)
> {
> struct ufshpb_req *pre_req = NULL, *t;
> - int qd = hpb->sdev_ufs_lu->queue_depth / 2;
> int i;
>
> INIT_LIST_HEAD(&hpb->lh_pre_req_free);
>
> - hpb->pre_req = kcalloc(qd, sizeof(struct ufshpb_req), GFP_KERNEL);
> - hpb->throttle_pre_req = qd;
> + hpb->pre_req = kcalloc(HPB_INFLIGHT_PRE_REQ, sizeof(struct ufshpb_req),
> + GFP_KERNEL);
> + hpb->throttle_pre_req = HPB_INFLIGHT_PRE_REQ;
> hpb->num_inflight_pre_req = 0;
>
> if (!hpb->pre_req)
> goto release_mem;
>
> - for (i = 0; i < qd; i++) {
> + for (i = 0; i < HPB_INFLIGHT_PRE_REQ; i++) {
> pre_req = hpb->pre_req + i;
> INIT_LIST_HEAD(&pre_req->list_req);
> pre_req->req = NULL;
> diff --git a/drivers/scsi/ufs/ufshpb.h b/drivers/scsi/ufs/ufshpb.h
> index a79e07398970..411a6d625f53 100644
> --- a/drivers/scsi/ufs/ufshpb.h
> +++ b/drivers/scsi/ufs/ufshpb.h
> @@ -50,6 +50,7 @@
> #define HPB_RESET_REQ_RETRIES 10
> #define HPB_MAP_REQ_RETRIES 5
> #define HPB_REQUEUE_TIME_MS 0
> +#define HPB_INFLIGHT_PRE_REQ 4
Can you explain how this change solves the deadlock?
Thanks,
Ming
