Re: [PATCH v2 11/11] Partially revert "hw/block/nvme: drain namespaces on sq deletion"

[Keith Busch]

On Thu, Jun 17, 2021 at 09:06:57PM +0200, Klaus Jensen wrote:
> From: Klaus Jensen <k.jensen@samsung.com>
> 
> This partially reverts commit 98f84f5a4eca5c03e32fff20f246d9b4b96d6422.
> 
> Since all "multi aio" commands are now reimplemented to properly track
> the nested aiocbs, we can revert the "hack" that was introduced to make
> sure all requests we're properly drained upon sq deletion.
> 
> The revert is partial since we keep the assert that no outstanding
> requests remain on the submission queue after the explicit cancellation.
> 
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> ---
>  hw/nvme/ctrl.c | 19 ++-----------------
>  1 file changed, 2 insertions(+), 17 deletions(-)
> 
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index ec8ddb76cd39..5a1d25265a9d 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -3918,7 +3918,6 @@ static uint16_t nvme_del_sq(NvmeCtrl *n, NvmeRequest 
> *req)
>      NvmeSQueue *sq;
>      NvmeCQueue *cq;
>      uint16_t qid = le16_to_cpu(c->qid);
> -    uint32_t nsid;
>  
>      if (unlikely(!qid || nvme_check_sqid(n, qid))) {
>          trace_pci_nvme_err_invalid_del_sq(qid);
> @@ -3930,22 +3929,8 @@ static uint16_t nvme_del_sq(NvmeCtrl *n, NvmeRequest 
> *req)
>      sq = n->sq[qid];
>      while (!QTAILQ_EMPTY(&sq->out_req_list)) {
>          r = QTAILQ_FIRST(&sq->out_req_list);
> -        if (r->aiocb) {
> -            blk_aio_cancel(r->aiocb);
> -        }
> -    }
> -
> -    /*
> -     * Drain all namespaces if there are still outstanding requests that we
> -     * could not cancel explicitly.
> -     */
> -    if (!QTAILQ_EMPTY(&sq->out_req_list)) {

Quick question: was this 'if' ever even possible to hit? The preceding
'while' loop doesn't break out until the queue is empty, so this should
have been unreachable.

> -        for (nsid = 1; nsid <= NVME_MAX_NAMESPACES; nsid++) {
> -            NvmeNamespace *ns = nvme_ns(n, nsid);
> -            if (ns) {
> -                nvme_ns_drain(ns);
> -            }
> -        }
> +        assert(r->aiocb);
> +        blk_aio_cancel(r->aiocb);
>      }
>  
>      assert(QTAILQ_EMPTY(&sq->out_req_list));
> --