Re: [PATCH] hw/block/nvme: drain namespaces on sq deletion

[Klaus Jensen <its@irrelevant.dk>]

[-- Attachment #1: Type: text/plain, Size: 3086 bytes --]

On Feb 11 11:49, Minwoo Im wrote:
> On 21-01-27 14:15:05, Klaus Jensen wrote:
> > From: Klaus Jensen <k.jensen@samsung.com>
> > 
> > For most commands, when issuing an AIO, the BlockAIOCB is stored in the
> > NvmeRequest aiocb pointer when the AIO is issued. The purpose of storing
> > this is to allow the AIO to be cancelled when deleting submission
> > queues (it is currently not used for Abort).
> > 
> > Since the addition of the Dataset Management command and Zoned
> > Namespaces, NvmeRequests may involve more than one AIO and the AIOs are
> > issued without saving a reference to the BlockAIOCB. This is a problem
> > since nvme_del_sq will attempt to cancel outstanding AIOs, potentially
> > with an invalid BlockAIOCB.
> > 
> > Fix this by instead of explicitly cancelling the requests, just allow
> > the AIOs to complete by draining the namespace blockdevs.
> > 
> > Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> > ---
> >  hw/block/nvme.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> > 
> > diff --git a/hw/block/nvme.c b/hw/block/nvme.c
> > index 316858fd8adf..91f6fb6da1e2 100644
> > --- a/hw/block/nvme.c
> > +++ b/hw/block/nvme.c
> > @@ -403,6 +403,7 @@ static void nvme_req_clear(NvmeRequest *req)
> >  {
> >      req->ns = NULL;
> >      req->opaque = NULL;
> > +    req->aiocb = NULL;
> >      memset(&req->cqe, 0x0, sizeof(req->cqe));
> >      req->status = NVME_SUCCESS;
> >  }
> > @@ -2396,6 +2397,7 @@ static uint16_t nvme_del_sq(NvmeCtrl *n, NvmeRequest *req)
> >      NvmeSQueue *sq;
> >      NvmeCQueue *cq;
> >      uint16_t qid = le16_to_cpu(c->qid);
> > +    int i;
> >  
> >      if (unlikely(!qid || nvme_check_sqid(n, qid))) {
> >          trace_pci_nvme_err_invalid_del_sq(qid);
> > @@ -2404,12 +2406,18 @@ static uint16_t nvme_del_sq(NvmeCtrl *n, NvmeRequest *req)
> >  
> >      trace_pci_nvme_del_sq(qid);
> >  
> > -    sq = n->sq[qid];
> > -    while (!QTAILQ_EMPTY(&sq->out_req_list)) {
> > -        r = QTAILQ_FIRST(&sq->out_req_list);
> > -        assert(r->aiocb);
> > -        blk_aio_cancel(r->aiocb);
> > +    for (i = 1; i <= n->num_namespaces; i++) {
> > +        NvmeNamespace *ns = nvme_ns(n, i);
> > +        if (!ns) {
> > +            continue;
> > +        }
> > +
> > +        nvme_ns_drain(ns);
> 
> If we just drain the entire namespaces here, commands which has nothing
> to do with the target sq to be deleted will be drained.  And this might
> be a burden for a single SQ deletion.
> 

That is true. But how often would you dynamically delete and create I/O
submission queues in the fast path?

> By the way, agree with the multiple AIOs references problem for newly added
> commands.  But, shouldn't we manage the inflight AIO request references for
> the newlly added commands with some other way and kill them all
> explicitly as it was?  Maybe some of list for AIOCBs?

I was hesitant to add more stuff to NvmeRequest (like a QTAILQ to track
this). Getting a steady-state with draining was an easy fix.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]