Re: [PATCH 4/5] nvme: Fail dead namespace's entered requests

[Keith Busch <keith.busch@intel.com>]

On Fri, Mar 08, 2019 at 01:54:06PM -0800, Bart Van Assche wrote:
> On Fri, 2019-03-08 at 11:19 -0700, Keith Busch wrote:
> > On Fri, Mar 08, 2019 at 10:15:27AM -0800, Bart Van Assche wrote:
> > > On Fri, 2019-03-08 at 10:40 -0700, Keith Busch wrote:
> > > > End the entered requests on a quieced queue directly rather than flush
> > > > them through the low level driver's queue_rq().
> > > > 
> > > > Signed-off-by: Keith Busch <keith.busch@intel.com>
> > > > ---
> > > >  drivers/nvme/host/core.c | 10 ++++++++--
> > > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> > > > index cc5d9a83d5af..7095406bb293 100644
> > > > --- a/drivers/nvme/host/core.c
> > > > +++ b/drivers/nvme/host/core.c
> > > > @@ -94,6 +94,13 @@ static void nvme_put_subsystem(struct nvme_subsystem *subsys);
> > > >  static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl,
> > > >  					   unsigned nsid);
> > > >  
> > > > +static bool nvme_fail_request(struct blk_mq_hw_ctx *hctx, struct request *req,
> > > > +			      void *data, bool reserved)
> > > > +{
> > > > +	blk_mq_end_request(req, BLK_STS_IOERR);
> > > > +	return true;
> > > > +}
> > > 
> > > Calling blk_mq_end_request() from outside the .queue_rq() or .complete()
> > > callback functions is wrong. Did you perhaps want to call
> > > blk_mq_complete_request()?
> > 
> > This callback can only see requests in MQ_RQ_IDLE state, and
> > bkl_mq_end_request() is the correct way to end those that never entered
> > a driver's queue_rq().
> 
> Hi Keith,
> 
> What guarantees that nvme_fail_request() only sees requests in the idle state?
> From block/blk-mq-tag.c:
> 
> /**
>  * blk_mq_queue_tag_busy_iter - iterate over all requests with a driver tag
>  * [ ... ]
>  */

It's the driver's responsibility to ensure the queue is quiesced before
requesting the iteration. When we call it through nvme_kill_queues(),
the queues were already quiesced before calling that. The only other
place it's called is on a frozen queue, so it's actually a no-op there
since there no requests once frozen.