Re: [PATCH v5] nvme: Skip trace complete_rq on host path error

[Keith Busch <kbusch@kernel.org>]

On Thu, Mar 26, 2026 at 03:31:24PM +0100, hch@lst.de wrote:
> On Thu, Mar 26, 2026 at 08:28:46AM -0600, Keith Busch wrote:
> > On Thu, Mar 26, 2026 at 03:51:52PM +0900, 전민식 wrote:
> > >  {
> > >  	struct nvme_ctrl *ctrl = nvme_req(req)->ctrl;
> > >  
> > > -	trace_nvme_complete_rq(req);
> > > +	/*
> > > +	 * The idea for these trace events was to match up commands
> > > +	 * dispatched to hardware with the hardware's posted response.
> > > +	 * So skip tracing for undispatched commands.
> > > +	 */
> > > +	if (nvme_req(req)->status != NVME_SC_HOST_PATH_ERROR)
> > > +		trace_nvme_complete_rq(req);
> > > +
> > 
> > Well, how do we know a controller doesnn't actually return that status
> > code? I was just suggesting to skip the trace for the condition we never
> > dispatched the command. An added bonus is we don't need a mostly
> > unnecessary 'if' check on every IO.
> 
> The 7?h error values were added for host use.  The description of
> the section in the spec suggests this, but isn't actually as clear
> as I would like it.  I wonder if we need to verify that controller
> don't incorrectly return it, as that could cause some problems?

Yeah, the spec is not very clear on their use. It just defines the codes
and a one sentence description, and then never mentioned again. I think
it allows the possibility for the controller to internally complete a
command with such status from some undefined OOB mechanism. I'm not sure
why the host needs to have their own self-generated status codes anyway
since it can already attach whatever arbitrary flags it wants to its
private data, like how we use NVME_REQ_CANCELLED.

Anyway if a controller did return it for whatever reason, even if it is
a bug, we'd want to see it in the trace.