Re: [PATCH] nvme: reject completions for requests that are not in flight

[Keith Busch <kbusch@kernel.org>]

On Wed, Nov 04, 2026 at 04:46:12PM -0300, Mauricio Faria de Oliveira wrote:
> On 2026-11-03 17:06, Keith Busch wrote:
> > On Tue, Nov 03, 2026 at 04:54:27PM -0300, Mauricio Faria de Oliveira wrote:
> >> For the former question, I'd imagine other block drivers might be
> >> subject to a similar issue, under incorrect completions, and can take a
> >> look at this later. I'd appreciate feedback on the points above before
> >> trying to address it generically in the block layer, if at all possible.
> > 
> > Here's my real concern: the proposal is a race. Another CPU can change
> > the request state to in-flight, and this code will declare it complete
> > before the hardware even saw it. It's a silent data corruption problem
> > that we can't fix because it is impossible to tell the difference
> > between a bogus and a legit completion at that point. This kind of
> > hardware shouldn't be allowed to exist as it can't be used successfully
> > when it behaves this way.
> 
> Could you please clarify? Not that I'm defending the patch; just so I
> understand your point.
> 
> The reason I ask is, IIUIC, if another CPU changes the request state to
> in-flight and wins the race over an incorrect completion that maps to
> that request, the request is declared complete anyway, even without this
> code, no?

Yes, the race I'm mentioning is pre-existing assuming we're dealing with
this kind of protocol breaking hardware. It just can't be fixed on the
kernel side, and the proposal trying to cater to it makes it painfully
obvious. I'd rather crash the kernel than risk passing on corrupted data
as a success.