[PATCH 1/3] nvme-core: improve avoiding false remove namespace

[Sagi Grimberg]

>> We really need to take a step back here, I really don't like how
>> we are growing implicit assumptions on how statuses are interpreted.
>>
>> Why don't we remove the -ENODEV error propagation back and instead
>> take care of it in the specific call-sites where we want to ignore
>> errors with proper quirks?
> 
> So the one thing I'm not even sure about is if just ignoring the
> errors was a good idea to start with.  They obviously are if we just
> did a rescan and did run into an error while rescanning a namespace
> that didn't change.  But what if it actually did change?

Right, we don't know, so if we failed without DNR, we assume that
we will retry again and ignore the error. The assumption is that
we will retry when we will reconnect as we don't have a retry mechanism
for these requests.

> So I think a logic like in this patch kinda makes sense, but I think
> we also need to retry and scan again on these kinds of errors.

So you are OK with keeping nvme_submit_sync_cmd returning -ENODEV for
cancelled requests and have the scan flow assume that these are
cancelled requests?

At the very least we need a good comment to say what is going on there.

   Btw,
> did you ever actually see -ENOMEM in practice?  With the small
> allocations that we do it really should not happen normally, so
> special casing for it always felt a little strange.

Never seen it, it's there just because we have allocations in the path.

> FYI, I've started rebasing various bits of work I've done to start
> untangling the mess.  Here is my current WIP, which in this form
> is completely untested:
> 
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/nvme-scanning-cleanup

This does not yet contain sorting out what is discussed here correct?