Re: [PATCH] nvme-multipath: set BIO_REMAPPED on bios remapped to per-path namespace disks

[Keith Busch <kbusch@kernel.org>]

On Mon, May 18, 2026 at 08:59:09PM +0000, Achkinazi, Igor wrote:
> - submit_bio_noacct_nocheck is block-internal and not exported, so using it
> from NVMe would require a block-layer API change just for this.

That is not a valid reason to not do this. We often export and unexport
APIs as needs evolve. I'm not saying you have to use this API, but I'm
just not yet seeing why we shouldn't.

> - it bypasses more checks than I see we need here (throttling, RO, crypto,
> op-type), I prefer bypassing only the EOD check.

I do not think we need any of those on the hidden device either. The
stacked limits should have caught any problems or handled any policy on
the first pass.

Though I am aware of certain limit checks that go through here are not
done under the queue's entered reference count so there's some racy
things possible, but that's a pre-existing issue and doing
submit_bio_noacct a 2nd time doesn't help.

> - BIO_REMAPPED propagates to split clones, so it covers all resubmissions,
> not just the initial one.

Submitting split clones already uses submit_bio_noacct_nocheck() so the
BIO_REMAPPED flag doesn't come into play there either.

And BIO_REMAPPED applies to when the bio's bd_part is a partition. The
multipath layer overrides the block device with the part0 of the path,
so there is no partition (and we may not have been dealing with a
partition in first place), so this patch is introducing a new implicit
expectation on what this flag means. Consider a real failover going
through the requeue_list using the submit_bio_noacct() again. If you've
already set BIO_REMAPPED, then it skips the checks, but that could have
happened across a controller format change that modified all the limits,
so you probably want the eod checks to happen again on this scenario.
Your suggestion would skip it because you're using BIO_REMAPPED as a
proxy to skip "eod" checks.