[PATCH RFC 1/2] nvme: downgrade WARN in nvme_setup_rw to pr_debug

[Christoph Hellwig]

On Sun, Apr 26, 2026 at 08:34:56PM -0400, Chao Shi wrote:
> When an NVMe namespace is configured with embedded metadata (flbas bit 4
> set, NVME_NS_FLBAS_META_EXT) but no Protection Information (dps=0) and
> no NVME_NS_METADATA_SUPPORTED, nvme_setup_rw() fires WARN_ON_ONCE on
> any request that reaches it with REQ_INTEGRITY unset.  The WARN was
> observed repeatedly during NVMe fuzz testing with a FEMU-based fuzzer
> that performs semantic mutation of Identify Namespace responses.

What is "semantic mutation of Identify Namespace responses" supposed to
mean?

> In both cases the bio was submitted without REQ_INTEGRITY (because
> blk_get_integrity() returned NULL at dispatch time, so
> bio_integrity_action() returned 0 and bio_integrity_prep() was not
> called), and it reaches nvme_setup_rw() for a namespace where
> head->ms != 0.  The existing BLK_STS_NOTSUPP return correctly handles
> this dispatch; the WARN_ON_ONCE is a false positive.

That means we fail to properaly freeze and quiesce the queue over
updateѕm which has much worse results than just a WARN_ON.  So if we
care about this rather theoretical case we'll need to fix that.