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Date: Thu, 7 May 2026 07:48:09 +0200
From: Christoph Hellwig <hch@lst.de>
To: Chao Shi <coshi036@gmail.com>
Cc: linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, hch@lst.de,
	kbusch@kernel.org, sagi@grimberg.me, axboe@kernel.dk,
	Sungwoo Kim <iam@sung-woo.kim>, Dave Tian <daveti@purdue.edu>,
	Weidong Zhu <weizhu@fiu.edu>
Subject: Re: [PATCH RFC 1/2] nvme: downgrade WARN in nvme_setup_rw to
 pr_debug
Message-ID: <20260507054809.GA19796@lst.de>
References: <20260427003457.1264511-1-coshi036@gmail.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

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.