Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Oleksandr Natalenko <oleksandr@natalenko.name>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     linux-kernel@vger.kernel.org, Jens Axboe <axboe@fb.com>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        linux-nvme@lists.infradead.org,
        David Jeffery <djeffery@redhat.com>,
        Laurence Oberman <loberman@redhat.com>,
        Paolo Valente <paolo.valente@linaro.org>,
        Jan Kara <jack@suse.cz>, Sasha Levin <sashal@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Keith Busch <kbusch@kernel.org>
Subject: Re: New warning in nvme_setup_discard
Date:   Fri, 16 Jul 2021 07:53:28 +0200
Message-ID: <81322754.HEIg0oD171@natalenko.name>
In-Reply-To: <YPDr8ucoDCE4NBSe@T590>
References: <4729812.CpyZKHjjVO@natalenko.name> <YPDr8ucoDCE4NBSe@T590>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hello.

On p=C3=A1tek 16. =C4=8Dervence 2021 4:16:18 CEST Ming Lei wrote:
> >  850     if (WARN_ON_ONCE(n !=3D segments)) {
>=20
> What is 'n' and 'segments'?

So, I used this change to check that:

```
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 66973bb56305..0a64f2f77daf 100644
=2D-- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -847,7 +847,8 @@ static blk_status_t nvme_setup_discard(struct nvme_ns *=
ns,=20
struct request *req,
 		n++;
 	}
=20
=2D	if (WARN_ON_ONCE(n !=3D segments)) {
+	if (unlikely(n !=3D segments)) {
+		pr_warn("nvme_setup_discard: n !=3D segments (%u !=3D %u)\n", n,=20
segments);
 		if (virt_to_page(range) =3D=3D ns->ctrl->discard_page)
 			clear_bit_unlock(0, &ns->ctrl->discard_page_busy);
 		else

```

and the result is:

```
nvme_setup_discard: n !=3D segments (3 !=3D 2)
nvme_setup_discard: n !=3D segments (12 !=3D 11)
```

(those are from different boots)

Thanks.

=2D-=20
Oleksandr Natalenko (post-factum)