linux-kernel - Re: New warning in nvme_setup

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Message-ID: <81322754.HEIg0oD171@natalenko.name>
Date:   Fri, 16 Jul 2021 07:53:28 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org,
        David Jeffery <djeffery@...hat.com>,
        Laurence Oberman <loberman@...hat.com>,
        Paolo Valente <paolo.valente@...aro.org>,
        Jan Kara <jack@...e.cz>, Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Keith Busch <kbusch@...nel.org>
Subject: Re: New warning in nvme_setup_discard

Hello.

On pátek 16. července 2021 4:16:18 CEST Ming Lei wrote:
> >  850     if (WARN_ON_ONCE(n != segments)) {
> 
> 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
--- 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, 
struct request *req,
 		n++;
 	}
 
-	if (WARN_ON_ONCE(n != segments)) {
+	if (unlikely(n != segments)) {
+		pr_warn("nvme_setup_discard: n != segments (%u != %u)\n", n, 
segments);
 		if (virt_to_page(range) == ns->ctrl->discard_page)
 			clear_bit_unlock(0, &ns->ctrl->discard_page_busy);
 		else

```

and the result is:

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

(those are from different boots)

Thanks.

-- 
Oleksandr Natalenko (post-factum)