linux-kernel - Re: [PATCH V6 09/10] cxl/mem: Retry reading CDAT on failure

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Message-ID: <20220201185928.ffdgvnn6mcmo7by7@intel.com>
Date:   Tue, 1 Feb 2022 10:59:28 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     ira.weiny@...el.com
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH V6 09/10] cxl/mem: Retry reading CDAT on failure

On 22-01-31 23:19:51, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> The CDAT read may fail for a number of reasons but mainly it is possible
> to get different parts of a valid state.  The checksum in the CDAT table
> protects against this.
> 
> Now that the checksum is validated issue a retry if the CDAT read fails.
> For now 2 retries are implemented.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> NOTE: Is 2 enough?  Should this just be delayed until the time when the
> data is actually needed and not there?

I can't speak to retries at all, but one small issue below. It might make sense
if we keep this to make it a modparam.

> 
> Changes from V5:
> 	New patch -- easy to push off or drop.
> ---
>  drivers/cxl/core/memdev.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index a01068e98333..11d721c56f08 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -356,7 +356,8 @@ static const struct file_operations cxl_memdev_fops = {
>  	.llseek = noop_llseek,
>  };
>  
> -static int read_cdat_data(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
> +static int __read_cdat_data(struct cxl_memdev *cxlmd,
> +			    struct cxl_dev_state *cxlds)
>  {
>  	struct device *dev = &cxlmd->dev;
>  	size_t cdat_length;
> @@ -371,6 +372,20 @@ static int read_cdat_data(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
>  	return cxl_mem_cdat_read_table(cxlds, &cxlmd->cdat);
>  }
>  
> +static int read_cdat_data(struct cxl_memdev *cxlmd,
> +			  struct cxl_dev_state *cxlds)
> +{
> +	int retries = 2;
> +	int rc;
> +
> +	while (--retries) {

You either want retries--, or retries = 3...

> +		rc = __read_cdat_data(cxlmd, cxlds);
> +		if (!rc)
> +			break;
> +	}
> +	return rc;
> +}
> +
>  struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
>  {
>  	struct cxl_memdev *cxlmd;
> -- 
> 2.31.1
>