netdev - Re: [PATCH v9 14/27] sfc: create type2 cxl memdev

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Message-ID: <678b14cf84ccf_20fa294f4@dwillia2-xfh.jf.intel.com.notmuch>
Date: Fri, 17 Jan 2025 18:41:19 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: <alejandro.lucero-palau@....com>, <linux-cxl@...r.kernel.org>,
	<netdev@...r.kernel.org>, <dan.j.williams@...el.com>, <edward.cree@....com>,
	<davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<edumazet@...gle.com>, <dave.jiang@...el.com>
CC: Alejandro Lucero <alucerop@....com>
Subject: Re: [PATCH v9 14/27] sfc: create type2 cxl memdev

alejandro.lucero-palau@ wrote:
> From: Alejandro Lucero <alucerop@....com>
> 
> Use cxl API for creating a cxl memory device using the type2
> cxl_dev_state struct.
> 
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> Reviewed-by: Martin Habets <habetsm.xilinx@...il.com>
> Reviewed-by: Fan Ni <fan.ni@...sung.com>
> Acked-by: Edward Cree <ecree.xilinx@...il.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>  drivers/net/ethernet/sfc/efx_cxl.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/sfc/efx_cxl.c b/drivers/net/ethernet/sfc/efx_cxl.c
> index 911f29b91bd3..f4bf137fd878 100644
> --- a/drivers/net/ethernet/sfc/efx_cxl.c
> +++ b/drivers/net/ethernet/sfc/efx_cxl.c
> @@ -96,10 +96,19 @@ int efx_cxl_init(struct efx_probe_data *probe_data)
>  	 */
>  	cxl_set_media_ready(cxl->cxlds);

It is unfortunate the media_ready is just being used as an
offline/online flag for memdevs. I would be open to just switching to
typical device online/offline semantics and drop the "media_ready" flag.

>  
> +	cxl->cxlmd = devm_cxl_add_memdev(&pci_dev->dev, cxl->cxlds);
> +	if (IS_ERR(cxl->cxlmd)) {
> +		pci_err(pci_dev, "CXL accel memdev creation failed");
> +		rc = PTR_ERR(cxl->cxlmd);
> +		goto err_memdev;
> +	}
> +
>  	probe_data->cxl = cxl;
>  
>  	return 0;
>  
> +err_memdev:
> +	cxl_release_resource(cxl->cxlds, CXL_RES_RAM);
>  err_resource_set:
>  	kfree(cxl->cxlds);

In general a function should not mix devm and goto as that is a recipe
for bugs.

The bug I see here is that devm_cxl_add_memdev() runs the teardown flow
*after* efx_pci_probe() returns an error code. That happens in
device_unbind_cleanup(), but when it goes to cleanup endpoint decoders
and anything else that might reference @cxlds it crashes because @cxlds
is long gone.

So if you use devm_cxl_add_memdev() then cxlds must be devm allocated as
well to make sure it gets freed in the proper reverse order.