linux-kernel - Re: [PATCH v8 04/16] cxl/aer: AER service driver forwards CXL error to CXL driver

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Message-ID: <20250423160443.00006ee0@huawei.com>
Date: Wed, 23 Apr 2025 16:04:43 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Terry Bowman <terry.bowman@....com>
CC: <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-pci@...r.kernel.org>, <nifan.cxl@...il.com>, <dave@...olabs.net>,
	<dave.jiang@...el.com>, <alison.schofield@...el.com>,
	<vishal.l.verma@...el.com>, <dan.j.williams@...el.com>,
	<bhelgaas@...gle.com>, <mahesh@...ux.ibm.com>, <ira.weiny@...el.com>,
	<oohall@...il.com>, <Benjamin.Cheatham@....com>, <rrichter@....com>,
	<nathan.fontenot@....com>, <Smita.KoralahalliChannabasappa@....com>,
	<lukas@...ner.de>, <ming.li@...omail.com>,
	<PradeepVineshReddy.Kodamati@....com>
Subject: Re: [PATCH v8 04/16] cxl/aer: AER service driver forwards CXL error
 to CXL driver

On Wed, 26 Mar 2025 20:47:05 -0500
Terry Bowman <terry.bowman@....com> wrote:

> The AER service driver includes a CXL-specific kfifo, intended to forward
> CXL errors to the CXL driver. However, the forwarding functionality is
> currently unimplemented. Update the AER driver to enable error forwarding
> to the CXL driver.
> 
> Modify the AER service driver's handle_error_source(), which is called from
> process_aer_err_devices(), to distinguish between PCIe and CXL errors.
> 
> Rename and update is_internal_error() to is_cxl_error(). Ensuring it
> checks both the 'struct aer_info::is_cxl' flag and the AER internal error
> masks.
> 
> If the error is a standard PCIe error then continue calling pcie_aer_handle_error()
> as done in the current AER driver.
> 
> If the error is a CXL-related error then forward it to the CXL driver for
> handling using the kfifo mechanism.
> 
> Introduce a new function forward_cxl_error(), which constructs a CXL
> protocol error context using cxl_create_prot_err_info(). This context is
> then passed to the CXL driver via kfifo using a 'struct work_struct'.
> 
> Signed-off-by: Terry Bowman <terry.bowman@....com>
Hi Terry,

Finally got back to this.  I'm not following how some of the reference
counting in here is working.  It might be fine but there is a lot
taking then dropping device references - some of which are taken again later.

> @@ -1082,10 +1094,44 @@ static void cxl_rch_enable_rcec(struct pci_dev *rcec)
>  	pci_info(rcec, "CXL: Internal errors unmasked");
>  }
>  
> +static void forward_cxl_error(struct pci_dev *_pdev, struct aer_err_info *info)
> +{
> +	int severity = info->severity;

So far this variable isn't really justified.  Maybe it makes sense later in the
series?

> +	struct cxl_prot_err_work_data wd;
> +	struct cxl_prot_error_info *err_info = &wd.err_info;

Similarly. Why not just use this directly in the call below?

> +	struct pci_dev *pdev __free(pci_dev_put) = pci_dev_get(_pdev);
Can you talk me through the reference counting?  You take one pci device reference
here.... 
> +
> +	if (!cxl_create_prot_err_info) {
> +		pci_err(pdev, "Failed. CXL-AER interface not initialized.");
> +		return;
> +	}
> +
> +	if (cxl_create_prot_err_info(pdev, severity, err_info)) {

...but the implementation of this also takes once internally.  Can we skip that
internal one and document that it is always take by the caller?

> +		pci_err(pdev, "Failed to create CXL protocol error information");
> +		return;
> +	}
> +
> +	struct device *cxl_dev __free(put_device) = get_device(err_info->dev);

Also this one.  A reference was acquired and dropped in cxl_create_prot_err_info()
followed by retaking it here.  How do we know it is still about by this call
and once we pull it off the kfifo later?

> +
> +	if (!kfifo_put(&cxl_prot_err_fifo, wd)) {
> +		pr_err_ratelimited("CXL kfifo overflow\n");
> +		return;
> +	}
> +
> +	schedule_work(cxl_prot_err_work);
> +}
> +

Thanks,

Jonathan