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

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Message-ID: <20250425141849.00003c92@huawei.com>
Date: Fri, 25 Apr 2025 14:18:49 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: "Bowman, Terry" <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 Thu, 24 Apr 2025 09:17:45 -0500
"Bowman, Terry" <terry.bowman@....com> wrote:

> On 4/23/2025 10:04 AM, Jonathan Cameron wrote:
> > 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?  
> 
> This is used below in call to cxl_create_prot_err_info().
Sure, but why not just do

if (cxl_create_prot_error_info(pdev, info->severity, &wd.err_info)) {

There isn't anything modifying info->severity in between so that local
variable is just padding out the code to no real benefit.


> 
> >> +		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?  
> 
> Yes, this is a problem I realized after sending the series.
> 
> The device reference incr could be changed for all the devices to the non-cleanup
> variety. Then would add the reference incr in the caller after calling cxl_create_prot_err_info().
> I need to look at the other calls to to cxl_create_prot_err_info() as well.
> 
> In addition, I think we should consider adding the CXL RAS status into the struct cxl_prot_err_info.
> This would eliminate the need for further accesses to the CXL device after being dequeued from the
> fifo. Thoughts?

That sounds like a reasonable solution to me.

Jonathan