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

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Date:   Tue, 1 Feb 2022 14:31:59 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Ben Widawsky <ben.widawsky@...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 Tue, Feb 01, 2022 at 10:59:28AM -0800, Widawsky, Ben wrote:
> 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.

Not a bad idea.

> 
> > 
> > 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...

Opps yea.

Thanks,
Ira

> 
> > +		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
> >