linux-kernel - Re: [PATCH V2 04/11] cxl/mem: Clear events on driver load

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Date:   Thu, 1 Dec 2022 09:02:01 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Davidlohr Bueso" <dave@...olabs.net>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH V2 04/11] cxl/mem: Clear events on driver load

On Thu, Dec 01, 2022 at 01:30:33PM +0000, Jonathan Cameron wrote:
> On Wed, 30 Nov 2022 16:27:12 -0800
> ira.weiny@...el.com wrote:
> 
> > From: Ira Weiny <ira.weiny@...el.com>
> > 
> > The information contained in the events prior to the driver loading can
> > be queried at any time through other mailbox commands.
> > 
> > Ensure a clean slate of events by reading and clearing the events.  The
> > events are sent to the trace buffer but it is not anticipated to have
> > anyone listening to it at driver load time.
> > 
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> Probably not worth addressing but there is a corner case where this might fail
> if some broken software already messed with reading out the events.

Yea they can keep the pieces if they have done that.

> 
> Imagine it read the first mailbox sized chunk, but didn't clear them...
> 
> If that happens, then we'd end up seeing the whole list, but in non
> temporal order and hence trying to clear them out of order with predictable
> fails.
> 
> Maybe this is the category of things we 'fix' if we ever hear of it actually
> happening.
> 
> So with that caveat called out so I can say 'I told you so' :), fine to keep my tag on this.

Sure!  We probably owe you this T-Shirt already!

https://www.amazon.com/Big-Bang-Theory-Informed-Thusly/dp/B06XYCSQRF

:-D

Ira

> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> >  drivers/cxl/pci.c            | 2 ++
> >  tools/testing/cxl/test/mem.c | 2 ++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> > index 8f86f85d89c7..11e95a95195a 100644
> > --- a/drivers/cxl/pci.c
> > +++ b/drivers/cxl/pci.c
> > @@ -521,6 +521,8 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  	if (IS_ERR(cxlmd))
> >  		return PTR_ERR(cxlmd);
> >  
> > +	cxl_mem_get_event_records(cxlds);
> > +
> >  	if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM))
> >  		rc = devm_cxl_add_nvdimm(&pdev->dev, cxlmd);
> >  
> > diff --git a/tools/testing/cxl/test/mem.c b/tools/testing/cxl/test/mem.c
> > index aa2df3a15051..e2f5445d24ff 100644
> > --- a/tools/testing/cxl/test/mem.c
> > +++ b/tools/testing/cxl/test/mem.c
> > @@ -285,6 +285,8 @@ static int cxl_mock_mem_probe(struct platform_device *pdev)
> >  	if (IS_ERR(cxlmd))
> >  		return PTR_ERR(cxlmd);
> >  
> > +	cxl_mem_get_event_records(cxlds);
> > +
> >  	if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM))
> >  		rc = devm_cxl_add_nvdimm(dev, cxlmd);
> >  
>