netdev - Re: [PATCH v17 10/22] cx/memdev: Indicate probe deferral

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Message-ID: <20250630172005.0000747c@huawei.com>
Date: Mon, 30 Jun 2025 17:20:05 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Dave Jiang <dave.jiang@...el.com>
CC: <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>, Alejandro Lucero <alucerop@....com>
Subject: Re: [PATCH v17 10/22] cx/memdev: Indicate probe deferral

Hi Dave,

> > +/*
> > + * Try to get a locked reference on a memdev's CXL port topology
> > + * connection. Be careful to observe when cxl_mem_probe() has deposited
> > + * a probe deferral awaiting the arrival of the CXL root driver.
> > + */
> > +struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd)  
> 
Just focusing on this part.

> Annotation of __acquires() is needed here to annotate that this function is taking multiple locks and keeping the locks.

Messy because it's a conditional case and on error we never have
a call marked __releases() so sparse may moan.

In theory we have __cond_acquires() but I think the sparse tooling
is still missing for that.

One option is to hike the thing into a header as inline and use __acquire()
in the appropriate places.  Then sparse can see the markings
without problems.

https://lore.kernel.org/all/20250305161652.GA18280@noisy.programming.kicks-ass.net/

has some discussion on fixing the annotation issues around conditional locks
for LLVM but for now I think we are still stuck.

For the original __cond_acquires()
https://lore.kernel.org/all/CAHk-=wjZfO9hGqJ2_hGQG3U_XzSh9_XaXze=HgPdvJbgrvASfA@mail.gmail.com/

Linus posted sparse and kernel support but I think only the kernel bit merged
as sparse is currently (I think) unmaintained.

> 
> > +{
> > +	struct cxl_port *endpoint;
> > +	int rc = -ENXIO;
> > +
> > +	device_lock(&cxlmd->dev);  
> > +> +	endpoint = cxlmd->endpoint;  
> > +	if (!endpoint)
> > +		goto err;
> > +
> > +	if (IS_ERR(endpoint)) {
> > +		rc = PTR_ERR(endpoint);
> > +		goto err;
> > +	}
> > +
> > +	device_lock(&endpoint->dev);
> > +	if (!endpoint->dev.driver)> +		goto err_endpoint;
> > +
> > +	return endpoint;
> > +
> > +err_endpoint:
> > +	device_unlock(&endpoint->dev);
> > +err:
> > +	device_unlock(&cxlmd->dev);
> > +	return ERR_PTR(rc);
> > +}
> > +EXPORT_SYMBOL_NS_GPL(cxl_acquire_endpoint, "CXL");
> > +
> > +void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port *endpoint)  
> 
> And __releases() here to release the lock annotations
> > +{
> > +	device_unlock(&endpoint->dev);
> > +	device_unlock(&cxlmd->dev);
> > +}
> > +EXPORT_SYMBOL_NS_GPL(cxl_release_endpoint, "CXL");