linux-kernel - Re: [PATCH 2/2] cxl/region: Fix missing put_device(region

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Date: Mon, 29 Apr 2024 09:14:21 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: Li Zhijian <lizhijian@...itsu.com>, <dave@...olabs.net>,
	<jonathan.cameron@...wei.com>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
	<ira.weiny@...el.com>, <dan.j.williams@...el.com>,
	<linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Li Zhijian <lizhijian@...itsu.com>
Subject: Re: [PATCH 2/2] cxl/region: Fix missing put_device(region_dev)

Li Zhijian wrote:
> >         mutex_lock(&cxlrd->range_lock);
> >         region_dev = device_find_child(&cxlrd->cxlsd.cxld.dev, hpa,
> >                                        match_region_by_range);
> >         if (!region_dev)
> >                 cxlr = construct_region(cxlrd, cxled);
> >         else
> >                 cxlr = to_cxl_region(region_dev);
> >         mutex_unlock(&cxlrd->range_lock);
> >
> >         rc = PTR_ERR_OR_ZERO(cxlr);
> >         if (rc)
> >                 goto out;
> >
> >         if (!region_dev)
> >                 region_dev = &cxlr->dev;

This diff hunk in the commit message is very odd.  I would drop it.  We
know this builds on patch 1 where you made the above change.

> 
> When to_cxl_region(region_dev) fails, put_device(region_dev) should be
> called to decrease the reference count added by device_find_child().

I __think__ this is what Dan was pointing out but I'm not sure.

I wanted to point out that to_cxl_region() can't fail because the
device_find_child() is checking that the device is a region device.

Dan, is that what you were saying when you mentioned there were more
serious issues if to_cxl_region() were to fail?

Ira

> 
> Simply put_device(region_dev) if region_dev is valid in the error path.
> 
> Fixes: a32320b71f08 ("cxl/region: Add region autodiscovery")
> Signed-off-by: Li Zhijian <lizhijian@...itsu.com>
> ---
>  drivers/cxl/core/region.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 3c80aa263a65..75390865382f 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3117,8 +3117,9 @@ int cxl_add_to_region(struct cxl_port *root, struct cxl_endpoint_decoder *cxled)
>  				p->res);
>  	}
>  
> -	put_device(region_dev);
>  out:
> +	if (region_dev)
> +		put_device(region_dev);
>  	put_device(cxlrd_dev);
>  	return rc;
>  }
> -- 
> 2.29.2
>