Re: [PATCH v7 1/5] cxl: Remove checking of iter in cxl_endpoint_get_perf_coordinates()

[Robert Richter <rrichter@amd.com>]

On 03.04.24 08:47:12, Dave Jiang wrote:
> The while() loop in cxl_endpoint_get_perf_coordinates() checks to see if
> 'iter' is valid as part of the condition breaking out of the loop.
> is_cxl_root() will stop the loop before the next iteration could go NULL.
> Remove the iter check.
> 
> The presence of the iter or removing the iter does not impact the behavior
> of the code. This is a code clean up and not a bug fix.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/cxl/core/port.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 2b0cab556072..6cbde50a742b 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -2197,7 +2197,7 @@ int cxl_endpoint_get_perf_coordinates(struct cxl_port *port,
>  	 * port each iteration. If the parent is cxl root then there is
>  	 * nothing to gather.
>  	 */
> -	while (iter && !is_cxl_root(to_cxl_port(iter->dev.parent))) {
> +	while (!is_cxl_root(to_cxl_port(iter->dev.parent))) {

I am seeing the following mainline after [1]:

 [   39.815379] cxl_acpi ACPI0017:00: not a cxl_port device
 [   39.827123] WARNING: CPU: 46 PID: 1754 at drivers/cxl/core/port.c:592 to_cxl_port+0x56/0x70 [cxl_core]

... plus some related subsequent NULL pointer dereference:

 [   40.718708] BUG: kernel NULL pointer dereference, address: 00000000000002d8

This changes looks related. I am going to dig deeper here but just a
headsup in advance.

Note this is tested on an RCH topology.

Thanks,

-Robert

[1] commit 586b5dfb51b9 ("Merge tag 'cxl-fixes-6.9-rc4' of
    git://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl"):

>  		cxl_coordinates_combine(&c, &c, &dport->sw_coord);
>  		c.write_latency += dport->link_latency;
>  		c.read_latency += dport->link_latency;
> -- 
> 2.44.0
>