diff mbox series

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

Message ID 20240403154844.3403859-2-dave.jiang@intel.com
State Accepted
Commit 648dae58a830ecceea3b1bebf68432435980f137
Headers show
Series cxl: access_coordinate validity fixes for 6.9 | expand

Commit Message

Dave Jiang April 3, 2024, 3:47 p.m. UTC 
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(-)

Comments

Robert Richter April 26, 2024, 7:10 p.m. UTC | #1 
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
>
Dave Jiang April 26, 2024, 8:13 p.m. UTC | #2 
On 4/26/24 12:10 PM, Robert Richter wrote:
> 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.

Hi Robert,
Can you please provide the 'ls -l /sys/bus/cxl/devices/$memX' of the RCH device? Maybe the iterator may need to be tweaked for RCH topology support.

> 
> 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
>>
>
diff mbox series

Patch

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