linux-kernel - Re: [PATCH v3 06/13] coresight: Fix loss of connection info when a module is unloaded

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Date:   Thu, 30 Mar 2023 13:42:46 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        quic_jinlmao@...cinc.com, mike.leach@...aro.org
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v3 06/13] coresight: Fix loss of connection info when a
 module is unloaded

Hi James

On 29/03/2023 12:53, James Clark wrote:
> child_fwnode should be a read only property based on the DT. If it's
> cleared on the parent device when a child is unloaded, then when the
> child is loaded again the connection won't be remade.
> 
> child_dev should be cleared instead which signifies that the connection
> should be remade when the child_fwnode registers a new coresight_device.
> 
> Similarly the reference count shouldn't be decremented as long as the
> parent device exists. The correct place to drop the reference is in
> coresight_release_platform_data() which is already done.
> 
> Signed-off-by: James Clark <james.clark@....com>

This looks like a bug in the existing driver. Please could you keep this
at the beginning of the series, so that it is easier to backport for
stable ?

Also, please add :

Fixes: 37ea1ffddffa ("coresight: Use fwnode handle instead of device names")
Fixes: 2af89ebacf29 ("coresight: Clear the connection field properly")


> ---
>   drivers/hwtracing/coresight/coresight-core.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index bfe1b93aca4e..12cbb68e8e1c 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1414,13 +1414,8 @@ static int coresight_remove_match(struct device *dev, void *data)
>   		if (csdev->dev.fwnode == conn->dest_fwnode) {
>   			iterator->orphan = true;
>   			coresight_remove_links(iterator, conn);
> -			/*
> -			 * Drop the reference to the handle for the remote
> -			 * device acquired in parsing the connections from
> -			 * platform data.
> -			 */
> -			fwnode_handle_put(conn->dest_fwnode);
> -			conn->dest_fwnode = NULL;
> +
> +			conn->dest_dev = NULL;
>   			/* No need to continue */
>   			break;
>   		}
> @@ -1553,7 +1548,6 @@ void coresight_release_platform_data(struct coresight_device *csdev,
>   		 * is going away
>   		 */
>   		fwnode_handle_put(conns[i].dest_fwnode);
> -		pdata->out_conns[i].dest_fwnode = NULL;

This change is not required, as we are freeing the pdata anyway.
Keeping this might be beneficial if someone else comes looking
for references while we are going out. I don't see how we could
hit that, but just to be safe.

Suzuki