Re: [PATCH] coresight: core: Fix coresight device probe failure issue

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 02/03/2022 08:01, Mao Jinlong wrote:
> It is possibe that probe failure issue happens when the device
> and its child_device's probe happens at the same time.
> In coresight_make_links, has_conns_grp is true for parent, but
> has_conns_grp is false for child device as has_conns_grp is set
> to true in coresight_create_conns_sysfs_group. The probe of parent
> device will fail at this condition. Add has_conns_grp check for
> child device before make the links and make the process from
> device_register to connection_create be atomic to avoid this
> probe failure issue.
> 
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Suggested-by: Mike Leach <mike.leach@linaro.org>
> Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
> ---
>   drivers/hwtracing/coresight/coresight-core.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 88653d1c06a4..7ce78dddfe31 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1382,7 +1382,7 @@ static int coresight_fixup_device_conns(struct coresight_device *csdev)
>   			continue;
>   		conn->child_dev =
>   			coresight_find_csdev_by_fwnode(conn->child_fwnode);
> -		if (conn->child_dev) {
> +		if (conn->child_dev && conn->child_dev->has_conns_grp) {
>   			ret = coresight_make_links(csdev, conn,
>   						   conn->child_dev);
>   			if (ret)
> @@ -1619,6 +1619,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>   	csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
>   	dev_set_name(&csdev->dev, "%s", desc->name);
>   
> +	mutex_lock(&coresight_mutex);
>   	ret = device_register(&csdev->dev);
>   	if (ret) {
>   		put_device(&csdev->dev);
> @@ -1645,8 +1646,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>   		}
>   	}
>   
> -	mutex_lock(&coresight_mutex);
> -
>   	ret = coresight_create_conns_sysfs_group(csdev);
>   	if (!ret)
>   		ret = coresight_fixup_device_conns(csdev);
> @@ -1666,6 +1665,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>   err_free_csdev:
>   	kfree(csdev);
>   err_out:
> +	mutex_unlock(&coresight_mutex);

This appears to be wrong. We may do an unlock when we didn't lock it in
the first place.
Please could you double check. Also, I think it may be neater to move
the kfree(csdev) to the only user and return straight away from there.

Cheers
Suzuki




>   	/* Cleanup the connection information */
>   	coresight_release_platform_data(NULL, desc->pdata);
>   	return ERR_PTR(ret);