[PATCH v4 06/20] coresight: add try_get_module() in coresight_grab_device()

[Mike Leach]

Hi Tingwei,

On Thu, 23 Jul 2020 at 05:28, Tingwei Zhang <tingwei at codeaurora.org> wrote:
>
> When coresight device is in an active session, driver module of
> that device should not be removed. Use try_get_module() in
> coresight_grab_device() to prevent module to be unloaded.
>
> Signed-off-by: Tingwei Zhang <tingwei at codeaurora.org>
> ---
>  drivers/hwtracing/coresight/coresight.c | 27 +++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index b7151c5f81b1..17bc76ea86ae 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -640,7 +640,7 @@ struct coresight_device *coresight_get_sink_by_id(u32 id)
>   * don't appear on the trace path, they should be handled along with the
>   * the master device.
>   */
> -static void coresight_grab_device(struct coresight_device *csdev)
> +static int coresight_grab_device(struct coresight_device *csdev)
>  {
>         int i;
>
> @@ -648,10 +648,25 @@ static void coresight_grab_device(struct coresight_device *csdev)
>                 struct coresight_device *child;
>
>                 child  = csdev->pdata->conns[i].child_dev;
> -               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> +               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER) {
> +                       if (!try_module_get(child->dev.parent->driver->owner))
> +                               goto err;
>                         pm_runtime_get_sync(child->dev.parent);
> +               }
>         }
> +       if (!try_module_get(csdev->dev.parent->driver->owner))
> +               goto err;
>         pm_runtime_get_sync(csdev->dev.parent);
> +       return 0;
> +err:
> +       for (i--; i >= 0; i--) {
> +               struct coresight_device *child;
> +
> +               child  = csdev->pdata->conns[i].child_dev;
> +               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> +                       pm_runtime_put(child->dev.parent);
> +       }
> +       return -ENODEV;
>  }
>
>  /*
> @@ -663,12 +678,15 @@ static void coresight_drop_device(struct coresight_device *csdev)
>         int i;
>
>         pm_runtime_put(csdev->dev.parent);
> +       module_put(csdev->dev.parent->driver->owner);
>         for (i = 0; i < csdev->pdata->nr_outport; i++) {
>                 struct coresight_device *child;
>
>                 child  = csdev->pdata->conns[i].child_dev;
> -               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER)
> +               if (child && child->type == CORESIGHT_DEV_TYPE_HELPER) {
>                         pm_runtime_put(child->dev.parent);
> +                       module_put(child->dev.parent->driver->owner);
> +               }
>         }
>  }
>
> @@ -721,7 +739,8 @@ static int _coresight_build_path(struct coresight_device *csdev,
>         if (!node)
>                 return -ENOMEM;
>
> -       coresight_grab_device(csdev);
> +       if (coresight_grab_device(csdev))
> +               return -ENODEV;
>         node->csdev = csdev;
>         list_add(&node->link, path);
>
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>

The CTI devices are associated with other coresight components using
csdev->ect_dev; These are not handled in the main linear trace path as
these have a star topology interlinking all components.
However, when a component has an associated ect_dev then is enabled at
the same time as the other component is enabled.

So a module_get/put will be needed for this association to prevent the
CTI being removed while a trace session is active.
I suggest in coresight.c : coresight_control_assoc_ectdev()

Regards

Mike


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK