Re: [2/2] coresight: Fix reference count for software sources

From: Mathieu Poirier
Date: Tue Mar 14 2017 - 13:41:22 EST


On 14 March 2017 at 11:32, Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> wrote:
> From: "Suzuki K. Poulose" <Suzuki.Poulose@xxxxxxx>
>
> For software sources (i.e STM), there could be multiple agents
> generating the trace data, unlike the ETMs. So we need to
> properly do the accounting for the active number of users
> to disable the device when the last user goes away. Right
> now, the reference counting is broken for sources as we skip
> the actions when we detect that the source is enabled.
>
> This patch fixes the problem by adding the refcounting for
> software sources, even when they are enabled.
>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Reported-by: Robert Walker <robert.walker@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> drivers/hwtracing/coresight/coresight.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index 34cd1ed..2da9e39 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -552,6 +552,7 @@ int coresight_enable(struct coresight_device *csdev)
> int cpu, ret = 0;
> struct coresight_device *sink;
> struct list_head *path;
> + enum coresight_dev_subtype_source subtype = csdev->subtype.source_subtype;

Checkpatch.pl complains about a line over 80 characters.

>
> mutex_lock(&coresight_mutex);
>
> @@ -559,8 +560,16 @@ int coresight_enable(struct coresight_device *csdev)
> if (ret)
> goto out;
>
> - if (csdev->enable)
> + if (csdev->enable) {
> + /*
> + * There could be multiple applications driving the software
> + * source. So keep the refcount for each such user when the
> + * source is already enabled.
> + */
> + if (subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_SOFTWARE)
> + atomic_inc(csdev->refcnt);
> goto out;
> + }
>
> /*
> * Search for a valid sink for this session but don't reset the
> @@ -587,7 +596,7 @@ int coresight_enable(struct coresight_device *csdev)
> if (ret)
> goto err_source;
>
> - switch (csdev->subtype.source_subtype) {
> + switch (subtype) {
> case CORESIGHT_DEV_SUBTYPE_SOURCE_PROC:
> /*
> * When working from sysFS it is important to keep track