Re: [PATCH 1/8] coresight: Fix issue where a source device's helpers aren't disabled

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

Hi James

On 12/12/2023 15:53, James Clark wrote:
> The linked commit reverts the change that accidentally used some sysfs
> enable/disable functions from Perf which broke the refcounting, but it
> also removes the fact that the sysfs disable function disabled the
> helpers.


> 
> Add a new wrapper function that does both which is used by both Perf and
> sysfs, and label the sysfs disable function appropriately. The naming of
> all of the functions will be tidied up later to avoid this happening
> again.
> 
> Fixes: 287e82cf69aa ("coresight: Fix crash when Perf and sysfs modes are used concurrently")

But we still don't "enable" the helpers from perf mode with this patch.
i.e., we use source_ops()->enable directly. So, I guess this patch
doesn't fix a bug as such. But that said, it would be good to
enable/disable helpers for sources, in perf mode.

Suzuki


> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-core.c  | 30 ++++++++++++++-----
>   .../hwtracing/coresight/coresight-etm-perf.c  |  2 +-
>   drivers/hwtracing/coresight/coresight-priv.h  |  2 +-
>   3 files changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index d7f0e231feb9..965bb6d4e1bf 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -441,8 +441,26 @@ static void coresight_disable_helpers(struct coresight_device *csdev)
>   	}
>   }
>   
> +/*
> + * Helper function to call source_ops(csdev)->disable and also disable the
> + * helpers.
> + *
> + * There is an imbalance between coresight_enable_path() and
> + * coresight_disable_path(). Enabling also enables the source's helpers as part
> + * of the path, but disabling always skips the first item in the path (which is
> + * the source), so sources and their helpers don't get disabled as part of that
> + * function and we need the extra step here.
> + */
> +void coresight_disable_source(struct coresight_device *csdev, void *data)
> +{
> +	if (source_ops(csdev)->disable)
> +		source_ops(csdev)->disable(csdev, data);
> +	coresight_disable_helpers(csdev);
> +}
> +EXPORT_SYMBOL_GPL(coresight_disable_source);
> +
>   /**
> - *  coresight_disable_source - Drop the reference count by 1 and disable
> + *  coresight_disable_source_sysfs - Drop the reference count by 1 and disable
>    *  the device if there are no users left.
>    *
>    *  @csdev: The coresight device to disable
> @@ -451,17 +469,15 @@ static void coresight_disable_helpers(struct coresight_device *csdev)
>    *
>    *  Returns true if the device has been disabled.
>    */
> -bool coresight_disable_source(struct coresight_device *csdev, void *data)
> +static bool coresight_disable_source_sysfs(struct coresight_device *csdev,
> +					   void *data)
>   {
>   	if (atomic_dec_return(&csdev->refcnt) == 0) {
> -		if (source_ops(csdev)->disable)
> -			source_ops(csdev)->disable(csdev, data);
> -		coresight_disable_helpers(csdev);
> +		coresight_disable_source(csdev, data);
>   		csdev->enable = false;
>   	}
>   	return !csdev->enable;
>   }
> -EXPORT_SYMBOL_GPL(coresight_disable_source);
>   
>   /*
>    * coresight_disable_path_from : Disable components in the given path beyond
> @@ -1204,7 +1220,7 @@ void coresight_disable(struct coresight_device *csdev)
>   	if (ret)
>   		goto out;
>   
> -	if (!csdev->enable || !coresight_disable_source(csdev, NULL))
> +	if (!csdev->enable || !coresight_disable_source_sysfs(csdev, NULL))
>   		goto out;
>   
>   	switch (csdev->subtype.source_subtype) {
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index a52cfcce25d6..c0c60e6a1703 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -589,7 +589,7 @@ static void etm_event_stop(struct perf_event *event, int mode)
>   		return;
>   
>   	/* stop tracer */
> -	source_ops(csdev)->disable(csdev, event);
> +	coresight_disable_source(csdev, event);

Does this result i
>   
>   	/* tell the core */
>   	event->hw.state = PERF_HES_STOPPED;
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index 767076e07970..30c051055e54 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -233,6 +233,6 @@ void coresight_set_percpu_sink(int cpu, struct coresight_device *csdev);
>   struct coresight_device *coresight_get_percpu_sink(int cpu);
>   int coresight_enable_source(struct coresight_device *csdev, enum cs_mode mode,
>   			    void *data);
> -bool coresight_disable_source(struct coresight_device *csdev, void *data);
> +void coresight_disable_source(struct coresight_device *csdev, void *data);
>   
>   #endif