[libcamera-devel] [PATCH 1/7] ipa: raspberrypi: AWB: Remove unnecessary locking for AWB settings

[Laurent Pinchart]

Hi David,

Thank you for the patch.

On Thu, Feb 04, 2021 at 09:34:51AM +0000, David Plowman wrote:
> AWB settings get updated synchronously with the main thread, so the
> settings_mutex_ and associated locking can be removed.
> 
> Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  src/ipa/raspberrypi/controller/rpi/awb.cpp | 18 +++++-------------
>  src/ipa/raspberrypi/controller/rpi/awb.hpp |  4 +---
>  2 files changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/src/ipa/raspberrypi/controller/rpi/awb.cpp b/src/ipa/raspberrypi/controller/rpi/awb.cpp
> index 62337b13..dabab726 100644
> --- a/src/ipa/raspberrypi/controller/rpi/awb.cpp
> +++ b/src/ipa/raspberrypi/controller/rpi/awb.cpp
> @@ -185,13 +185,11 @@ unsigned int Awb::GetConvergenceFrames() const
>  
>  void Awb::SetMode(std::string const &mode_name)
>  {
> -	std::unique_lock<std::mutex> lock(settings_mutex_);
>  	mode_name_ = mode_name;
>  }
>  
>  void Awb::SetManualGains(double manual_r, double manual_b)
>  {
> -	std::unique_lock<std::mutex> lock(settings_mutex_);
>  	// If any of these are 0.0, we swich back to auto.
>  	manual_r_ = manual_r;
>  	manual_b_ = manual_b;

This patch looks good overall, but I think we have a race condition here
as manual_r_ and manual_b_ are accessed in the AWB thread, without any
lock. It's not a new issue introduced by this patch, so

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

but it should be fixed.

> @@ -229,14 +227,13 @@ void Awb::fetchAsyncResults()
>  	sync_results_ = async_results_;
>  }
>  
> -void Awb::restartAsync(StatisticsPtr &stats, std::string const &mode_name,
> -		       double lux)
> +void Awb::restartAsync(StatisticsPtr &stats, double lux)
>  {
>  	LOG(RPiAwb, Debug) << "Starting AWB calculation";
>  	// this makes a new reference which belongs to the asynchronous thread
>  	statistics_ = stats;
>  	// store the mode as it could technically change
> -	auto m = config_.modes.find(mode_name);
> +	auto m = config_.modes.find(mode_name_);
>  	mode_ = m != config_.modes.end()
>  			? &m->second
>  			: (mode_ == nullptr ? config_.default_mode : mode_);
> @@ -244,8 +241,8 @@ void Awb::restartAsync(StatisticsPtr &stats, std::string const &mode_name,
>  	frame_phase_ = 0;
>  	async_start_ = true;
>  	async_started_ = true;
> -	size_t len = mode_name.copy(async_results_.mode,
> -				    sizeof(async_results_.mode) - 1);
> +	size_t len = mode_name_.copy(async_results_.mode,
> +				     sizeof(async_results_.mode) - 1);
>  	async_results_.mode[len] = '\0';
>  	async_signal_.notify_one();
>  }
> @@ -294,11 +291,6 @@ void Awb::Process(StatisticsPtr &stats, Metadata *image_metadata)
>  	if (frame_phase_ >= (int)config_.frame_period ||
>  	    frame_count2_ < (int)config_.startup_frames) {
>  		// Update any settings and any image metadata that we need.
> -		std::string mode_name;
> -		{
> -			std::unique_lock<std::mutex> lock(settings_mutex_);
> -			mode_name = mode_name_;
> -		}
>  		struct LuxStatus lux_status = {};
>  		lux_status.lux = 400; // in case no metadata
>  		if (image_metadata->Get("lux.status", lux_status) != 0)
> @@ -307,7 +299,7 @@ void Awb::Process(StatisticsPtr &stats, Metadata *image_metadata)
>  
>  		std::unique_lock<std::mutex> lock(mutex_);
>  		if (async_started_ == false)
> -			restartAsync(stats, mode_name, lux_status.lux);
> +			restartAsync(stats, lux_status.lux);
>  	}
>  }
>  
> diff --git a/src/ipa/raspberrypi/controller/rpi/awb.hpp b/src/ipa/raspberrypi/controller/rpi/awb.hpp
> index 83b81498..1b39ab4b 100644
> --- a/src/ipa/raspberrypi/controller/rpi/awb.hpp
> +++ b/src/ipa/raspberrypi/controller/rpi/awb.hpp
> @@ -134,11 +134,9 @@ private:
>  	AwbStatus sync_results_;
>  	AwbStatus prev_sync_results_;
>  	std::string mode_name_;
> -	std::mutex settings_mutex_;
>  	// The following are for the asynchronous thread to use, though the main
>  	// thread can set/reset them if the async thread is known to be idle:
> -	void restartAsync(StatisticsPtr &stats, std::string const &mode_name,
> -			  double lux);
> +	void restartAsync(StatisticsPtr &stats, double lux);
>  	// copy out the results from the async thread so that it can be restarted
>  	void fetchAsyncResults();
>  	StatisticsPtr statistics_;

-- 
Regards,

Laurent Pinchart