linux-kernel - Re: [PATCH 01/12] perf/core: Add PERF_SAMPLE_WEIGHT

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Message-ID: <YBAqYyTuqxsH8tqR@hirez.programming.kicks-ass.net>
Date:   Tue, 26 Jan 2021 15:42:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, namhyung@...nel.org, jolsa@...hat.com,
        ak@...ux.intel.com, yao.jin@...ux.intel.com
Subject: Re: [PATCH 01/12] perf/core: Add PERF_SAMPLE_WEIGHT_EXT

On Tue, Jan 19, 2021 at 12:38:20PM -0800, kan.liang@...ux.intel.com wrote:

> @@ -900,6 +901,13 @@ enum perf_event_type {
>  	 *	  char			data[size]; } && PERF_SAMPLE_AUX
>  	 *	{ u64			data_page_size;} && PERF_SAMPLE_DATA_PAGE_SIZE
>  	 *	{ u64			code_page_size;} && PERF_SAMPLE_CODE_PAGE_SIZE
> +	 *	{ union {
> +	 *		u64		weight_ext;
> +	 *		struct {
> +	 *			u64	instr_latency:16,
> +	 *				reserved:48;
> +	 *		};
> +	 *	} && PERF_SAMPLE_WEIGHT_EXT
>  	 * };
>  	 */
>  	PERF_RECORD_SAMPLE			= 9,
> @@ -1248,4 +1256,12 @@ struct perf_branch_entry {
>  		reserved:40;
>  };
>  
> +union perf_weight_ext {
> +	__u64		val;
> +	struct {
> +		__u64	instr_latency:16,
> +			reserved:48;
> +	};
> +};
> +
>  #endif /* _UAPI_LINUX_PERF_EVENT_H */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 55d1879..9363d12 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1903,6 +1903,9 @@ static void __perf_event_header_size(struct perf_event *event, u64 sample_type)
>  	if (sample_type & PERF_SAMPLE_CODE_PAGE_SIZE)
>  		size += sizeof(data->code_page_size);
>  
> +	if (sample_type & PERF_SAMPLE_WEIGHT_EXT)
> +		size += sizeof(data->weight_ext);
> +
>  	event->header_size = size;
>  }
>  
> @@ -6952,6 +6955,9 @@ void perf_output_sample(struct perf_output_handle *handle,
>  			perf_aux_sample_output(event, handle, data);
>  	}
>  
> +	if (sample_type & PERF_SAMPLE_WEIGHT_EXT)
> +		perf_output_put(handle, data->weight_ext);
> +
>  	if (!event->attr.watermark) {
>  		int wakeup_events = event->attr.wakeup_events;
>  

This patch is broken and will expose uninitialized kernel stack.