Re: [PATCH perf-tools-next v3 5/5] perf ftrace: Filter extraneous functions in function graph tracer

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] perf ftrace: Target filter state leaks for leaf functions at non-zero depth
--

commit 1481567e7a5dda207ce5b61e39c1b59803ca97c4
Author: Aaron Tomlin <atomlin@atomlin.com>

perf ftrace: Filter extraneous functions in function graph tracer

This commit enhances perf ftrace to filter out extraneous top-level functions
and detached orphan calls from the function graph output when using a target
filter.

> diff --git a/tools/perf/util/ftrace.c b/tools/perf/util/ftrace.c
> index 5cae01a28529f..96a41077dccbf 100644
> --- a/tools/perf/util/ftrace.c
> +++ b/tools/perf/util/ftrace.c

[ ... ]

> @@ -509,6 +564,92 @@ int ftrace_process_fgraph_line(struct perf_ftrace *ftrace, const char *line, FIL
>  	has_open_brace = (strchr(func_start, '{') != NULL);
>  	has_semicolon = (strchr(func_start, ';') != NULL);
>  

[ ... ]

> +		print_line(ftrace, line, out);
> +		if (has_filter && cs->in_target && cs->depth == 0 &&
> +		    has_semicolon && !has_open_brace) {
> +			cs->in_target = false;
> +			cs->orphan_depth = 0;
> +		}
> +		return 0;
> +	}

[Severity: Medium]
When a targeted function is a leaf call (no braces, only a semicolon) and
occurs at a call stack depth greater than 0, doesn't the hardcoded check for
cs->depth == 0 prevent the filter state from resetting?

It appears that cs->in_target will remain true indefinitely if the target is
not at the root depth, causing subsequent non-targeted sibling functions and
their descendants within the same parent frame to bypass the filter and
incorrectly appear in the trace output.

[ ... ]

> @@ -645,6 +801,12 @@ int ftrace_process_fgraph_line(struct perf_ftrace *ftrace, const char *line, FIL
>  		}
>  	}
>  
> +	if (has_filter && cs->in_target && cs->depth == 0 &&
> +	    has_semicolon && !has_open_brace) {
> +		cs->in_target = false;
> +		cs->orphan_depth = 0;
> +	}
> +
>  	for (i = 0; i < num_inlines; i++)
>  		free((void *)inlined_names[i]);
>  	return 0;

[Severity: Medium]
The identical logic exists here for the use_inline code path. Should these
checks verify cs->depth == cs->target_root_depth instead of cs->depth == 0
to properly reset the filter for leaf targets at non-zero depths?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012003016.263063-1-atomlin@atomlin.com?part=5