linux-kernel - Re: [PATCH 3/8] rtla/osnoise_top: Fix segmentation fault when failing to enable -t

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Date:   Thu, 3 Feb 2022 11:41:26 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-devel@...r.kernel.org
Subject: Re: [PATCH 3/8] rtla/osnoise_top: Fix segmentation fault when
 failing to enable -t

On Mon, 24 Jan 2022 15:24:06 +0100
Daniel Bristot de Oliveira <bristot@...nel.org> wrote:

> rtla osnoise top is causing a segmentation fault when running with
> the --trace option on a kernel that does not support multiple
> instances. For example:
> 
>     [root@f34 rtla]# rtla osnoise top -t
>     failed to enable the tracer osnoise
>     Could not enable osnoiser tracer for tracing
>     Failed to enable the trace instance
>     Segmentation fault (core dumped)
> 
> This error happens because the exit code of the tools is trying
> to destroy the trace instance that failed to be created.
> 
> Rearrange the order in which trace instances are destroyed to avoid
> this problem.
> 
> Fixes: 1eceb2fc2ca5 ("rtla/osnoise: Add osnoise top mode")
> Cc: Daniel Bristot de Oliveira <bristot@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-trace-devel@...r.kernel.org
> Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
> ---
>  tools/tracing/rtla/src/osnoise_top.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/tracing/rtla/src/osnoise_top.c b/tools/tracing/rtla/src/osnoise_top.c
> index 332b2ac205fc..546769bc7ff7 100644
> --- a/tools/tracing/rtla/src/osnoise_top.c
> +++ b/tools/tracing/rtla/src/osnoise_top.c
> @@ -546,7 +546,7 @@ int osnoise_top_main(int argc, char **argv)
>  						    trace);
>  		if (retval < 0) {
>  			err_msg("Error iterating on events\n");
> -			goto out_top;
> +			goto out_trace;
>  		}
>  
>  		if (!params->quiet)
> @@ -569,11 +569,12 @@ int osnoise_top_main(int argc, char **argv)
>  		}
>  	}
>  
> +out_trace:
> +	if (params->trace_output)
> +		osnoise_destroy_tool(record);
>  out_top:
>  	osnoise_free_top(tool->data);
>  	osnoise_destroy_tool(tool);
> -	if (params->trace_output)
> -		osnoise_destroy_tool(record);

Wouldn't these four patches be more robust if you just initialized record
(and tool) to NULL, and change osnoise_destroy_tool() to:

void osnoise_destroy_tool(struct osnoise_tool *top)
{
	if (!top)
		return;

        trace_instance_destroy(&top->trace);

        if (top->context)
                osnoise_put_context(top->context);

        free(top);
}

Then you don't need these extra labels and if statements in the main code.

-- Steve


>  out_exit:
>  	exit(return_value);
>  }