Re: [PATCH v2] tracing: fprobe: do not zero out unused fgraph_data

[Steven Rostedt]

On Tue, 24 Mar 2026 09:47:08 +0100
Martin Kaiser <martin@xxxxxxxxx> wrote:

Hi Martin,

First, please do not send a v2 as a reply to v1. A new version should
always start a new mail thread.

> If fprobe_entry does not fill the allocated fgraph_data completely, the
> unused part does not have to be zeroed.
> 
> fgraph_data is a short-lived part of the shadow stack. The preceding
> length field allows locating the end regardless of the content.
> 
> Signed-off-by: Martin Kaiser <martin@xxxxxxxxx>
> ---
> v2:

But to maintain a link to the previous version, I recommend adding here:

Changes since v1: https://lore.kernel.org/all/20260324084804.375764-1-martin@xxxxxxxxx


>  - remove the memset instead of fixing the length
> 
>  kernel/trace/fprobe.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index dcadf1d23b8a..56d145017902 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -450,8 +450,6 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops
>  				used += FPROBE_HEADER_SIZE_IN_LONG + size_words;
>  		}
>  	}
> -	if (used < reserved_words)
> -		memset(fgraph_data + used, 0, reserved_words - used);
>  
>  	/* If any exit_handler is set, data must be used. */
>  	return used != 0;

As for the patch,

Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

-- Steve