Re: [PATCH v3 03/16] tracing/filters: Fix false success return in process_system_preds()

[Steven Rostedt]

On Wed, 28 Oct 2026 09:43:53 +0900
"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> 
> In process_system_preds(), "fail" is initialized to true to indicate
> whether any event in the subsystem successfully applied the filter.
> However, "fail = false;" was placed at the end of the event loop outside
> the error check, unconditionally clearing "fail" on every iteration even
> when process_preds() returned an error.
> 
> As a result, if every event in the subsystem fails to match the filter
> (e.g., an invalid field), process_system_preds() returns 0 (success)
> instead of -EINVAL. Consequently, create_system_filter() considers the
> operation successful and silently resets the subsystem filter display to
> the default global filter message instead of reporting the parse error.
> 
> Move "fail = false;" into the else branch of the error check so that
> "fail" is only cleared when at least one event filter succeeds. Because
> file->filter is still replaced even when process_preds() fails, check
> !list_empty(&filter_list->list) on the fail and fail_mem paths so any
> replaced old filters are freed after an RCU grace period via
> delay_free_filter().
> 
> Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> ---
>  kernel/trace/trace_events_filter.c |   15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index f7c067a58ba4..617bc3c0bb0c 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -2354,8 +2354,10 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
>  			filter_disable(file);
>  			parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0);
>  			append_filter_err(tr, pe, filter);
> -		} else
> +		} else {
>  			event_set_filtered_flag(file);
> +			fail = false;
> +		}
>  
>  
>  		filter_item = kzalloc_obj(*filter_item);
> @@ -2370,8 +2372,6 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
>  		filter_item->filter = event_filter(file);
>  		event_set_filter(file, filter);
>  		filter = NULL;
> -
> -		fail = false;
>  	}
>  
>  	if (fail)
> @@ -2386,14 +2386,17 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
>  	return 0;
>   fail:
>  	/* No call succeeded */
> -	free_filter_list(filter_list);
> +	if (!list_empty(&filter_list->list))
> +		delay_free_filter(filter_list);
> +	else
> +		free_filter_list(filter_list);
>  	parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0);
>  	return -EINVAL;
>   fail_mem:
>  	__free_filter(filter);
>  
> -	/* If any call succeeded, we still need to sync */
> -	if (!fail)
> +	/* If any filter was replaced, we still need to sync */
> +	if (!list_empty(&filter_list->list))
>  		delay_free_filter(filter_list);
>  	else
>  		free_filter_list(filter_list);

I still prefer my suggestion which cleans up the code and gets rid of the
duplicate if statement for freeing.

  https://lore.kernel.org/all/20261026153258.5259323d@xxxxxxxxxxxxxxxxxx/

-- Steve