Re: [PATCH 2/3] tracing/boottime: Fix kprobe event API usage

[Steven Rostedt <rostedt@goodmis.org>]

On Sat, 25 Apr 2020 14:49:17 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Fix boottime kprobe events to use API correctly for
> multiple events.
> 
> For example, when we set a multiprobe kprobe events in
> bootconfig like below,
> 
>   ftrace.event.kprobes.myevent {
>   	probes = "vfs_read $arg1 $arg2", "vfs_write $arg1 $arg2"
>   }
> 
> This cause an error;
> 
>   trace_boot: Failed to add probe: p:kprobes/myevent (null)  vfs_read $arg1 $arg2  vfs_write $arg1 $arg2
> 
> This shows the 1st argument becomes NULL and multiprobes
> are merged to 1 probe.
> 
> Fixes: 29a154810546 ("tracing: Change trace_boot to use kprobe_event interface")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: stable@vger.kernel.org
> ---
>  kernel/trace/trace_boot.c |   20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
> index 06d7feb5255f..9de29bb45a27 100644
> --- a/kernel/trace/trace_boot.c
> +++ b/kernel/trace/trace_boot.c
> @@ -95,24 +95,20 @@ trace_boot_add_kprobe_event(struct xbc_node *node, const char *event)
>  	struct xbc_node *anode;
>  	char buf[MAX_BUF_LEN];
>  	const char *val;
> -	int ret;
> +	int ret = 0;
>  
> -	kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
> +	xbc_node_for_each_array_value(node, "probes", anode, val) {
> +		kprobe_event_cmd_init(&cmd, buf, MAX_BUF_LEN);
>  
> -	ret = kprobe_event_gen_cmd_start(&cmd, event, NULL);
> -	if (ret)
> -		return ret;
> +		ret = kprobe_event_gen_cmd_start(&cmd, event, val);
> +		if (ret)
> +			break;

Should we break here? What about just printing an error message and
continuing to the next probe. If I start up something with a typo in
the first element, I lose all events. But if I have a typo in the last
one, I get all but that one. I rather have it just fail on the ones that
don't parse properly.

-- Steve


>  
> -	xbc_node_for_each_array_value(node, "probes", anode, val) {
> -		ret = kprobe_event_add_field(&cmd, val);
> +		ret = kprobe_event_gen_cmd_end(&cmd);
>  		if (ret)
> -			return ret;
> +			pr_err("Failed to add probe: %s\n", buf);
>  	}
>  
> -	ret = kprobe_event_gen_cmd_end(&cmd);
> -	if (ret)
> -		pr_err("Failed to add probe: %s\n", buf);
> -
>  	return ret;
>  }
>  #else