Re: [PATCH v2] tracepoints: prevents null probe from being added

[Steven Rostedt]

On Thu, 2013-03-21 at 14:34 +0900, kpark3469@xxxxxxxxx wrote:
> From: Sahara <keun-o.park@xxxxxxxxxxxxx>
> 
> Somehow tracepoint_entry_add_probe function allows a null probe function.
> And, this may lead to unexpected result since the number of probe
> functions in an entry can be counted by checking whether probe is null
> or not in for-loop.
> This patch prevents the null probe from being added.
> In tracepoint_entry_remove_probe function, checking probe parameter
> within for-loop is moved out for code efficiency leaving the null probe
> feature which removes all probe functions in the entry.
> 
> Signed-off-by: Sahara <keun-o.park@xxxxxxxxxxxxx>
> Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> ---
>  kernel/tracepoint.c |   18 ++++++++++--------
>  1 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 0c05a45..7d69348 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -112,7 +112,8 @@ tracepoint_entry_add_probe(struct tracepoint_entry *entry,
>  	int nr_probes = 0;
>  	struct tracepoint_func *old, *new;
>  
> -	WARN_ON(!probe);
> +	if (WARN_ON(!probe))
> +		return ERR_PTR(-EINVAL);
>  
>  	debug_print_probes(entry);
>  	old = entry->funcs;
> @@ -152,13 +153,15 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
>  
>  	debug_print_probes(entry);
>  	/* (N -> M), (N > 1, M >= 0) probes */
> -	for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> -		if (!probe ||
> -		    (old[nr_probes].func == probe &&
> -		     old[nr_probes].data == data))
> -			nr_del++;
> +	if (probe) {
> +		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
> +			if (old[nr_probes].func == probe &&
> +			     old[nr_probes].data == data)
> +				nr_del++;
> +		}
>  	}
>  
> +	/* If probe is NULL, all funcs in the entry will be removed. */

OK, I first thought this was a bug as nr_del would be zero and not match
nr_probes, but then I realized that nr_probes would also be zero. Can
you update the above comment to say something like:

	/*
	 * If probe is NULL, then nr_probes = nr_del = 0, and then the
	 * entire entry will be removed.
	 */

Thanks,

-- Steve

>  	if (nr_probes - nr_del == 0) {
>  		/* N -> 0, (N > 1) */
>  		entry->funcs = NULL;
> @@ -173,8 +176,7 @@ tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
>  		if (new == NULL)
>  			return ERR_PTR(-ENOMEM);
>  		for (i = 0; old[i].func; i++)
> -			if (probe &&
> -			    (old[i].func != probe || old[i].data != data))
> +			if (old[i].func != probe || old[i].data != data)
>  				new[j++] = old[i];
>  		new[nr_probes - nr_del].func = NULL;
>  		entry->refcount = nr_probes - nr_del;


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