Re: [PATCH v2 25/40] tracing: Add support for dynamic tracepoints

[Mathieu Desnoyers]

----- On Sep 5, 2017, at 5:57 PM, Tom Zanussi tom.zanussi@xxxxxxxxxxxxxxx wrote:

> The tracepoint infrastructure assumes statically-defined tracepoints
> and uses static_keys for tracepoint enablement.  In order to define
> tracepoints on the fly, we need to have a dynamic counterpart.
> 
> Add a 'dynamic' flag to struct tracepoint along with accompanying
> logic for this purpose.
> 
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> ---
> include/linux/tracepoint-defs.h |  1 +
> kernel/tracepoint.c             | 18 +++++++++++++-----
> 2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> index a031920..bc22d54 100644
> --- a/include/linux/tracepoint-defs.h
> +++ b/include/linux/tracepoint-defs.h
> @@ -32,6 +32,7 @@ struct tracepoint {
> 	int (*regfunc)(void);
> 	void (*unregfunc)(void);
> 	struct tracepoint_func __rcu *funcs;
> +	bool dynamic;
> };
> 
> #endif
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 685c50a..1c5957f 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -197,7 +197,9 @@ static int tracepoint_add_func(struct tracepoint *tp,
> 	struct tracepoint_func *old, *tp_funcs;
> 	int ret;
> 
> -	if (tp->regfunc && !static_key_enabled(&tp->key)) {
> +	if (tp->regfunc &&
> +	    ((tp->dynamic && !(atomic_read(&tp->key.enabled) > 0)) ||
> +	     !static_key_enabled(&tp->key))) {
> 		ret = tp->regfunc();
> 		if (ret < 0)
> 			return ret;
> @@ -219,7 +221,9 @@ static int tracepoint_add_func(struct tracepoint *tp,
> 	 * is used.
> 	 */
> 	rcu_assign_pointer(tp->funcs, tp_funcs);
> -	if (!static_key_enabled(&tp->key))
> +	if (tp->dynamic && !(atomic_read(&tp->key.enabled) > 0))
> +		atomic_inc(&tp->key.enabled);
> +	else if (!tp->dynamic && !static_key_enabled(&tp->key))
> 		static_key_slow_inc(&tp->key);
> 	release_probes(old);
> 	return 0;
> @@ -246,10 +250,14 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> 
> 	if (!tp_funcs) {
> 		/* Removed last function */
> -		if (tp->unregfunc && static_key_enabled(&tp->key))
> +		if (tp->unregfunc &&
> +		    ((tp->dynamic && (atomic_read(&tp->key.enabled) > 0)) ||
> +		     static_key_enabled(&tp->key)))
> 			tp->unregfunc();
> 
> -		if (static_key_enabled(&tp->key))
> +		if (tp->dynamic && (atomic_read(&tp->key.enabled) > 0))
> +			atomic_dec(&tp->key.enabled);
> +		else if (!tp->dynamic && static_key_enabled(&tp->key))
> 			static_key_slow_dec(&tp->key);
> 	}
> 	rcu_assign_pointer(tp->funcs, tp_funcs);
> @@ -258,7 +266,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> }
> 
> /**
> - * tracepoint_probe_register -  Connect a probe to a tracepoint
> + * tracepoint_probe_register_prio -  Connect a probe to a tracepoint
>  * @tp: tracepoint
>  * @probe: probe handler
>  * @data: tracepoint data

Hi Tom,

Thanks for updating your approach to dynamic tracepoints.

Since you're fixing up this comment above tracepoint_probe_register_prio,
can you also remove the following line above tracepoint_probe_register
while you are at it ?

 * @prio: priority of this function over other registered functions

only the tracepoint_probe_register_prio function has the "prio" parameter.

Thanks!

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com