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SubjectRe: [PATCH v2 25/40] tracing: Add support for dynamic tracepoints
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Hi Mathieu,

On Tue, 2017-09-05 at 23:29 +0000, Mathieu Desnoyers wrote:
> ----- On Sep 5, 2017, at 5:57 PM, Tom Zanussi tom.zanussi@linux.intel.com 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@linux.intel.com>
> > ---
> > 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 ?
>

Sure, will do.

Thanks,

Tom


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