To ultimately allow bpf programs attached to perf events to completely
suppress all of the effects of a perf event overflow (rather than just the
sample output, as they do today), call bpf_overflow_handler() from
__perf_event_overflow() directly rather than modifying struct perf_event's
overflow_handler. Return the bpf program's return value from
bpf_overflow_handler() so that __perf_event_overflow() knows how to
proceed. Remove the now unnecessary orig_overflow_handler from struct
perf_event.

This patch is solely a refactoring and results in no behavior change.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Suggested-by: Namhyung Kim <namhyung@kernel.org>
---
 include/linux/perf_event.h |  6 +-----
 kernel/events/core.c       | 28 +++++++++++++++-------------
 2 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 5547ba68e6e4..312b9f31442c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -810,7 +810,6 @@ struct perf_event {
 	perf_overflow_handler_t		overflow_handler;
 	void				*overflow_handler_context;
 #ifdef CONFIG_BPF_SYSCALL
-	perf_overflow_handler_t		orig_overflow_handler;
 	struct bpf_prog			*prog;
 	u64				bpf_cookie;
 #endif
@@ -1337,10 +1336,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
 #ifdef CONFIG_BPF_SYSCALL
 static inline bool uses_default_overflow_handler(struct perf_event *event)
 {
-	if (likely(is_default_overflow_handler(event)))
-		return true;
-
-	return __is_default_overflow_handler(event->orig_overflow_handler);
+	return is_default_overflow_handler(event);
 }
 #else
 #define uses_default_overflow_handler(event) \
diff --git a/kernel/events/core.c b/kernel/events/core.c
index b704d83a28b2..54f6372d2634 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9515,6 +9515,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
 	return true;
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static int bpf_overflow_handler(struct perf_event *event,
+				struct perf_sample_data *data,
+				struct pt_regs *regs);
+#endif
+
 /*
  * Generic event overflow handling, sampling.
  */
@@ -9584,7 +9590,10 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending_irq);
 	}
 
-	READ_ONCE(event->overflow_handler)(event, data, regs);
+#ifdef CONFIG_BPF_SYSCALL
+	if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
+#endif
+		READ_ONCE(event->overflow_handler)(event, data, regs);
 
 	if (*perf_event_fasync(event) && event->pending_kill) {
 		event->pending_wakeup = 1;
@@ -10394,9 +10403,9 @@ static void perf_event_free_filter(struct perf_event *event)
 }
 
 #ifdef CONFIG_BPF_SYSCALL
-static void bpf_overflow_handler(struct perf_event *event,
-				 struct perf_sample_data *data,
-				 struct pt_regs *regs)
+static int bpf_overflow_handler(struct perf_event *event,
+				struct perf_sample_data *data,
+				struct pt_regs *regs)
 {
 	struct bpf_perf_event_data_kern ctx = {
 		.data = data,
@@ -10417,10 +10426,8 @@ static void bpf_overflow_handler(struct perf_event *event,
 	rcu_read_unlock();
 out:
 	__this_cpu_dec(bpf_prog_active);
-	if (!ret)
-		return;
 
-	event->orig_overflow_handler(event, data, regs);
+	return ret;
 }
 
 static int perf_event_set_bpf_handler(struct perf_event *event,
@@ -10456,8 +10463,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
 
 	event->prog = prog;
 	event->bpf_cookie = bpf_cookie;
-	event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
-	WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
 	return 0;
 }
 
@@ -10468,7 +10473,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
 	if (!prog)
 		return;
 
-	WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
 	event->prog = NULL;
 	bpf_prog_put(prog);
 }
@@ -11928,13 +11932,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		overflow_handler = parent_event->overflow_handler;
 		context = parent_event->overflow_handler_context;
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
-		if (overflow_handler == bpf_overflow_handler) {
+		if (parent_event->prog) {
 			struct bpf_prog *prog = parent_event->prog;
 
 			bpf_prog_inc(prog);
 			event->prog = prog;
-			event->orig_overflow_handler =
-				parent_event->orig_overflow_handler;
 		}
 #endif
 	}
-- 
2.34.1

On Sun, Dec 10, 2023 at 8:55 PM Kyle Huey <me@kylehuey.com> wrote:
>
> To ultimately allow bpf programs attached to perf events to completely
> suppress all of the effects of a perf event overflow (rather than just the
> sample output, as they do today), call bpf_overflow_handler() from
> __perf_event_overflow() directly rather than modifying struct perf_event's
> overflow_handler. Return the bpf program's return value from
> bpf_overflow_handler() so that __perf_event_overflow() knows how to
> proceed. Remove the now unnecessary orig_overflow_handler from struct
> perf_event.
>
> This patch is solely a refactoring and results in no behavior change.
>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> Suggested-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  include/linux/perf_event.h |  6 +-----
>  kernel/events/core.c       | 28 +++++++++++++++-------------
>  2 files changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 5547ba68e6e4..312b9f31442c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -810,7 +810,6 @@ struct perf_event {
>         perf_overflow_handler_t         overflow_handler;
>         void                            *overflow_handler_context;
>  #ifdef CONFIG_BPF_SYSCALL
> -       perf_overflow_handler_t         orig_overflow_handler;
>         struct bpf_prog                 *prog;
>         u64                             bpf_cookie;
>  #endif
> @@ -1337,10 +1336,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
>  #ifdef CONFIG_BPF_SYSCALL
>  static inline bool uses_default_overflow_handler(struct perf_event *event)
>  {
> -       if (likely(is_default_overflow_handler(event)))
> -               return true;
> -
> -       return __is_default_overflow_handler(event->orig_overflow_handler);
> +       return is_default_overflow_handler(event);
>  }
>  #else
>  #define uses_default_overflow_handler(event) \
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b704d83a28b2..54f6372d2634 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9515,6 +9515,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
>         return true;
>  }
>
> +#ifdef CONFIG_BPF_SYSCALL
> +static int bpf_overflow_handler(struct perf_event *event,
> +                               struct perf_sample_data *data,
> +                               struct pt_regs *regs);
> +#endif
> +
>  /*
>   * Generic event overflow handling, sampling.
>   */
> @@ -9584,7 +9590,10 @@ static int __perf_event_overflow(struct perf_event *event,
>                 irq_work_queue(&event->pending_irq);
>         }
>
> -       READ_ONCE(event->overflow_handler)(event, data, regs);
> +#ifdef CONFIG_BPF_SYSCALL
> +       if (!(event->prog && !bpf_overflow_handler(event, data, regs)))

This condition is hard to follow. Please consider simplifying it.

Thanks,
Song

> +#endif
> +               READ_ONCE(event->overflow_handler)(event, data, regs);
>
>         if (*perf_event_fasync(event) && event->pending_kill) {
>                 event->pending_wakeup = 1;
> @@ -10394,9 +10403,9 @@ static void perf_event_free_filter(struct perf_event *event)
>  }
>
>  #ifdef CONFIG_BPF_SYSCALL
> -static void bpf_overflow_handler(struct perf_event *event,
> -                                struct perf_sample_data *data,
> -                                struct pt_regs *regs)
> +static int bpf_overflow_handler(struct perf_event *event,
> +                               struct perf_sample_data *data,
> +                               struct pt_regs *regs)
>  {
>         struct bpf_perf_event_data_kern ctx = {
>                 .data = data,
> @@ -10417,10 +10426,8 @@ static void bpf_overflow_handler(struct perf_event *event,
>         rcu_read_unlock();
>  out:
>         __this_cpu_dec(bpf_prog_active);
> -       if (!ret)
> -               return;
>
> -       event->orig_overflow_handler(event, data, regs);
> +       return ret;
>  }
>
>  static int perf_event_set_bpf_handler(struct perf_event *event,
> @@ -10456,8 +10463,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
>
>         event->prog = prog;
>         event->bpf_cookie = bpf_cookie;
> -       event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
> -       WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
>         return 0;
>  }
>
> @@ -10468,7 +10473,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
>         if (!prog)
>                 return;
>
> -       WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
>         event->prog = NULL;
>         bpf_prog_put(prog);
>  }
> @@ -11928,13 +11932,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
>                 overflow_handler = parent_event->overflow_handler;
>                 context = parent_event->overflow_handler_context;
>  #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
> -               if (overflow_handler == bpf_overflow_handler) {
> +               if (parent_event->prog) {
>                         struct bpf_prog *prog = parent_event->prog;
>
>                         bpf_prog_inc(prog);
>                         event->prog = prog;
> -                       event->orig_overflow_handler =
> -                               parent_event->orig_overflow_handler;
>                 }
>  #endif
>         }
> --
> 2.34.1
>
>

On Tue, Jan 2, 2024 at 3:05 PM Song Liu <song@kernel.org> wrote:
>
> On Sun, Dec 10, 2023 at 8:55 PM Kyle Huey <me@kylehuey.com> wrote:
> >
> > To ultimately allow bpf programs attached to perf events to completely
> > suppress all of the effects of a perf event overflow (rather than just the
> > sample output, as they do today), call bpf_overflow_handler() from
> > __perf_event_overflow() directly rather than modifying struct perf_event's
> > overflow_handler. Return the bpf program's return value from
> > bpf_overflow_handler() so that __perf_event_overflow() knows how to
> > proceed. Remove the now unnecessary orig_overflow_handler from struct
> > perf_event.
> >
> > This patch is solely a refactoring and results in no behavior change.
> >
> > Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> > Suggested-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  include/linux/perf_event.h |  6 +-----
> >  kernel/events/core.c       | 28 +++++++++++++++-------------
> >  2 files changed, 16 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 5547ba68e6e4..312b9f31442c 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -810,7 +810,6 @@ struct perf_event {
> >         perf_overflow_handler_t         overflow_handler;
> >         void                            *overflow_handler_context;
> >  #ifdef CONFIG_BPF_SYSCALL
> > -       perf_overflow_handler_t         orig_overflow_handler;
> >         struct bpf_prog                 *prog;
> >         u64                             bpf_cookie;
> >  #endif
> > @@ -1337,10 +1336,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
> >  #ifdef CONFIG_BPF_SYSCALL
> >  static inline bool uses_default_overflow_handler(struct perf_event *event)
> >  {
> > -       if (likely(is_default_overflow_handler(event)))
> > -               return true;
> > -
> > -       return __is_default_overflow_handler(event->orig_overflow_handler);
> > +       return is_default_overflow_handler(event);
> >  }
> >  #else
> >  #define uses_default_overflow_handler(event) \
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index b704d83a28b2..54f6372d2634 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -9515,6 +9515,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
> >         return true;
> >  }
> >
> > +#ifdef CONFIG_BPF_SYSCALL
> > +static int bpf_overflow_handler(struct perf_event *event,
> > +                               struct perf_sample_data *data,
> > +                               struct pt_regs *regs);
> > +#endif
> > +
> >  /*
> >   * Generic event overflow handling, sampling.
> >   */
> > @@ -9584,7 +9590,10 @@ static int __perf_event_overflow(struct perf_event *event,
> >                 irq_work_queue(&event->pending_irq);
> >         }
> >
> > -       READ_ONCE(event->overflow_handler)(event, data, regs);
> > +#ifdef CONFIG_BPF_SYSCALL
> > +       if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
>
> This condition is hard to follow. Please consider simplifying it.
>
> Thanks,
> Song

It gets simplified later in patch 3/4.

- Kyle

> > +#endif
> > +               READ_ONCE(event->overflow_handler)(event, data, regs);
> >
> >         if (*perf_event_fasync(event) && event->pending_kill) {
> >                 event->pending_wakeup = 1;
> > @@ -10394,9 +10403,9 @@ static void perf_event_free_filter(struct perf_event *event)
> >  }
> >
> >  #ifdef CONFIG_BPF_SYSCALL
> > -static void bpf_overflow_handler(struct perf_event *event,
> > -                                struct perf_sample_data *data,
> > -                                struct pt_regs *regs)
> > +static int bpf_overflow_handler(struct perf_event *event,
> > +                               struct perf_sample_data *data,
> > +                               struct pt_regs *regs)
> >  {
> >         struct bpf_perf_event_data_kern ctx = {
> >                 .data = data,
> > @@ -10417,10 +10426,8 @@ static void bpf_overflow_handler(struct perf_event *event,
> >         rcu_read_unlock();
> >  out:
> >         __this_cpu_dec(bpf_prog_active);
> > -       if (!ret)
> > -               return;
> >
> > -       event->orig_overflow_handler(event, data, regs);
> > +       return ret;
> >  }
> >
> >  static int perf_event_set_bpf_handler(struct perf_event *event,
> > @@ -10456,8 +10463,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
> >
> >         event->prog = prog;
> >         event->bpf_cookie = bpf_cookie;
> > -       event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
> > -       WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
> >         return 0;
> >  }
> >
> > @@ -10468,7 +10473,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
> >         if (!prog)
> >                 return;
> >
> > -       WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
> >         event->prog = NULL;
> >         bpf_prog_put(prog);
> >  }
> > @@ -11928,13 +11932,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> >                 overflow_handler = parent_event->overflow_handler;
> >                 context = parent_event->overflow_handler_context;
> >  #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
> > -               if (overflow_handler == bpf_overflow_handler) {
> > +               if (parent_event->prog) {
> >                         struct bpf_prog *prog = parent_event->prog;
> >
> >                         bpf_prog_inc(prog);
> >                         event->prog = prog;
> > -                       event->orig_overflow_handler =
> > -                               parent_event->orig_overflow_handler;
> >                 }
> >  #endif
> >         }
> > --
> > 2.34.1
> >
> >

On Sun, Dec 10, 2023 at 8:55 PM Kyle Huey <me@kylehuey.com> wrote:
>
> To ultimately allow bpf programs attached to perf events to completely
> suppress all of the effects of a perf event overflow (rather than just the
> sample output, as they do today), call bpf_overflow_handler() from
> __perf_event_overflow() directly rather than modifying struct perf_event's
> overflow_handler. Return the bpf program's return value from
> bpf_overflow_handler() so that __perf_event_overflow() knows how to
> proceed. Remove the now unnecessary orig_overflow_handler from struct
> perf_event.
>
> This patch is solely a refactoring and results in no behavior change.
>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> Suggested-by: Namhyung Kim <namhyung@kernel.org>

Acked-by: Song Liu <song@kernel.org>

On Mon, 11 Dec 2023 at 05:55, Kyle Huey <me@kylehuey.com> wrote:
>
> To ultimately allow bpf programs attached to perf events to completely
> suppress all of the effects of a perf event overflow (rather than just the
> sample output, as they do today), call bpf_overflow_handler() from
> __perf_event_overflow() directly rather than modifying struct perf_event's
> overflow_handler. Return the bpf program's return value from
> bpf_overflow_handler() so that __perf_event_overflow() knows how to
> proceed. Remove the now unnecessary orig_overflow_handler from struct
> perf_event.
>
> This patch is solely a refactoring and results in no behavior change.
>
> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> Suggested-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  include/linux/perf_event.h |  6 +-----
>  kernel/events/core.c       | 28 +++++++++++++++-------------
>  2 files changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 5547ba68e6e4..312b9f31442c 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -810,7 +810,6 @@ struct perf_event {
>         perf_overflow_handler_t         overflow_handler;
>         void                            *overflow_handler_context;
>  #ifdef CONFIG_BPF_SYSCALL
> -       perf_overflow_handler_t         orig_overflow_handler;
>         struct bpf_prog                 *prog;
>         u64                             bpf_cookie;
>  #endif
> @@ -1337,10 +1336,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
>  #ifdef CONFIG_BPF_SYSCALL
>  static inline bool uses_default_overflow_handler(struct perf_event *event)
>  {
> -       if (likely(is_default_overflow_handler(event)))
> -               return true;
> -
> -       return __is_default_overflow_handler(event->orig_overflow_handler);
> +       return is_default_overflow_handler(event);
>  }
>  #else
>  #define uses_default_overflow_handler(event) \
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b704d83a28b2..54f6372d2634 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9515,6 +9515,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
>         return true;
>  }
>
> +#ifdef CONFIG_BPF_SYSCALL
> +static int bpf_overflow_handler(struct perf_event *event,
> +                               struct perf_sample_data *data,
> +                               struct pt_regs *regs);
> +#endif

To avoid more #ifdefs we usually add a stub, something like:

#ifdef ...
static int bpf_overflow_handler(...);
#else
static inline int bpf_overflow_handler(...) { return 0; }
#endif

Then you can avoid more #ifdefs below, esp. when it surrounds an
if-statement it easily leads to confusion or subtle bugs in future
changes. The compiler will optimize out the constants and the
generated code will be the same.

>  /*
>   * Generic event overflow handling, sampling.
>   */
> @@ -9584,7 +9590,10 @@ static int __perf_event_overflow(struct perf_event *event,
>                 irq_work_queue(&event->pending_irq);
>         }
>
> -       READ_ONCE(event->overflow_handler)(event, data, regs);
> +#ifdef CONFIG_BPF_SYSCALL
> +       if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
> +#endif
> +               READ_ONCE(event->overflow_handler)(event, data, regs);
>
>         if (*perf_event_fasync(event) && event->pending_kill) {
>                 event->pending_wakeup = 1;
> @@ -10394,9 +10403,9 @@ static void perf_event_free_filter(struct perf_event *event)
>  }
>
>  #ifdef CONFIG_BPF_SYSCALL
> -static void bpf_overflow_handler(struct perf_event *event,
> -                                struct perf_sample_data *data,
> -                                struct pt_regs *regs)
> +static int bpf_overflow_handler(struct perf_event *event,
> +                               struct perf_sample_data *data,
> +                               struct pt_regs *regs)
>  {
>         struct bpf_perf_event_data_kern ctx = {
>                 .data = data,
> @@ -10417,10 +10426,8 @@ static void bpf_overflow_handler(struct perf_event *event,
>         rcu_read_unlock();
>  out:
>         __this_cpu_dec(bpf_prog_active);
> -       if (!ret)
> -               return;
>
> -       event->orig_overflow_handler(event, data, regs);
> +       return ret;
>  }
>
>  static int perf_event_set_bpf_handler(struct perf_event *event,
> @@ -10456,8 +10463,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
>
>         event->prog = prog;
>         event->bpf_cookie = bpf_cookie;
> -       event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
> -       WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
>         return 0;
>  }
>
> @@ -10468,7 +10473,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
>         if (!prog)
>                 return;
>
> -       WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
>         event->prog = NULL;
>         bpf_prog_put(prog);
>  }
> @@ -11928,13 +11932,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
>                 overflow_handler = parent_event->overflow_handler;
>                 context = parent_event->overflow_handler_context;
>  #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
> -               if (overflow_handler == bpf_overflow_handler) {
> +               if (parent_event->prog) {
>                         struct bpf_prog *prog = parent_event->prog;
>
>                         bpf_prog_inc(prog);
>                         event->prog = prog;
> -                       event->orig_overflow_handler =
> -                               parent_event->orig_overflow_handler;
>                 }
>  #endif
>         }
> --
> 2.34.1
>

On Mon, Dec 11, 2023 at 6:20 AM Marco Elver <elver@google.com> wrote:
>
> On Mon, 11 Dec 2023 at 05:55, Kyle Huey <me@kylehuey.com> wrote:
> >
> > To ultimately allow bpf programs attached to perf events to completely
> > suppress all of the effects of a perf event overflow (rather than just the
> > sample output, as they do today), call bpf_overflow_handler() from
> > __perf_event_overflow() directly rather than modifying struct perf_event's
> > overflow_handler. Return the bpf program's return value from
> > bpf_overflow_handler() so that __perf_event_overflow() knows how to
> > proceed. Remove the now unnecessary orig_overflow_handler from struct
> > perf_event.
> >
> > This patch is solely a refactoring and results in no behavior change.
> >
> > Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> > Suggested-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  include/linux/perf_event.h |  6 +-----
> >  kernel/events/core.c       | 28 +++++++++++++++-------------
> >  2 files changed, 16 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 5547ba68e6e4..312b9f31442c 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -810,7 +810,6 @@ struct perf_event {
> >         perf_overflow_handler_t         overflow_handler;
> >         void                            *overflow_handler_context;
> >  #ifdef CONFIG_BPF_SYSCALL
> > -       perf_overflow_handler_t         orig_overflow_handler;
> >         struct bpf_prog                 *prog;
> >         u64                             bpf_cookie;
> >  #endif
> > @@ -1337,10 +1336,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
> >  #ifdef CONFIG_BPF_SYSCALL
> >  static inline bool uses_default_overflow_handler(struct perf_event *event)
> >  {
> > -       if (likely(is_default_overflow_handler(event)))
> > -               return true;
> > -
> > -       return __is_default_overflow_handler(event->orig_overflow_handler);
> > +       return is_default_overflow_handler(event);
> >  }
> >  #else
> >  #define uses_default_overflow_handler(event) \
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index b704d83a28b2..54f6372d2634 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -9515,6 +9515,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
> >         return true;
> >  }
> >
> > +#ifdef CONFIG_BPF_SYSCALL
> > +static int bpf_overflow_handler(struct perf_event *event,
> > +                               struct perf_sample_data *data,
> > +                               struct pt_regs *regs);
> > +#endif
>
> To avoid more #ifdefs we usually add a stub, something like:
>
> #ifdef ...
> static int bpf_overflow_handler(...);
> #else
> static inline int bpf_overflow_handler(...) { return 0; }
> #endif
>
> Then you can avoid more #ifdefs below, esp. when it surrounds an
> if-statement it easily leads to confusion or subtle bugs in future
> changes. The compiler will optimize out the constants and the
> generated code will be the same.

This would not allow removing any #ifdefs because event->prog is only
present if CONFIG_BPF_SYSCALL is defined.

- Kyle

> >  /*
> >   * Generic event overflow handling, sampling.
> >   */
> > @@ -9584,7 +9590,10 @@ static int __perf_event_overflow(struct perf_event *event,
> >                 irq_work_queue(&event->pending_irq);
> >         }
> >
> > -       READ_ONCE(event->overflow_handler)(event, data, regs);
> > +#ifdef CONFIG_BPF_SYSCALL
> > +       if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
> > +#endif
> > +               READ_ONCE(event->overflow_handler)(event, data, regs);
> >
> >         if (*perf_event_fasync(event) && event->pending_kill) {
> >                 event->pending_wakeup = 1;
> > @@ -10394,9 +10403,9 @@ static void perf_event_free_filter(struct perf_event *event)
> >  }
> >
> >  #ifdef CONFIG_BPF_SYSCALL
> > -static void bpf_overflow_handler(struct perf_event *event,
> > -                                struct perf_sample_data *data,
> > -                                struct pt_regs *regs)
> > +static int bpf_overflow_handler(struct perf_event *event,
> > +                               struct perf_sample_data *data,
> > +                               struct pt_regs *regs)
> >  {
> >         struct bpf_perf_event_data_kern ctx = {
> >                 .data = data,
> > @@ -10417,10 +10426,8 @@ static void bpf_overflow_handler(struct perf_event *event,
> >         rcu_read_unlock();
> >  out:
> >         __this_cpu_dec(bpf_prog_active);
> > -       if (!ret)
> > -               return;
> >
> > -       event->orig_overflow_handler(event, data, regs);
> > +       return ret;
> >  }
> >
> >  static int perf_event_set_bpf_handler(struct perf_event *event,
> > @@ -10456,8 +10463,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
> >
> >         event->prog = prog;
> >         event->bpf_cookie = bpf_cookie;
> > -       event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
> > -       WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
> >         return 0;
> >  }
> >
> > @@ -10468,7 +10473,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
> >         if (!prog)
> >                 return;
> >
> > -       WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
> >         event->prog = NULL;
> >         bpf_prog_put(prog);
> >  }
> > @@ -11928,13 +11932,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> >                 overflow_handler = parent_event->overflow_handler;
> >                 context = parent_event->overflow_handler_context;
> >  #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
> > -               if (overflow_handler == bpf_overflow_handler) {
> > +               if (parent_event->prog) {
> >                         struct bpf_prog *prog = parent_event->prog;
> >
> >                         bpf_prog_inc(prog);
> >                         event->prog = prog;
> > -                       event->orig_overflow_handler =
> > -                               parent_event->orig_overflow_handler;
> >                 }
> >  #endif
> >         }
> > --
> > 2.34.1
> >