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SubjectRe: [PATCH RFC 3/4] perf/core: Add support for SIGTRAP on perf events
On Tue, Feb 23, 2021 at 3:34 PM Marco Elver <elver@google.com> wrote:
>
> Adds bit perf_event_attr::sigtrap, which can be set to cause events to
> send SIGTRAP (with si_code TRAP_PERF) to the task where the event
> occurred. To distinguish perf events and allow user space to decode
> si_perf (if set), the event type is set in si_errno.
>
> The primary motivation is to support synchronous signals on perf events
> in the task where an event (such as breakpoints) triggered.
>
> Link: https://lore.kernel.org/lkml/YBv3rAT566k+6zjg@hirez.programming.kicks-ass.net/
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> include/uapi/linux/perf_event.h | 3 ++-
> kernel/events/core.c | 21 +++++++++++++++++++++
> 2 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index ad15e40d7f5d..b9cc6829a40c 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -389,7 +389,8 @@ struct perf_event_attr {
> cgroup : 1, /* include cgroup events */
> text_poke : 1, /* include text poke events */
> build_id : 1, /* use build id in mmap2 events */
> - __reserved_1 : 29;
> + sigtrap : 1, /* send synchronous SIGTRAP on event */
> + __reserved_1 : 28;
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 37a8297be164..8718763045fd 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6288,6 +6288,17 @@ void perf_event_wakeup(struct perf_event *event)
> }
> }
>
> +static void perf_sigtrap(struct perf_event *event)
> +{
> + struct kernel_siginfo info;
> +
> + clear_siginfo(&info);
> + info.si_signo = SIGTRAP;
> + info.si_code = TRAP_PERF;
> + info.si_errno = event->attr.type;
> + force_sig_info(&info);
> +}
> +
> static void perf_pending_event_disable(struct perf_event *event)
> {
> int cpu = READ_ONCE(event->pending_disable);
> @@ -6297,6 +6308,13 @@ static void perf_pending_event_disable(struct perf_event *event)
>
> if (cpu == smp_processor_id()) {
> WRITE_ONCE(event->pending_disable, -1);
> +
> + if (event->attr.sigtrap) {
> + atomic_inc(&event->event_limit); /* rearm event */

Can/should this be atomic_set(&event->event_limit, 1)? It should only
go between 1 and 0, right?
Otherwise:

Acked-by: Dmitry Vyukov <dvyukov@google.com>


> + perf_sigtrap(event);
> + return;
> + }
> +
> perf_event_disable_local(event);
> return;
> }
> @@ -11325,6 +11343,9 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
>
> event->state = PERF_EVENT_STATE_INACTIVE;
>
> + if (event->attr.sigtrap)
> + atomic_set(&event->event_limit, 1);
> +
> if (task) {
> event->attach_state = PERF_ATTACH_TASK;
> /*
> --
> 2.30.0.617.g56c4b15f3c-goog
>

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