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Subject[PATCH RFC 3/4] perf/core: Add support for SIGTRAP on perf events
From
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 */
+ 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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