perf/bpf: Always use perf callchains if exist

If the perf_event has PERF_SAMPLE_CALLCHAIN, BPF can use it for stack trace.
The problematic cases like PEBS and IBS already handled in the PMU driver and
they filled the callchain info in the sample data.  For others, we can call
perf_callchain() before the BPF handler.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220908214104.3851807-2-namhyung@kernel.org

kernel/bpf/stackmap.c

@@ -338,7 +338,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
 	int ret;
 
 	/* perf_sample_data doesn't have callchain, use bpf_get_stackid */
-	if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))
+	if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
 		return bpf_get_stackid((unsigned long)(ctx->regs),
 				       (unsigned long) map, flags, 0, 0);
 
@@ -506,7 +506,7 @@ BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
 	int err = -EINVAL;
 	__u64 nr_kernel;
 
-	if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))
+	if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN))
 		return __bpf_get_stack(regs, NULL, NULL, buf, size, flags);
 
 	if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |

kernel/events/core.c

@@ -10000,8 +10000,16 @@ static void bpf_overflow_handler(struct perf_event *event,
 		goto out;
 	rcu_read_lock();
 	prog = READ_ONCE(event->prog);
-	if (prog)
+	if (prog) {
+		if (prog->call_get_stack &&
+		    (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
+		    !(data->sample_flags & PERF_SAMPLE_CALLCHAIN)) {
+			data->callchain = perf_callchain(event, regs);
+			data->sample_flags |= PERF_SAMPLE_CALLCHAIN;
+		}
+
 		ret = bpf_prog_run(prog, &ctx);
+	}
 	rcu_read_unlock();
 out:
 	__this_cpu_dec(bpf_prog_active);
@@ -10027,7 +10035,7 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
 
 	if (event->attr.precise_ip &&
 	    prog->call_get_stack &&
-	    (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) ||
+	    (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) ||
 	     event->attr.exclude_callchain_kernel ||
 	     event->attr.exclude_callchain_user)) {
 		/*