commit f18803427541f34082fd659a4dd0deb49a8a4b89
author Yabin Cui <yabinc@google.com> Thu Feb 27 17:11:58 2020 -0800
committer Yabin Cui <yabinc@google.com> Fri Feb 28 10:14:21 2020 -0800
tree 2da7610edef803d71f05bc3d0301516885a40120
parent 0941edfb7ed31cea4a27334377b87746352edec8

time_in_state: don't block sched_switch events.

Returning zero in sched_switch bpf program blocks userspace
from receiving sched_switch events from perf_event_fd interface.

Bug: 149797433
Test: build and boot.

Change-Id: Icea311d6fe05d2698a624d17d47141fc735681de

time_in_state.c

diff --git a/time_in_state.c b/time_in_state.c
index cb56a93..5befc6d 100644
--- a/time_in_state.c
+++ b/time_in_state.c
@@ -45,23 +45,24 @@
 
 DEFINE_BPF_PROG("tracepoint/sched/sched_switch", AID_ROOT, AID_SYSTEM, tp_sched_switch)
 (struct switch_args* args) {
+    const int ALLOW = 1;  // return 1 to avoid blocking simpleperf from receiving events.
     uint32_t zero = 0;
     uint64_t* last = bpf_cpu_last_update_map_lookup_elem(&zero);
-    if (!last) return 0;
+    if (!last) return ALLOW;
     uint64_t old_last = *last;
     uint64_t time = bpf_ktime_get_ns();
     *last = time;
 
     uint32_t* active = bpf_nr_active_map_lookup_elem(&zero);
-    if (!active) return 0;
+    if (!active) return ALLOW;
 
     uint32_t cpu = bpf_get_smp_processor_id();
     uint32_t* policyp = bpf_cpu_policy_map_lookup_elem(&cpu);
-    if (!policyp) return 0;
+    if (!policyp) return ALLOW;
     uint32_t policy = *policyp;
 
     uint32_t* policy_active = bpf_policy_nr_active_map_lookup_elem(&policy);
-    if (!policy_active) return 0;
+    if (!policy_active) return ALLOW;
 
     uint32_t nactive = *active - 1;
     uint32_t policy_nactive = *policy_active - 1;
@@ -77,7 +78,7 @@
     // 2) old_last == 0, so this is the first time we've seen this CPU. Any delta will be invalid,
     //    and our active CPU counts don't include this CPU yet so we shouldn't decrement them even
     //    if we're going idle.
-    if (!args->prev_pid || !old_last) return 0;
+    if (!args->prev_pid || !old_last) return ALLOW;
 
     if (!args->next_pid) {
         __sync_fetch_and_add(active, -1);
@@ -85,7 +86,7 @@
     }
 
     uint8_t* freq_idxp = bpf_policy_freq_idx_map_lookup_elem(&policy);
-    if (!freq_idxp || !*freq_idxp) return 0;
+    if (!freq_idxp || !*freq_idxp) return ALLOW;
     // freq_to_idx_map uses 1 as its minimum index so that *freq_idxp == 0 only when uninitialized
     uint8_t freq_idx = *freq_idxp - 1;
 
@@ -125,7 +126,7 @@
     } else {
         bpf_uid_last_update_map_update_elem(&uid, &time, BPF_NOEXIST);
     }
-    return 0;
+    return ALLOW;
 }
 
 struct cpufreq_args {