logd: best 2/3 filter for timezone glitches
klogd is sensitive to changes in timezone resulting in glitches
surrounding conversion to local realtime logging. logger manages
a map from monotonic to realtime, but the process is racey since
the system can change the timezone at any time, this catches those
cases where it glitches.
Bug: 21868540
Change-Id: I03de6675fcd04f18ba7306a24dc3d9e750d86976
diff --git a/logd/LogKlog.cpp b/logd/LogKlog.cpp
index 2a3f52f..db7e682 100644
--- a/logd/LogKlog.cpp
+++ b/logd/LogKlog.cpp
@@ -778,6 +778,31 @@
memcpy(np, p, b);
np[b] = '\0';
+ if (!isMonotonic()) {
+ // Watch out for singular race conditions with timezone causing near
+ // integer quarter-hour jumps in the time and compensate accordingly.
+ // Entries will be temporal within near_seconds * 2. b/21868540
+ static uint32_t vote_time[3];
+ vote_time[2] = vote_time[1];
+ vote_time[1] = vote_time[0];
+ vote_time[0] = now.tv_sec;
+
+ if (vote_time[1] && vote_time[2]) {
+ static const unsigned near_seconds = 10;
+ static const unsigned timezones_seconds = 900;
+ int diff0 = (vote_time[0] - vote_time[1]) / near_seconds;
+ unsigned abs0 = (diff0 < 0) ? -diff0 : diff0;
+ int diff1 = (vote_time[1] - vote_time[2]) / near_seconds;
+ unsigned abs1 = (diff1 < 0) ? -diff1 : diff1;
+ if ((abs1 <= 1) && // last two were in agreement on timezone
+ ((abs0 + 1) % (timezones_seconds / near_seconds)) <= 2) {
+ abs0 = (abs0 + 1) / (timezones_seconds / near_seconds) *
+ timezones_seconds;
+ now.tv_sec -= (diff0 < 0) ? -abs0 : abs0;
+ }
+ }
+ }
+
// Log message
int rc = logbuf->log(LOG_ID_KERNEL, now, uid, pid, tid, newstr,
(unsigned short) n);