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Commit b06247d9 authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

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
parent ce4bbcfb

logd/LogKlog.cpp

+25 −0
Original line number Diff line number Diff line
@@ -778,6 +778,31 @@ int LogKlog::log(const char *buf, size_t len) { 
    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);