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Commit fbc3a75e authored by Mark Salyzyn's avatar Mark Salyzyn
Browse files

llkd: make 100% sure process that triggers panic still exists 

There is time between inspection, filtration, determination and
dumping before triggering panic, make 100% sure the process still
exists.  If we had one false start, but another process triggers
and panic in the same pass, then recognize that we have already
dumped the data and skip it on the later ones.

Test: llkd unit test.
Bug: 33808187
Bug: 120378563
Bug: 120229612
Change-Id: Iacaf82a3d58e5a3c18edcff3c8fa540b21da36f1
parent 1fcf7f7d

llkd/libllkd.cpp

+12 −4
Original line number Diff line number Diff line
@@ -510,9 +510,7 @@ bool llkWriteStringToFileConfirm(const std::string& string, const std::string& f 
    return android::base::Trim(content) == string;

}



void llkPanicKernel(bool dump, pid_t tid, const char* state,

                    const std::string& message = "") __noreturn;

void llkPanicKernel(bool dump, pid_t tid, const char* state, const std::string& message) {

void llkPanicKernel(bool dump, pid_t tid, const char* state, const std::string& message = "") {

    if (!message.empty()) LOG(ERROR) << message;

    auto sysrqTriggerFd = llkFileToWriteFd("/proc/sysrq-trigger");

    if (sysrqTriggerFd < 0) {
@@ -521,6 +519,7 @@ void llkPanicKernel(bool dump, pid_t tid, const char* state, const std::string& 
        // The answer to life, the universe and everything

        ::exit(42);

        // NOTREACHED

        return;

    }

    ::sync();

    if (dump) {
@@ -544,6 +543,13 @@ void llkPanicKernel(bool dump, pid_t tid, const char* state, const std::string& 
    llkWriteStringToFile(message + (message.empty() ? "" : "\n") +

                                 "SysRq : Trigger a crash : 'livelock,"s + state + "'\n",

                         "/dev/kmsg");

    // Because panic is such a serious thing to do, let us

    // make sure that the tid being inspected still exists!

    auto piddir = procdir + std::to_string(tid) + "/stat";

    if (access(piddir.c_str(), F_OK) != 0) {

        PLOG(WARNING) << piddir;

        return;

    }

    android::base::WriteStringToFd("c", sysrqTriggerFd);

    // NOTREACHED

    // DYB
@@ -909,6 +915,7 @@ milliseconds llkCheck(bool checkRunning) { 
    ms -= llkCycle;

    auto myPid = ::getpid();

    auto myTid = ::gettid();

    auto dump = true;

    for (auto dp = llkTopDirectory.read(); dp != nullptr; dp = llkTopDirectory.read()) {

        std::string piddir;
@@ -1109,9 +1116,10 @@ milliseconds llkCheck(bool checkRunning) { 
            const auto message = state + " "s + llkFormat(procp->count) + " " +

                                 std::to_string(ppid) + "->" + std::to_string(pid) + "->" +

                                 std::to_string(tid) + " " + procp->getComm() + " [panic]";

            llkPanicKernel(true, tid,

            llkPanicKernel(dump, tid,

                           (state == 'Z') ? "zombie" : (state == 'D') ? "driver" : "sleeping",

                           message);

            dump = false;

        }

        LOG(VERBOSE) << "+closedir()";

    }