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Commit 7c6e3133 authored by Josh Gao's avatar Josh Gao
Browse files

crash_dump: set a watchdog timer. 

PTRACE_DETACH is only necessary if the process is in group-stop state,
the tracer exiting is sufficient to detach and resume tracees.

Using this, set a 5 second timer with alarm(2) that just kills us, to
avoid leaving processes stopped.

Bug: http://b/34472671
Test: debuggerd_test
Test: crasher + manually inserting a 10 second sleep into crash_dump
Change-Id: Iacaa796f79037aa1585f3f2159abe45ef0069311
parent 122479f4

debuggerd/crash_dump.cpp

+28 −27
Original line number Diff line number Diff line
@@ -257,6 +257,9 @@ int main(int argc, char** argv) { 
    exit(0);

  }



  // Die if we take too long.

  alarm(20);



  check_process(target_proc_fd, target);



  std::string attach_error;
@@ -316,10 +319,9 @@ int main(int argc, char** argv) { 
  // Now that we have the signal that kicked things off, attach all of the

  // sibling threads, and then proceed.

  bool fatal_signal = signo != DEBUGGER_SIGNAL;

  int resume_signal = fatal_signal ? signo : 0;

  std::set<pid_t> siblings;

  std::set<pid_t> attached_siblings;

  if (resume_signal == 0) {

  if (fatal_signal) {

    if (!android::procinfo::GetProcessTids(target, &siblings)) {

      PLOG(FATAL) << "failed to get process siblings";

    }
@@ -352,12 +354,29 @@ int main(int argc, char** argv) { 
                      attached_siblings, abort_address, fatal_signal ? &amfd_data : nullptr);

  }



  // We don't actually need to PTRACE_DETACH, as long as our tracees aren't in

  // group-stop state, which is true as long as no stopping signals are sent.



  bool wait_for_gdb = android::base::GetBoolProperty("debug.debuggerd.wait_for_gdb", false);

  if (wait_for_gdb) {

  if (!fatal_signal || siginfo.si_code == SI_USER) {

    // Don't wait_for_gdb when the process didn't actually crash.

    if (!fatal_signal) {

    wait_for_gdb = false;

    } else {

  }



  // If the process crashed or we need to send it SIGSTOP for wait_for_gdb,

  // get it in a state where it can receive signals, and then send the relevant

  // signal.

  if (wait_for_gdb || fatal_signal) {

    if (ptrace(PTRACE_INTERRUPT, main_tid, 0, 0) != 0) {

      PLOG(ERROR) << "failed to use PTRACE_INTERRUPT on " << main_tid;

    }



    if (tgkill(target, main_tid, wait_for_gdb ? SIGSTOP : signo) != 0) {

      PLOG(ERROR) << "failed to resend signal " << signo << " to " << main_tid;

    }

  }



  if (wait_for_gdb) {

    // Use ALOGI to line up with output from engrave_tombstone.

    ALOGI(

      "***********************************************************\n"
@@ -369,24 +388,6 @@ int main(int argc, char** argv) { 
      "***********************************************************",

      target, main_tid);

  }

  }



  for (pid_t tid : attached_siblings) {

    // Don't send the signal to sibling threads.

    if (ptrace(PTRACE_DETACH, tid, 0, wait_for_gdb ? SIGSTOP : 0) != 0) {

      PLOG(ERROR) << "ptrace detach from " << tid << " failed";

    }

  }



  if (ptrace(PTRACE_DETACH, main_tid, 0, wait_for_gdb ? SIGSTOP : resume_signal)) {

    PLOG(ERROR) << "ptrace detach from main thread " << main_tid << " failed";

  }



  if (wait_for_gdb) {

    if (tgkill(target, main_tid, resume_signal) != 0) {

      PLOG(ERROR) << "failed to resend signal to process " << target;

    }

  }



  if (fatal_signal) {

    activity_manager_notify(target, signo, amfd_data);

debuggerd/debuggerd_test.cpp

+3 −12
Original line number Diff line number Diff line
@@ -340,24 +340,15 @@ TEST_F(CrasherTest, wait_for_gdb) { 
  AssertDeath(SIGABRT);

}



// wait_for_gdb shouldn't trigger on manually sent signals.

TEST_F(CrasherTest, wait_for_gdb_signal) {

  if (!android::base::SetProperty(kWaitForGdbKey, "1")) {

    FAIL() << "failed to enable wait_for_gdb";

  }



  StartCrasher("abort");

  ASSERT_EQ(0, kill(crasher_pid, SIGABRT)) << strerror(errno);



  std::this_thread::sleep_for(500ms);



  int status;

  ASSERT_EQ(crasher_pid, (TIMEOUT(1, waitpid(crasher_pid, &status, WUNTRACED))));

  ASSERT_TRUE(WIFSTOPPED(status));

  ASSERT_EQ(SIGSTOP, WSTOPSIG(status));



  ASSERT_EQ(0, kill(crasher_pid, SIGCONT)) << strerror(errno);



  AssertDeath(SIGABRT);

  ASSERT_EQ(0, kill(crasher_pid, SIGSEGV)) << strerror(errno);

  AssertDeath(SIGSEGV);

}



TEST_F(CrasherTest, backtrace) {