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Commit 8a2a2d18 authored by Josh Gao's avatar Josh Gao
Browse files

crash_dump: defer pausing threads until we're ready. 

Don't pause the threads we're going to dump until after we're about to
fetch their backtraces.

Bug: http://b/62112103
Test: debuggerd_test
Change-Id: Id7ab0464842b35f98f3b3ebc42fb76161d8afbd2
parent 8bb03907

debuggerd/Android.bp

+1 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ cc_defaults { 
        "-Wno-nullability-completeness",

        "-Os",

    ],

    cpp_std: "experimental",



    local_include_dirs: ["include"],

}

debuggerd/crash_dump.cpp

+30 −26
Original line number Diff line number Diff line
@@ -95,11 +95,6 @@ static bool ptrace_seize_thread(int pid_proc_fd, pid_t tid, std::string* error) 
    return false;

  }



  // Put the task into ptrace-stop state.

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

    PLOG(FATAL) << "failed to interrupt thread " << tid;

  }



  return true;

}
@@ -284,19 +279,22 @@ int main(int argc, char** argv) { 
  // Die if we take too long.

  alarm(2);



  std::string process_name = get_process_name(main_tid);

  std::string attach_error;



  std::map<pid_t, std::string> threads;



  {

    ATRACE_NAME("ptrace");

    ATRACE_NAME("ptrace_interrupt");



    // Seize the main thread.

    if (!ptrace_seize_thread(target_proc_fd, main_tid, &attach_error)) {

      LOG(FATAL) << attach_error;

    }



    // Seize the siblings.

    {

    threads.emplace(main_tid, get_thread_name(main_tid));



    // Seize its siblings.

    std::set<pid_t> siblings;

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

      PLOG(FATAL) << "failed to get process siblings";
@@ -310,10 +308,9 @@ int main(int argc, char** argv) { 
    for (pid_t sibling_tid : siblings) {

      if (!ptrace_seize_thread(target_proc_fd, sibling_tid, &attach_error)) {

        LOG(WARNING) << attach_error;

        } else {

          threads.emplace(sibling_tid, get_thread_name(sibling_tid));

        }

        continue;

      }

      threads.emplace(sibling_tid, get_thread_name(sibling_tid));

    }

  }
@@ -334,9 +331,6 @@ int main(int argc, char** argv) { 
    populate_open_files_list(target, &open_files);

  }



  std::string process_name = get_process_name(main_tid);

  threads.emplace(main_tid, get_thread_name(main_tid));



  // Drop our capabilities now that we've attached to the threads we care about.

  drop_capabilities();
@@ -347,6 +341,16 @@ int main(int argc, char** argv) { 
    tombstoned_connected = tombstoned_connect(target, &tombstoned_socket, &output_fd, dump_type_enum);

  }



  // Pause the threads.

  {

    ATRACE_NAME("ptrace_interrupt");

    for (const auto& [sibling_tid, _] : threads) {

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

        PLOG(FATAL) << "failed to interrupt thread " << sibling_tid;

      }

    }

  }



  // Write a '\1' to stdout to tell the crashing process to resume.

  // It also restores the value of PR_SET_DUMPABLE at this point.

  if (TEMP_FAILURE_RETRY(write(STDOUT_FILENO, "\1", 1)) == -1) {