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Commit b64dd85c authored by Josh Gao's avatar Josh Gao
Browse files

debuggerd_handler: actually wait for pseudothread to exit. 

Occasionally, the pseudothread wouldn't exit in time after unlocking
the mutex to get crash_dump to proceed, resulting in spurious error
messages. Instead of using a mutex to emulate pthread_join, just
implement it correctly.

Bug: http://b/34472671
Test: debuggerd_test
Change-Id: I5c2658a84e9407ed8cc0ef2ad0fb648c388b7ad1
parent 13c15e05

debuggerd/handler/debuggerd_handler.cpp

+13 −9
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ 
#include <errno.h>

#include <fcntl.h>

#include <inttypes.h>

#include <linux/futex.h>

#include <pthread.h>

#include <sched.h>

#include <signal.h>
@@ -46,6 +47,7 @@ 
#include <sys/wait.h>

#include <unistd.h>



#include "private/bionic_futex.h"

#include "private/libc_logging.h"



// see man(2) prctl, specifically the section about PR_GET_NAME
@@ -151,7 +153,6 @@ static bool have_siginfo(int signum) { 
}



struct debugger_thread_info {

  pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

  bool crash_dump_started = false;

  pid_t crashing_tid;

  pid_t pseudothread_tid;
@@ -228,7 +229,7 @@ static int debuggerd_dispatch_pseudothread(void* arg) { 
    }

  }



  pthread_mutex_unlock(&thread_info->mutex);

  syscall(__NR_exit, 0);

  return 0;

}
@@ -267,23 +268,26 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) 
  }



  debugger_thread_info thread_info = {

    .pseudothread_tid = -1,

    .crashing_tid = gettid(),

    .signal_number = signal_number,

    .info = info

  };

  pthread_mutex_lock(&thread_info.mutex);



  // Essentially pthread_create without CLONE_FILES (see debuggerd_dispatch_pseudothread).

  pid_t child_pid = clone(debuggerd_dispatch_pseudothread, pseudothread_stack,

                          CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID,

  pid_t child_pid =

    clone(debuggerd_dispatch_pseudothread, pseudothread_stack,

          CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,

          &thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);

  if (child_pid == -1) {

    fatal("failed to spawn debuggerd dispatch thread: %s", strerror(errno));

  }



  // Wait for the child to finish and unlock the mutex.

  // This relies on bionic behavior that isn't guaranteed by the standard.

  pthread_mutex_lock(&thread_info.mutex);

  // Wait for the child to start...

  __futex_wait(&thread_info.pseudothread_tid, -1, nullptr);



  // and then wait for it to finish.

  __futex_wait(&thread_info.pseudothread_tid, child_pid, nullptr);



  // Signals can either be fatal or nonfatal.

  // For fatal signals, crash_dump will PTRACE_CONT us with the signal we