From 8ea53fa87e63dac824c274216d84d7eda973805c Mon Sep 17 00:00:00 2001
From: Christopher Ferris <cferris@google.com>
Date: Wed, 28 Jan 2015 16:13:56 -0800
Subject: [PATCH] Only one crashing thread should contact debuggerd.

If two or more threads crash at the same time, only let one talk to
debuggerd. It's possible for a race to occur that two threads send
data to debuggerd, the second one will cause errors in debuggerd since
the process will die once debuggerd lets the crashing pid start again.

Bug: 19183955
Change-Id: I17dfce46102117ab4a870f7381bd526488d37fb5
---
 linker/debugger.cpp | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/linker/debugger.cpp b/linker/debugger.cpp
index c889544d1..6fe9524e7 100644
--- a/linker/debugger.cpp
+++ b/linker/debugger.cpp
@@ -30,9 +30,11 @@
 
 #include <errno.h>
 #include <inttypes.h>
+#include <pthread.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/prctl.h>
 #include <sys/socket.h>
@@ -212,6 +214,23 @@ static void send_debuggerd_packet(siginfo_t* info) {
     return;
   }
 
+  // Mutex to prevent multiple crashing threads from trying to talk
+  // to debuggerd at the same time.
+  static pthread_mutex_t crash_mutex = PTHREAD_MUTEX_INITIALIZER;
+  int ret = pthread_mutex_trylock(&crash_mutex);
+  if (ret != 0) {
+    if (ret == EBUSY) {
+      __libc_format_log(ANDROID_LOG_INFO, "libc",
+                        "Another thread has contacted debuggerd first, stop and wait for process to die.");
+      // This will never complete since the lock is never released.
+      pthread_mutex_lock(&crash_mutex);
+    } else {
+      __libc_format_log(ANDROID_LOG_INFO, "libc",
+                        "pthread_mutex_trylock failed: %s", strerror(ret));
+    }
+    return;
+  }
+
   int s = socket_abstract_client(DEBUGGER_SOCKET_NAME, SOCK_STREAM | SOCK_CLOEXEC);
   if (s == -1) {
     __libc_format_log(ANDROID_LOG_FATAL, "libc", "Unable to open connection to debuggerd: %s",
@@ -228,7 +247,7 @@ static void send_debuggerd_packet(siginfo_t* info) {
   msg.tid = gettid();
   msg.abort_msg_address = reinterpret_cast<uintptr_t>(g_abort_message);
   msg.original_si_code = (info != nullptr) ? info->si_code : 0;
-  int ret = TEMP_FAILURE_RETRY(write(s, &msg, sizeof(msg)));
+  ret = TEMP_FAILURE_RETRY(write(s, &msg, sizeof(msg)));
   if (ret == sizeof(msg)) {
     char debuggerd_ack;
     ret = TEMP_FAILURE_RETRY(read(s, &debuggerd_ack, 1));