Block signals while forking so they aren't run in the child process.

base/process/launch_posix.cc

Index: base/process/launch_posix.cc
diff --git a/base/process/launch_posix.cc b/base/process/launch_posix.cc
index 3708af6bac417b49e4015fed93eb49966ed78363..650744630a037e561d5670ad39d4171e4b5b83c3 100644
--- a/base/process/launch_posix.cc
+++ b/base/process/launch_posix.cc
@@ -77,23 +77,31 @@ void SetEnvironment(char** env) {
 #endif
 }
 
+// List of signals that we want to block while forking and then reset
+// to SIG_DFL in the child process.
+// The previous signal handlers are likely to be meaningless in the child's
+// context so we reset them to the defaults for now. http://crbug.com/44953
+// These signal handlers are set up at least in browser_main_posix.cc:
+// BrowserMainPartsPosix::PreEarlyInitialization and stack_trace_posix.cc:
+// EnableInProcessStackDumping.
+const int kSignalsToReset[] = {

[jln (very slow on Chromium), 2013/07/31 23:54:55]

This ignores the other implementation of ResetChildSignalHandlersToDefaults()
(where all signals get reset).

Maybe the solution is to write a function that iterates through all signal
numbers and blocks any signal with a custom signal handler and returns a mask
that will be restored in the parent after fork().

[mdempsky_google, 2013/08/01 00:31:57]

Uploaded a new patch that's slightly simpler and just blocks all signals while
fork()ing.  This seems okay to me since fork()ing isn't that common (I think?),
so it shouldn't cause any problems if other signals get delayed until after the
fork() completes.

(I also realized I need to restore the original sigmask in the child process
after calling ResetChildSignalHandlersToDefaults.)

+  SIGHUP,
+  SIGINT,
+  SIGILL,
+  SIGABRT,
+  SIGFPE,
+  SIGBUS,
+  SIGSEGV,
+  SIGSYS,
+  SIGTERM,
+};
+
 #if !defined(OS_LINUX) || \
     (!defined(__i386__) && !defined(__x86_64__) && !defined(__arm__))
 void ResetChildSignalHandlersToDefaults() {
-  // The previous signal handlers are likely to be meaningless in the child's
-  // context so we reset them to the defaults for now. http://crbug.com/44953
-  // These signal handlers are set up at least in browser_main_posix.cc:
-  // BrowserMainPartsPosix::PreEarlyInitialization and stack_trace_posix.cc:
-  // EnableInProcessStackDumping.
-  signal(SIGHUP, SIG_DFL);
-  signal(SIGINT, SIG_DFL);
-  signal(SIGILL, SIG_DFL);
-  signal(SIGABRT, SIG_DFL);
-  signal(SIGFPE, SIG_DFL);
-  signal(SIGBUS, SIG_DFL);
-  signal(SIGSEGV, SIG_DFL);
-  signal(SIGSYS, SIG_DFL);
-  signal(SIGTERM, SIG_DFL);
+  for (size_t i = 0; i < arraysize(kSignalsToReset); i++) {
+    signal(kSignalsToReset[i], SIG_DFL);
+  }
 }
 
 #else
@@ -394,6 +402,18 @@ bool LaunchProcess(const std::vector<std::string>& argv,
   if (options.environ)
     new_environ.reset(AlterEnvironment(*options.environ, GetEnvironment()));
 
+  sigset_t sigs_to_block;
+  sigemptyset(&sigs_to_block);
+  for (size_t i = 0; i < arraysize(kSignalsToReset); i++) {
+    sigaddset(&sigs_to_block, kSignalsToReset[i]);
+  }
+
+  sigset_t old_sigset;
+  if (pthread_sigmask(SIG_BLOCK, &sigs_to_block, &old_sigset) != 0) {
+    DPLOG(ERROR) << "pthread_sigmask";
+    return false;
+  }
+
   pid_t pid;
 #if defined(OS_LINUX)
   if (options.clone_flags) {
@@ -404,6 +424,12 @@ bool LaunchProcess(const std::vector<std::string>& argv,
     pid = fork();
   }
 
+  if (pid != 0) {
+    if (pthread_sigmask(SIG_SETMASK, &old_sigset, NULL) != 0) {
+      NOTREACHED();
+    }
+  }
+
   if (pid < 0) {
     DPLOG(ERROR) << "fork";
     return false;