Don't use vfork() before clone()

I'm seeing hangs in Glibc's setxid_mark_thread() again. This is
probably because the use of an intermediate process to make clone()
safe from a multi-threaded program (see
524f89f1399724e596f61faba2c6861b1bb7b9c5) is defeated by the use of
vfork(), since the intermediate process will have a copy of Glibc's
threading data structures due to the vfork(). So use a regular fork()
again.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 506eb633aae8..d0299914813c 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1992,6 +1992,8 @@ void DerivationGoal::startBuilder()
            CLONE_PARENT to ensure that the real builder is parented to
            us.
         */
+        ProcessOptions options;
+        options.allowVfork = false;
         Pid helper = startProcess([&]() {
             char stack[32 * 1024];
             int flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | CLONE_NEWUTS | CLONE_PARENT | SIGCHLD;
@@ -2004,7 +2006,7 @@ void DerivationGoal::startBuilder()
             if (child == -1) throw SysError("cloning builder process");
             writeFull(builderOut.writeSide, int2String(child) + "\n");
             _exit(0);
-        });
+        }, options);
         if (helper.wait(true) != 0)
             throw Error("unable to start build process");
         pid_t tmp;