possible race initializing pgid in spawned child

[Jeremy Drake]

I cannot duplicate this failure locally, but in GHA the following test
case fails with

Process group 0 != expected 704
child exited with code 1
FAIL winsup.api/spawnpgid.exe (exit status: 1)

I suspect there must be a race between the child process calling getpgid
and the parent running "vchild->pgid = myself->pgid" in sigproc.cc
proc_subproc PROC_ADD_CHILD.

---
 winsup/testsuite/Makefile.am            |  1 +
 winsup/testsuite/winsup.api/spawnpgid.c | 59 +++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 winsup/testsuite/winsup.api/spawnpgid.c

diff --git a/winsup/testsuite/Makefile.am b/winsup/testsuite/Makefile.am
index 67898f62a6..8f101695d5 100644
--- a/winsup/testsuite/Makefile.am
+++ b/winsup/testsuite/Makefile.am
@@ -48,6 +48,7 @@ check_PROGRAMS = \
 	winsup.api/shmtest \
 	winsup.api/sigchld \
 	winsup.api/signal-into-win32-api \
+	winsup.api/spawnpgid \
 	winsup.api/systemcall \
 	winsup.api/user_malloc \
 	winsup.api/waitpid \
diff --git a/winsup/testsuite/winsup.api/spawnpgid.c b/winsup/testsuite/winsup.api/spawnpgid.c
new file mode 100644
index 0000000000..214af9306d
--- /dev/null
+++ b/winsup/testsuite/winsup.api/spawnpgid.c
@@ -0,0 +1,59 @@
+#include <process.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int handle_child (char *arg)
+{
+  pid_t pgid = getpgid (0);
+  pid_t expectedpgid = atoi (arg);
+  if (!expectedpgid)
+    expectedpgid = getpid ();
+  if (pgid != expectedpgid)
+    {
+      fprintf (stderr, "Process group %d != expected %d\n", pgid, expectedpgid);
+      return 1;
+    }
+  return 0;
+}
+
+int main (int argc, char **argv)
+{
+  int status;
+  char buf[12];
+  const char * const childargv[] = {"pgroup", "--child", buf, NULL};
+
+  /* unbuffer stdout */
+  setvbuf(stdout, NULL, _IONBF, 0);
+
+  if (argc == 3 && !strcmp (argv[1], "--child"))
+    return handle_child (argv[2]);
+
+  /* ensure pgroup inherited by default */
+  sprintf (buf, "%d", getpgid (0));
+  status = spawnv (_P_WAIT, "/proc/self/exe", childargv);
+  if (status < 0)
+    {
+      perror ("spawnv");
+      return 1;
+    }
+  else if (WIFSIGNALED (status))
+    {
+      fprintf (stderr, "child termintated with signal %d\n", WTERMSIG (status));
+      return 1;
+    }
+  else if (WIFEXITED (status) && WEXITSTATUS (status) != 0)
+    {
+      fprintf (stderr, "child exited with code %d\n", WEXITSTATUS (status));
+      return 1;
+    }
+  else if (!WIFEXITED (status))
+    {
+      fprintf (stderr, "child terminated with status %x\n", status);
+      return 1;
+    }
+
+  return 0;
+}
-- 
2.49.0.windows.1