From dbc1cae5c50e358fa820fd3bff41e0990943054f Mon Sep 17 00:00:00 2001
From: Corinna Vinschen <corinna@vinschen.de>
Date: Mon, 24 Aug 2015 18:37:53 +0200
Subject: [PATCH] Fix hang stracing forking processes but not following child

        * ntdll.h (PROCESSINFOCLASS): Define ProcessDebugFlags.
        * sigproc.cc (child_info::child_info): Only propagate _CI_STRACED to
        child if strace is actually tracing child processes.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
---
 winsup/cygwin/ChangeLog     |  6 ++++++
 winsup/cygwin/ntdll.h       |  3 ++-
 winsup/cygwin/release/2.2.2 | 14 ++++++++++++++
 winsup/cygwin/sigproc.cc    | 16 +++++++++++++++-
 4 files changed, 37 insertions(+), 2 deletions(-)
 create mode 100644 winsup/cygwin/release/2.2.2

diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index e6b222322..1ec6c714b 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,9 @@
+2015-08-24  Corinna Vinschen  <corinna@vinschen.de>
+
+	* ntdll.h (PROCESSINFOCLASS): Define ProcessDebugFlags.
+	* sigproc.cc (child_info::child_info): Only propagate _CI_STRACED to
+	child if strace is actually tracing child processes.
+
 2015-08-24  Corinna Vinschen  <corinna@vinschen.de>
 
 	* include/cygwin/version.h (CYGWIN_VERSION_DLL_MINOR): Bump to 2.
diff --git a/winsup/cygwin/ntdll.h b/winsup/cygwin/ntdll.h
index 8088e40a2..13a131deb 100644
--- a/winsup/cygwin/ntdll.h
+++ b/winsup/cygwin/ntdll.h
@@ -532,7 +532,8 @@ typedef enum _PROCESSINFOCLASS
   ProcessTimes = 4,
   ProcessSessionInformation = 24,
   ProcessWow64Information = 26,
-  ProcessImageFileName = 27
+  ProcessImageFileName = 27,
+  ProcessDebugFlags = 31
 } PROCESSINFOCLASS;
 
 /* Checked on 64 bit. */
diff --git a/winsup/cygwin/release/2.2.2 b/winsup/cygwin/release/2.2.2
new file mode 100644
index 000000000..eb2162b1e
--- /dev/null
+++ b/winsup/cygwin/release/2.2.2
@@ -0,0 +1,14 @@
+What's new:
+-----------
+
+
+What changed:
+-------------
+
+
+Bug Fixes
+---------
+
+- Fix a hang when stracing a forking or spawning process without activating
+  stracing of child processes.
+  Addresses: https://cygwin.com/ml/cygwin/2015-08/msg00390.html
diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index 12f61d2fb..13392504b 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -772,7 +772,21 @@ child_info::child_info (unsigned in_cb, child_info_types chtype,
   fhandler_union_cb = sizeof (fhandler_union);
   user_h = cygwin_user_h;
   if (strace.active ())
-    flag |= _CI_STRACED;
+    {
+      NTSTATUS status;
+      ULONG DebugFlags;
+
+      /* Only propagate _CI_STRACED to child if strace is actually tracing
+	 child processes of this process.  The undocumented ProcessDebugFlags
+	 returns 0 if EPROCESS->NoDebugInherit is TRUE, 1 otherwise.
+	 This avoids a hang when stracing a forking or spawning process
+	 with the -f flag set to "don't follow fork". */
+      status = NtQueryInformationProcess (GetCurrentProcess (),
+					  ProcessDebugFlags, &DebugFlags,
+					  sizeof (DebugFlags), NULL);
+      if (NT_SUCCESS (status) && DebugFlags)
+	flag |= _CI_STRACED;
+    }
   if (need_subproc_ready)
     {
       subproc_ready = CreateEvent (&sec_all, FALSE, FALSE, NULL);