[PATCH v6] Cygwin: pipe: Avoid deadlock for non-cygwin writer.

[Takashi Yano <takashi.yano@nifty.ne.jp>]

- As mentioned in commit message of the commit b531d6b0, if multiple
  writers including non-cygwin app exist, the non-cygwin app cannot
  detect pipe closure on the read side when the pipe is created by
  system account or the the pipe creator is running as service.
  This is because query_hdl which is held in write side also is a
  read end of the pipe, so the pipe is still alive for the non-cygwin
  app even after the reader is closed.

  To avoid this problem, this patch lets all processes in the same
  process group close query_hdl using newly introduced internal signal
  __SIGNONCYGCHLD when non-cygwin app is started.

  Addresses: https://cygwin.com/pipermail/cygwin/2022-March/251097.html
---
 winsup/cygwin/fhandler.h       | 20 ++++++++++++++++++++
 winsup/cygwin/fhandler_pipe.cc | 23 +++++++++++++++++++++++
 winsup/cygwin/sigproc.cc       | 10 ++++++++++
 winsup/cygwin/sigproc.h        |  1 +
 winsup/cygwin/spawn.cc         | 18 +++++++++++++++++-
 5 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index b87160edb..80dd94508 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -1194,6 +1194,7 @@ private:
   HANDLE hdl_cnt_mtx;
   HANDLE query_hdl_proc;
   HANDLE query_hdl_value;
+  HANDLE query_hdl_close_req_evt;
   uint64_t pipename_key;
   DWORD pipename_pid;
   LONG pipename_id;
@@ -1255,9 +1256,28 @@ public:
 	CloseHandle (query_hdl);
 	query_hdl = NULL;
       }
+    if (query_hdl_close_req_evt)
+      {
+	CloseHandle (query_hdl_close_req_evt);
+	query_hdl_close_req_evt = NULL;
+      }
   }
   bool reader_closed ();
   HANDLE temporary_query_hdl ();
+  bool need_close_query_hdl ()
+    {
+      return query_hdl_close_req_evt ?
+	IsEventSignalled (query_hdl_close_req_evt) : false;
+    }
+  bool request_close_query_hdl ()
+    {
+      if (query_hdl_close_req_evt)
+	{
+	  SetEvent (query_hdl_close_req_evt);
+	  return true;
+	}
+      return false;
+    }
 };
 
 #define CYGWIN_FIFO_PIPE_NAME_LEN     47
diff --git a/winsup/cygwin/fhandler_pipe.cc b/winsup/cygwin/fhandler_pipe.cc
index aef0bf6be..270ba34a0 100644
--- a/winsup/cygwin/fhandler_pipe.cc
+++ b/winsup/cygwin/fhandler_pipe.cc
@@ -566,6 +566,8 @@ fhandler_pipe::fixup_after_fork (HANDLE parent)
     fork_fixup (parent, select_sem, "select_sem");
   if (query_hdl)
     fork_fixup (parent, query_hdl, "query_hdl");
+  if (query_hdl_close_req_evt)
+    fork_fixup (parent, query_hdl_close_req_evt, "query_hdl_close_req_evt");
 
   fhandler_base::fixup_after_fork (parent);
   ReleaseMutex (hdl_cnt_mtx);
@@ -616,6 +618,16 @@ fhandler_pipe::dup (fhandler_base *child, int flags)
       ftp->close ();
       res = -1;
     }
+  else if (query_hdl_close_req_evt &&
+	   !DuplicateHandle (GetCurrentProcess (), query_hdl_close_req_evt,
+			     GetCurrentProcess (),
+			     &ftp->query_hdl_close_req_evt,
+			     0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
+    {
+      __seterrno ();
+      ftp->close ();
+      res = -1;
+    }
   ReleaseMutex (hdl_cnt_mtx);
 
   debug_printf ("res %d", res);
@@ -635,6 +647,8 @@ fhandler_pipe::close ()
   WaitForSingleObject (hdl_cnt_mtx, INFINITE);
   if (query_hdl)
     CloseHandle (query_hdl);
+  if (query_hdl_close_req_evt)
+    CloseHandle (query_hdl_close_req_evt);
   int ret = fhandler_base::close ();
   ReleaseMutex (hdl_cnt_mtx);
   CloseHandle (hdl_cnt_mtx);
@@ -868,9 +882,18 @@ fhandler_pipe::create (fhandler_pipe *fhs[2], unsigned psize, int mode)
 			0, sa->bInheritHandle, DUPLICATE_SAME_ACCESS))
     goto err_close_hdl_cnt_mtx0;
 
+  if (fhs[1]->query_hdl)
+    {
+      fhs[1]->query_hdl_close_req_evt = CreateEvent (sa, TRUE, FALSE, NULL);
+      if (!fhs[1]->query_hdl_close_req_evt)
+	goto err_close_hdl_cnt_mtx1;
+    }
+
   res = 0;
   goto out;
 
+err_close_hdl_cnt_mtx1:
+  CloseHandle (fhs[1]->hdl_cnt_mtx);
 err_close_hdl_cnt_mtx0:
   CloseHandle (fhs[0]->hdl_cnt_mtx);
 err_close_query_hdl:
diff --git a/winsup/cygwin/sigproc.cc b/winsup/cygwin/sigproc.cc
index d3f2b0c6a..62df96652 100644
--- a/winsup/cygwin/sigproc.cc
+++ b/winsup/cygwin/sigproc.cc
@@ -1477,6 +1477,16 @@ wait_sig (VOID *)
 		clearwait = true;
 	    }
 	  break;
+	case __SIGNONCYGCHLD:
+	  cygheap_fdenum cfd (false);
+	  while (cfd.next () >= 0)
+	    if (cfd->get_dev () == FH_PIPEW)
+	      {
+		fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
+		if (pipe->need_close_query_hdl ())
+		  pipe->close_query_handle ();
+	      }
+	  break;
 	}
       if (clearwait && !have_execed)
 	proc_subproc (PROC_CLEARWAIT, 0);
diff --git a/winsup/cygwin/sigproc.h b/winsup/cygwin/sigproc.h
index 23287c85b..d037eaec3 100644
--- a/winsup/cygwin/sigproc.h
+++ b/winsup/cygwin/sigproc.h
@@ -24,6 +24,7 @@ enum
   __SIGSETPGRP	    = -(_NSIG + 9),
   __SIGTHREADEXIT   = -(_NSIG + 10),
   __SIGPENDINGALL   = -(_NSIG + 11),
+  __SIGNONCYGCHLD   = -(_NSIG + 12),
 };
 #endif
 
diff --git a/winsup/cygwin/spawn.cc b/winsup/cygwin/spawn.cc
index fb3d09d84..400457117 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -28,6 +28,7 @@ details. */
 #include "tls_pbuf.h"
 #include "winf.h"
 #include "ntdll.h"
+#include "shared_info.h"
 
 static const suffix_info exe_suffixes[] =
 {
@@ -631,6 +632,7 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
 
       if (!iscygwin ())
 	{
+	  bool need_send_sig = false;
 	  int fd;
 	  cygheap_fdenum cfd (false);
 	  while ((fd = cfd.next ()) >= 0)
@@ -645,14 +647,28 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
 		     && (fd == fileno_stdout || fd == fileno_stderr))
 	      {
 		fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
-		pipe->close_query_handle ();
 		pipe->set_pipe_non_blocking (false);
+		if (pipe->request_close_query_hdl ())
+		  need_send_sig = true;
 	      }
 	    else if (cfd->get_dev () == FH_PIPER && fd == fileno_stdin)
 	      {
 		fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
 		pipe->set_pipe_non_blocking (false);
 	      }
+
+	  if (need_send_sig)
+	    {
+	      tty_min dummy_tty;
+	      dummy_tty.ntty = (fh_devices) myself->ctty;
+	      dummy_tty.pgid = myself->pgid;
+	      tty_min *t = cygwin_shared->tty.get_cttyp ();
+	      if (!t) /* If tty is not allocated, use dummy_tty instead. */
+		t = &dummy_tty;
+	      /* Emit __SIGNONCYGCHLD to let all processes in the
+		 process group close query_hdl. */
+	      t->kill_pgrp (__SIGNONCYGCHLD);
+	    }
 	}
 
       bool stdin_is_ptys = false;
-- 
2.35.1