public inbox for cygwin-patches@cygwin.com
 help / color / mirror / Atom feed
From: Takashi Yano <takashi.yano@nifty.ne.jp>
To: cygwin-patches@cygwin.com
Subject: [PATCH v4] Cygwin: pipe: Avoid deadlock for non-cygwin writer.
Date: Tue, 29 Mar 2022 18:07:53 +0900	[thread overview]
Message-ID: <20220329090753.47207-1-takashi.yano@nifty.ne.jp> (raw)

- 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       | 11 +++++++++++
 winsup/cygwin/fhandler_pipe.cc | 23 +++++++++++++++++++++++
 winsup/cygwin/sigproc.cc       | 10 ++++++++++
 winsup/cygwin/sigproc.h        |  1 +
 winsup/cygwin/spawn.cc         | 13 ++++++++++++-
 5 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index b87160edb..006c7b4bf 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;
@@ -1258,6 +1259,16 @@ public:
   }
   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;
+    }
+  void request_close_query_hdl ()
+    {
+      if (query_hdl_close_req_evt)
+	SetEvent (query_hdl_close_req_evt);
+    }
 };
 
 #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..cd2d3a7ef 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[] =
 {
@@ -645,8 +646,18 @@ 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);
+		pipe->request_close_query_hdl ();
+
+		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);
 	      }
 	    else if (cfd->get_dev () == FH_PIPER && fd == fileno_stdin)
 	      {
-- 
2.35.1


             reply	other threads:[~2022-03-29  9:08 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-29  9:07 Takashi Yano [this message]
2022-03-29 15:21 ` Jeremy Drake
2022-03-30  0:17   ` Takashi Yano
2022-04-01  8:44     ` Takashi Yano
2022-03-29 15:40 ` Jeremy Drake

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20220329090753.47207-1-takashi.yano@nifty.ne.jp \
    --to=takashi.yano@nifty.ne.jp \
    --cc=cygwin-patches@cygwin.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).