On Mon, 18 May 2026 10:13:26 +0900
Takashi Yano via Cygwin <[email protected]> wrote:
> On Mon, 18 May 2026 10:04:04 +0900
> Takashi Yano wrote:
> > On Thu, 14 May 2026 23:11:48 +0300
> > Ivan Krylov wrote:
> > > On Wed, 13 May 2026 12:59:59 +0300
> > > Ivan Krylov <[email protected]> wrote:
> > >
> > > > I think it doesn't close the race window completely.
> > >
> > > Here's a patch that I have more confidence in:
> > >
> > > diff --git a/winsup/cygwin/fhandler/console.cc
> > > b/winsup/cygwin/fhandler/console.cc
> > > index c76347f6f..a97df4cef 100644
> > > --- a/winsup/cygwin/fhandler/console.cc
> > > +++ b/winsup/cygwin/fhandler/console.cc
> > > @@ -62,6 +62,7 @@ fhandler_console::console_state NO_COPY
> > >
> > > static bool NO_COPY inside_pcon_checked = false;
> > > static bool NO_COPY inside_pcon = false;
> > > +static LONG NO_COPY inside_pcon_cleanup = 0;
> > > static int NO_COPY parent_pty;
> > > static HANDLE NO_COPY parent_pty_input_mutex = NULL;
> > >
> > > @@ -530,8 +531,13 @@ fhandler_console::cons_master_thread (handle_set_t
> > > *p, tty *ttyp)
> > > default: /* Error */
> > > free (input_rec);
> > > free (input_tmp);
> > > - if (inside_pcon && parent_pty_input_mutex)
> > > + if (inside_pcon && parent_pty_input_mutex) {
> > > ReleaseMutex (parent_pty_input_mutex);
> > > + if (InterlockedCompareExchange(&inside_pcon_cleanup, 0, 0)) {
> > > + ForceCloseHandle (parent_pty_input_mutex);
> > > + inside_pcon = false;
> > > + }
> > > + }
> > > ReleaseMutex (p->input_mutex);
> > > return;
> > > }
> > > @@ -713,8 +719,13 @@ remove_record:
> > > while (true);
> > > }
> > > skip_writeback:
> > > - if (inside_pcon && parent_pty_input_mutex)
> > > + if (inside_pcon && parent_pty_input_mutex) {
> > > ReleaseMutex (parent_pty_input_mutex);
> > > + if (InterlockedCompareExchange(&inside_pcon_cleanup, 0, 0)) {
> > > + ForceCloseHandle (parent_pty_input_mutex);
> > > + inside_pcon = false;
> > > + }
> > > + }
> > > ReleaseMutex (p->input_mutex);
> > > cygwait (40);
> > > }
> > > @@ -2048,7 +2059,7 @@ fhandler_console::pcon_hand_over_proc (void)
> > > else
> > > system_printf("Acquiring pcon_ho_mutex failed.");
> > > ReleaseMutex (mtx);
> > > - ForceCloseHandle (parent_pty_input_mutex);
> > > + InterlockedExchange(&inside_pcon_cleanup, 1);
> > > }
> > >
> > > bool
> > >
> > > Instead of manipulating the mutex handle shared between threads and
> > > leaving a race window between if(parent_pty_input_mutex) and
> > > WaitForSingleObject(parent_pty_input_mutex, ...), tell the
> > > cons_master_thread to close the handle and stop using it.
> >
> > Thanks for the report and the patch.
> >
> > The root cause of the problem is closing parent_pty_input_mutex before
> > stopping cons_master_thread.
> >
> > What abount just moving
> > > - ForceCloseHandle (parent_pty_input_mutex);
> > into fhandler_console::close() like:
> >
> > diff --git a/winsup/cygwin/fhandler/console.cc
> > b/winsup/cygwin/fhandler/console.cc
> > index c76347f6f..c4950885a 100644
> > --- a/winsup/cygwin/fhandler/console.cc
> > +++ b/winsup/cygwin/fhandler/console.cc
> > @@ -2048,7 +2048,6 @@ fhandler_console::pcon_hand_over_proc (void)
> > else
> > system_printf("Acquiring pcon_ho_mutex failed.");
> > ReleaseMutex (mtx);
> > - ForceCloseHandle (parent_pty_input_mutex);
> > }
> >
> > bool
> > @@ -2157,6 +2156,9 @@ fhandler_console::close (int flag)
> > CloseHandle (output_mutex);
> > output_mutex = NULL;
> >
> > + ForceCloseHandle (parent_pty_input_mutex);
>
> Hmm, this should be:
> + if (parent_pty_input_mutex)
> + CloseHandle (parent_pty_input_mutex);
>
> > + parent_pty_input_mutex = NULL;
> > +
> > WaitForSingleObject (shared_info_mutex, INFINITE);
> > if (--shared_info_state[unit] == 0 && shared_console_info[unit])
> > {
This might be better:
diff --git a/winsup/cygwin/fhandler/console.cc
b/winsup/cygwin/fhandler/console.cc
index c76347f6f..6fd4cd965 100644
--- a/winsup/cygwin/fhandler/console.cc
+++ b/winsup/cygwin/fhandler/console.cc
@@ -2018,7 +2018,6 @@ fhandler_console::setup_pcon_hand_over ()
if (get_console_process_id (owner, true, false, false, false))
{
inside_pcon = true;
- atexit (fhandler_console::pcon_hand_over_proc);
parent_pty = i;
parent_pty_input_mutex =
cygwin_shared->tty[i]->open_input_mutex (MAXIMUM_ALLOWED);
@@ -2157,6 +2156,8 @@ fhandler_console::close (int flag)
CloseHandle (output_mutex);
output_mutex = NULL;
+ pcon_hand_over_proc ();
+
WaitForSingleObject (shared_info_mutex, INFINITE);
if (--shared_info_state[unit] == 0 && shared_console_info[unit])
{
--
Takashi Yano <[email protected]>
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