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])
> {
--
Takashi Yano <[email protected]>
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