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);
+ 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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