[PATCH] Cygwin: pty: Fix master closing error regarding attach_mutex.

[Ken Brown]

On 10/8/2021 12:28 PM, Takashi Yano wrote:
> - If two or more pty masters are opened in a process, closing master
>    causes error when closing attach_mutex. This patch fixes the issue.
> 
> Addresses:
> https://cygwin.com/pipermail/cygwin-developers/2021-October/012418.html
> ---
>   winsup/cygwin/fhandler_tty.cc | 7 +++++--
>   winsup/cygwin/release/3.3.0   | 3 +++
>   2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc
> index 05fe5348a..823dabf73 100644
> --- a/winsup/cygwin/fhandler_tty.cc
> +++ b/winsup/cygwin/fhandler_tty.cc
> @@ -57,6 +57,7 @@ struct pipe_reply {
>   };
>   
>   extern HANDLE attach_mutex; /* Defined in fhandler_console.cc */
> +static LONG NO_COPY master_cnt = 0;
>   
>   inline static bool pcon_pid_alive (DWORD pid);
>   
> @@ -2041,7 +2042,8 @@ fhandler_pty_master::close ()
>   	    }
>   	  release_output_mutex ();
>   	  master_fwd_thread->terminate_thread ();
> -	  CloseHandle (attach_mutex);
> +	  if (InterlockedDecrement (&master_cnt) == 0)
> +	    CloseHandle (attach_mutex);
>   	}
>       }
>   
> @@ -2876,7 +2878,8 @@ fhandler_pty_master::setup ()
>     if (!(pcon_mutex = CreateMutex (&sa, FALSE, buf)))
>       goto err;
>   
> -  attach_mutex = CreateMutex (&sa, FALSE, NULL);
> +  if (InterlockedIncrement (&master_cnt) == 1)
> +    attach_mutex = CreateMutex (&sa, FALSE, NULL);
>   
>     /* Create master control pipe which allows the master to duplicate
>        the pty pipe handles to processes which deserve it. */
> diff --git a/winsup/cygwin/release/3.3.0 b/winsup/cygwin/release/3.3.0
> index 2f7340ac5..2df81a4ae 100644
> --- a/winsup/cygwin/release/3.3.0
> +++ b/winsup/cygwin/release/3.3.0
> @@ -71,3 +71,6 @@ Bug Fixes
>     in ps(1) output.
>     Addresses: https://cygwin.com/pipermail/cygwin/2021-July/248998.html
>                https://cygwin.com/pipermail/cygwin/2021-August/249124.html
> +
> +- Fix pty master closing error regarding attach_mutex.
> +  Addresses: https://cygwin.com/pipermail/cygwin-developers/2021-October/012418.html

Pushed.  Thanks.

Ken