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From: Takashi Yano <tyan0@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] Cygwin: pty: Stop closing and recreating attach_mutex. Date: Fri, 14 Jan 2022 14:14:58 +0000 (GMT) [thread overview] Message-ID: <20220114141458.CD5673835C16@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=3af461092e7ee9b76f3a1c18a6d95ed6e226df81 commit 3af461092e7ee9b76f3a1c18a6d95ed6e226df81 Author: Takashi Yano <takashi.yano@nifty.ne.jp> Date: Thu Jan 13 19:44:43 2022 +0900 Cygwin: pty: Stop closing and recreating attach_mutex. - Closing attach_mutex and recreating it causes the race issue between pty and console codes. With this patch, attach_mutex is created only once in a process which opens pty, and never closed in order to avoid this issue. Addresses: https://cygwin.com/pipermail/cygwin-developers/2021-December/012548.html Diff: --- winsup/cygwin/fhandler.h | 3 +++ winsup/cygwin/fhandler_console.cc | 17 ----------------- winsup/cygwin/fhandler_tty.cc | 30 ++++++++++++++++++++---------- winsup/cygwin/select.cc | 16 ---------------- 4 files changed, 23 insertions(+), 43 deletions(-) diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h index 4f70c4c0b..0cea1b7f3 100644 --- a/winsup/cygwin/fhandler.h +++ b/winsup/cygwin/fhandler.h @@ -1881,6 +1881,9 @@ class fhandler_serial: public fhandler_base #define release_output_mutex() \ __release_output_mutex (__PRETTY_FUNCTION__, __LINE__) +DWORD acquire_attach_mutex (DWORD t); +void release_attach_mutex (void); + class tty; class tty_min; class fhandler_termios: public fhandler_base diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc index 024be522b..0e4b41559 100644 --- a/winsup/cygwin/fhandler_console.cc +++ b/winsup/cygwin/fhandler_console.cc @@ -56,25 +56,8 @@ fhandler_console::console_state NO_COPY *fhandler_console::shared_console_info; bool NO_COPY fhandler_console::invisible_console; -/* Mutex for AttachConsole()/FreeConsole() in fhandler_tty.cc */ -HANDLE attach_mutex; - extern DWORD mutex_timeout; /* defined in fhandler_termios.cc */ -static inline void -acquire_attach_mutex (DWORD t) -{ - if (attach_mutex) - WaitForSingleObject (attach_mutex, t); -} - -static inline void -release_attach_mutex () -{ - if (attach_mutex) - ReleaseMutex (attach_mutex); -} - /* con_ra is shared in the same process. Only one console can exist in a process, therefore, static is suitable. */ static struct fhandler_base::rabuf_t con_ra; diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc index f68e80df9..1ae4edd63 100644 --- a/winsup/cygwin/fhandler_tty.cc +++ b/winsup/cygwin/fhandler_tty.cc @@ -58,8 +58,21 @@ struct pipe_reply { DWORD error; }; -extern HANDLE attach_mutex; /* Defined in fhandler_console.cc */ -static LONG master_cnt = 0; +HANDLE attach_mutex; + +DWORD acquire_attach_mutex (DWORD t) +{ + if (!attach_mutex) + return WAIT_OBJECT_0; + return WaitForSingleObject (attach_mutex, t); +} + +void release_attach_mutex (void) +{ + if (!attach_mutex) + return; + ReleaseMutex (attach_mutex); +} inline static bool pcon_pid_alive (DWORD pid); @@ -523,13 +536,13 @@ fhandler_pty_master::accept_input () { /* Slave attaches to a different console than master. Therefore reattach here. */ - WaitForSingleObject (attach_mutex, mutex_timeout); + acquire_attach_mutex (mutex_timeout); FreeConsole (); AttachConsole (target_pid); cp_to = GetConsoleCP (); FreeConsole (); AttachConsole (resume_pid); - ReleaseMutex (attach_mutex); + release_attach_mutex (); } else cp_to = GetConsoleCP (); @@ -2111,8 +2124,6 @@ fhandler_pty_master::close () master_fwd_thread->detach (); } } - if (InterlockedDecrement (&master_cnt) == 0) - CloseHandle (attach_mutex); /* Check if the last master handle has been closed. If so, set input_available_event to wake up potentially waiting slaves. */ @@ -2838,13 +2849,13 @@ fhandler_pty_master::pty_master_fwd_thread (const master_fwd_thread_param_t *p) { /* Slave attaches to a different console than master. Therefore reattach here. */ - WaitForSingleObject (attach_mutex, mutex_timeout); + acquire_attach_mutex (mutex_timeout); FreeConsole (); AttachConsole (target_pid); cp_from = GetConsoleOutputCP (); FreeConsole (); AttachConsole (resume_pid); - ReleaseMutex (attach_mutex); + release_attach_mutex (); } else cp_from = GetConsoleOutputCP (); @@ -2993,7 +3004,7 @@ fhandler_pty_master::setup () if (!(pcon_mutex = CreateMutex (&sa, FALSE, buf))) goto err; - if (InterlockedIncrement (&master_cnt) == 1) + if (!attach_mutex) attach_mutex = CreateMutex (&sa, FALSE, NULL); /* Create master control pipe which allows the master to duplicate @@ -3057,7 +3068,6 @@ err: close_maybe (input_available_event); close_maybe (output_mutex); close_maybe (input_mutex); - close_maybe (attach_mutex); close_maybe (from_master_nat); close_maybe (from_master); close_maybe (to_master_nat); diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index 0cd62d932..5b8fc0f81 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -1095,22 +1095,6 @@ fhandler_fifo::select_except (select_stuff *ss) return s; } -extern HANDLE attach_mutex; /* Defined in fhandler_console.cc */ - -static inline void -acquire_attach_mutex (DWORD t) -{ - if (attach_mutex) - WaitForSingleObject (attach_mutex, t); -} - -static inline void -release_attach_mutex () -{ - if (attach_mutex) - ReleaseMutex (attach_mutex); -} - extern DWORD mutex_timeout; /* defined in fhandler_termios.cc */ static int
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