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From: Corinna Vinschen <corinna@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin] Cygwin: pty: Fix a race issue in startup of pseudo console. Date: Fri, 5 Mar 2021 15:12:02 +0000 (GMT) [thread overview] Message-ID: <20210305151202.686773848000@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=919dea66d3ca17eac4aa08d4156516feb165ec82 commit 919dea66d3ca17eac4aa08d4156516feb165ec82 Author: Takashi Yano via Cygwin-patches <cygwin-patches@cygwin.com> Date: Thu Mar 4 17:56:34 2021 +0900 Cygwin: pty: Fix a race issue in startup of pseudo console. - If two non-cygwin apps are started simultaneously and this is the first execution of non-cygwin apps in the pty, these occasionally hang up. The cause is the race issue between term_has_pcon_cap(), reset_switch_to_pcon() and setup_pseudoconsole(). This patch fixes the issue. Diff: --- winsup/cygwin/fhandler_tty.cc | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc index 3fcaa8277..930501d01 100644 --- a/winsup/cygwin/fhandler_tty.cc +++ b/winsup/cygwin/fhandler_tty.cc @@ -1118,15 +1118,20 @@ fhandler_pty_slave::reset_switch_to_pcon (void) } } } - if (get_ttyp ()->pcon_pid && get_ttyp ()->pcon_pid != myself->pid - && !!pinfo (get_ttyp ()->pcon_pid)) - /* There is a process which is grabbing pseudo console. */ - return; if (isHybrid) return; + WaitForSingleObject (pcon_mutex, INFINITE); + if (get_ttyp ()->pcon_pid && get_ttyp ()->pcon_pid != myself->pid + && !!pinfo (get_ttyp ()->pcon_pid)) + { + /* There is a process which is grabbing pseudo console. */ + ReleaseMutex (pcon_mutex); + return; + } get_ttyp ()->pcon_pid = 0; get_ttyp ()->switch_to_pcon_in = false; get_ttyp ()->pcon_activated = false; + ReleaseMutex (pcon_mutex); } ssize_t __stdcall @@ -3538,6 +3543,7 @@ fhandler_pty_slave::term_has_pcon_cap (const WCHAR *env) goto maybe_dumb; /* Check if terminal has CSI6n */ + WaitForSingleObject (pcon_mutex, INFINITE); WaitForSingleObject (input_mutex, INFINITE); /* Set pcon_activated and pcon_start so that the response will sent to io_handle rather than io_handle_cyg. */ @@ -3573,6 +3579,7 @@ fhandler_pty_slave::term_has_pcon_cap (const WCHAR *env) while (len); get_ttyp ()->pcon_activated = false; get_ttyp ()->pcon_pid = 0; + ReleaseMutex (pcon_mutex); if (len == 0) goto not_has_csi6n; @@ -3588,6 +3595,7 @@ not_has_csi6n: get_ttyp ()->pcon_start = false; get_ttyp ()->pcon_activated = false; ReleaseMutex (input_mutex); + ReleaseMutex (pcon_mutex); maybe_dumb: get_ttyp ()->pcon_cap_checked = true; return false;
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