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From: Takashi Yano <tyan0@sourceware.org> To: cygwin-cvs@sourceware.org Subject: [newlib-cygwin/cygwin-3_3-branch] Cygwin: pty: Prevent deadlock on echo output. Date: Sun, 13 Feb 2022 15:17:55 +0000 (GMT) [thread overview] Message-ID: <20220213151755.38AD13858023@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c00d44595801b98848bc27b3bf30b0b390df9e42 commit c00d44595801b98848bc27b3bf30b0b390df9e42 Author: Takashi Yano <takashi.yano@nifty.ne.jp> Date: Thu Feb 10 17:22:11 2022 +0900 Cygwin: pty: Prevent deadlock on echo output. - If the slave process writes a lot of text output, doecho() can cause deadlock. This is because output_mutex is held in slave:: write() and if WriteFile() is blocked due to pipe full, doecho() tries to acquire output_mutex and gets into deadlock. With this patch, the deadlock is prevented on the sacrifice of atomicity of doecho(). Diff: --- winsup/cygwin/fhandler_tty.cc | 2 -- 1 file changed, 2 deletions(-) diff --git a/winsup/cygwin/fhandler_tty.cc b/winsup/cygwin/fhandler_tty.cc index 7bef6958c..7e065c46a 100644 --- a/winsup/cygwin/fhandler_tty.cc +++ b/winsup/cygwin/fhandler_tty.cc @@ -496,11 +496,9 @@ void fhandler_pty_master::doecho (const void *str, DWORD len) { ssize_t towrite = len; - acquire_output_mutex (mutex_timeout); if (!process_opost_output (echo_w, str, towrite, true, get_ttyp (), is_nonblocking ())) termios_printf ("Write to echo pipe failed, %E"); - release_output_mutex (); } int
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