[PATCH 3/8] Cygwin: pty: Prevent deadlock on echo output.

Takashi Yano takashi.yano@nifty.ne.jp
Sun Feb 13 14:39:05 GMT 2022

- 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().
 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 ();

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