From 807708844979ba8c6d5717345a8608454992696d Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Thu, 16 Jul 2009 16:07:03 +0100 Subject: [PATCH] n_tty: Fix echo race If a tty in N_TTY mode with echo enabled manages to get itself into a state where - echo characters are pending - FASYNC is enabled - tty_write_wakeup is called from either - a device write path (pty) - an IRQ (serial) then it either deadlocks or explodes taking a mutex in the IRQ path. On the serial side it is almost impossible to reproduce because you have to go from a full serial port to a near empty one with echo characters pending. The pty case happens to have become possible to trigger using emacs and ptys, the pty changes having created a scenario which shows up this bug. The code path is n_tty:process_echoes() (takes mutex) tty_io:tty_put_char() pty:pty_write (or serial paths) tty_wakeup (from pty_write or serial IRQ) n_tty_write_wakeup() process_echoes() *KABOOM* Signed-off-by: Alan Cox Signed-off-by: Linus Torvalds --- drivers/char/n_tty.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c index 94a5d5020abc..ff47907ff1bf 100644 --- a/drivers/char/n_tty.c +++ b/drivers/char/n_tty.c @@ -1331,9 +1331,6 @@ handle_newline: static void n_tty_write_wakeup(struct tty_struct *tty) { - /* Write out any echoed characters that are still pending */ - process_echoes(tty); - if (tty->fasync && test_and_clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) kill_fasync(&tty->fasync, SIGIO, POLL_OUT); } -- 2.30.2