From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932180AbaHGLOa (ORCPT ); Thu, 7 Aug 2014 07:14:30 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:33130 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932089AbaHGLO2 (ORCPT ); Thu, 7 Aug 2014 07:14:28 -0400 From: Peter Hurley To: Greg Kroah-Hartman Cc: Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Hurley Subject: [PATCH] tty: Fix spurious poll() wakeups Date: Thu, 7 Aug 2014 07:14:10 -0400 Message-Id: <1407410050-32198-1-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 2.0.4 X-Authenticated-User: 990527 peter@hurleysoftware.com X-MT-ID: 8FA290C2A27252AACF65DBC4A42F3CE3735FB2A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the N_TTY line discipline receives data and wakes readers to process the input, polling writers are also mistakenly woken. This is because, although readers and writers are differentiated by different wait queues (tty->read_wait & tty->write_wait), both wait queues are polled together. Thus, reader wakeups without poll flags still cause poll(POLLOUT) to wakeup. For received data, wakeup readers with POLLIN. Preserve the unspecific wakeup in n_tty_packet_mode_flush(), as this action should flag both POLLIN and POLLOUT. Fixes epoll_wait() for edge-triggered EPOLLOUT. Signed-off-by: Peter Hurley --- drivers/tty/n_tty.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index f44f1ba..89c4cee 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1166,7 +1166,7 @@ static void n_tty_receive_break(struct tty_struct *tty) } put_tty_queue('\0', ldata); if (waitqueue_active(&tty->read_wait)) - wake_up_interruptible(&tty->read_wait); + wake_up_interruptible_poll(&tty->read_wait, POLLIN); } /** @@ -1226,7 +1226,7 @@ static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c) } else put_tty_queue(c, ldata); if (waitqueue_active(&tty->read_wait)) - wake_up_interruptible(&tty->read_wait); + wake_up_interruptible_poll(&tty->read_wait, POLLIN); } static void @@ -1378,7 +1378,7 @@ handle_newline: ldata->canon_head = ldata->read_head; kill_fasync(&tty->fasync, SIGIO, POLL_IN); if (waitqueue_active(&tty->read_wait)) - wake_up_interruptible(&tty->read_wait); + wake_up_interruptible_poll(&tty->read_wait, POLLIN); return 0; } } @@ -1679,7 +1679,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp, L_EXTPROC(tty)) { kill_fasync(&tty->fasync, SIGIO, POLL_IN); if (waitqueue_active(&tty->read_wait)) - wake_up_interruptible(&tty->read_wait); + wake_up_interruptible_poll(&tty->read_wait, POLLIN); } } -- 2.0.4