Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752802AbaJPTe6 (ORCPT ); Thu, 16 Oct 2014 15:34:58 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:51580 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751472AbaJPTdz (ORCPT ); Thu, 16 Oct 2014 15:33:55 -0400 From: Peter Hurley To: Greg Kroah-Hartman Cc: Jiri Slaby , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, One Thousand Gnomes , Peter Hurley Subject: [PATCH -next 8/9] tty: Fix missed wakeup from packet mode status update Date: Thu, 16 Oct 2014 15:33:29 -0400 Message-Id: <1413488010-16885-9-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 2.1.1 In-Reply-To: <1413488010-16885-1-git-send-email-peter@hurleysoftware.com> References: <1413488010-16885-1-git-send-email-peter@hurleysoftware.com> 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 The pty master read() can miss the wake up for a packet mode status change. For example, CPU 0 | CPU 1 n_tty_read() | n_tty_packet_mode_flush() ... | . if (packet & link->ctrl_status) { | . /* no new ctrl_status ATM */ | . | spin_lock | ctrl_status |= TIOCPKT_FLUSHREAD | spin_unlock | wake_up(link->read_wait) } | set_current_state(TASK_INTERRUPTIBLE) | ... | The pty master read() will now sleep (assuming there is no input) having missed the read_wait wakeup. Set the task state before the condition test. Signed-off-by: Peter Hurley --- drivers/tty/n_tty.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 6a42204..602dbc2 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2168,6 +2168,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, add_wait_queue(&tty->read_wait, &wait); while (nr) { + /* This statement must be first before checking for input + so that any interrupt will set the state back to + TASK_RUNNING. */ + set_current_state(TASK_INTERRUPTIBLE); + /* First test for status change. */ if (packet && tty->link->ctrl_status) { unsigned char cs; @@ -2185,10 +2190,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, nr--; break; } - /* This statement must be first before checking for input - so that any interrupt will set the state back to - TASK_RUNNING. */ - set_current_state(TASK_INTERRUPTIBLE); if (((minimum - (b - buf)) < ldata->minimum_to_wake) && ((minimum - (b - buf)) >= 1)) -- 2.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/