Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752263AbbLLWQs (ORCPT ); Sat, 12 Dec 2015 17:16:48 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:33190 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751238AbbLLWQo (ORCPT ); Sat, 12 Dec 2015 17:16:44 -0500 From: Peter Hurley To: Greg Kroah-Hartman Cc: Jiri Slaby , linux-kernel@vger.kernel.org, Peter Hurley Subject: [PATCH 1/6] n_tty: Always wake up read()/poll() if new input Date: Sat, 12 Dec 2015 14:16:34 -0800 Message-Id: <1449958599-5533-2-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 2.6.3 In-Reply-To: <1449958599-5533-1-git-send-email-peter@hurleysoftware.com> References: <1449958599-5533-1-git-send-email-peter@hurleysoftware.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4540 Lines: 130 A read() in non-canonical mode when VMIN > 0 and VTIME == 0 does not complete until at least VMIN chars have been read (or the user buffer is full). In this infrequent read mode, n_tty_read() attempts to reduce wakeups by computing the amount of data still necessary to complete the read (minimum_to_wake) and only waking the read()/poll() when that much unread data has been processed. This is the only read mode for which new data does not necessarily generate a wakeup. However, this optimization is broken and commonly leads to hung reads even though the necessary amount of data has been received. Since the optimization is of marginal value anyway, just remove the whole thing. This also remedies a race between a concurrent poll() and read() in this mode, where the poll() can reset the minimum_to_wake of the read() (and vice versa). Signed-off-by: Peter Hurley --- drivers/tty/n_tty.c | 33 ++------------------------------- 1 file changed, 2 insertions(+), 31 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 4e1867a..16ba07b 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -113,7 +113,6 @@ struct n_tty_data { DECLARE_BITMAP(read_flags, N_TTY_BUF_SIZE); unsigned char echo_buf[N_TTY_BUF_SIZE]; - int minimum_to_wake; int closing; /* consumer-published */ @@ -1632,7 +1631,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp, /* publish read_head to consumer */ smp_store_release(&ldata->commit_head, ldata->read_head); - if ((read_cnt(ldata) >= ldata->minimum_to_wake) || L_EXTPROC(tty)) { + if (read_cnt(ldata)) { kill_fasync(&tty->fasync, SIGIO, POLL_IN); wake_up_interruptible_poll(&tty->read_wait, POLLIN); } @@ -1899,7 +1898,6 @@ static int n_tty_open(struct tty_struct *tty) reset_buffer_flags(tty->disc_data); ldata->column = 0; ldata->canon_column = 0; - ldata->minimum_to_wake = 1; ldata->num_overrun = 0; ldata->no_room = 0; ldata->lnext = 0; @@ -2162,14 +2160,9 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, minimum = MIN_CHAR(tty); if (minimum) { time = (HZ / 10) * TIME_CHAR(tty); - if (time) - ldata->minimum_to_wake = 1; - else if (!waitqueue_active(&tty->read_wait) || - (ldata->minimum_to_wake > minimum)) - ldata->minimum_to_wake = minimum; } else { timeout = (HZ / 10) * TIME_CHAR(tty); - ldata->minimum_to_wake = minimum = 1; + minimum = 1; } } @@ -2196,10 +2189,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, break; } - if (((minimum - (b - buf)) < ldata->minimum_to_wake) && - ((minimum - (b - buf)) >= 1)) - ldata->minimum_to_wake = (minimum - (b - buf)); - done = check_other_done(tty); if (!input_available_p(tty, 0)) { @@ -2265,9 +2254,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, up_read(&tty->termios_rwsem); remove_wait_queue(&tty->read_wait, &wait); - if (!waitqueue_active(&tty->read_wait)) - ldata->minimum_to_wake = minimum; - mutex_unlock(&ldata->atomic_read_lock); if (b - buf) @@ -2402,7 +2388,6 @@ break_out: static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file, poll_table *wait) { - struct n_tty_data *ldata = tty->disc_data; unsigned int mask = 0; poll_wait(file, &tty->read_wait, wait); @@ -2415,12 +2400,6 @@ static unsigned int n_tty_poll(struct tty_struct *tty, struct file *file, mask |= POLLPRI | POLLIN | POLLRDNORM; if (tty_hung_up_p(file)) mask |= POLLHUP; - if (!(mask & (POLLHUP | POLLIN | POLLRDNORM))) { - if (MIN_CHAR(tty) && !TIME_CHAR(tty)) - ldata->minimum_to_wake = MIN_CHAR(tty); - else - ldata->minimum_to_wake = 1; - } if (tty->ops->write && !tty_is_writelocked(tty) && tty_chars_in_buffer(tty) < WAKEUP_CHARS && tty_write_room(tty) > 0) @@ -2471,14 +2450,6 @@ static int n_tty_ioctl(struct tty_struct *tty, struct file *file, static void n_tty_fasync(struct tty_struct *tty, int on) { - struct n_tty_data *ldata = tty->disc_data; - - if (!waitqueue_active(&tty->read_wait)) { - if (on) - ldata->minimum_to_wake = 1; - else if (!tty->fasync) - ldata->minimum_to_wake = N_TTY_BUF_SIZE; - } } static void n_tty_closing(struct tty_struct *tty) -- 2.6.3 -- 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/