Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965812Ab2EOCS6 (ORCPT ); Mon, 14 May 2012 22:18:58 -0400 Received: from mail1.windriver.com ([147.11.146.13]:53304 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965011Ab2EOCRF (ORCPT ); Mon, 14 May 2012 22:17:05 -0400 From: Paul Gortmaker To: , Subject: [34-longterm 080/179] TTY: ldisc, do not close until there are readers Date: Mon, 14 May 2012 22:12:56 -0400 Message-ID: <1337048075-6132-81-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.9.6 In-Reply-To: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> References: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4355 Lines: 112 From: Jiri Slaby ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit 92f6fa09bd453ffe3351fa1f1377a1b7cfa911e6 upstream. We restored tty_ldisc_wait_idle in 100eeae2c5c (TTY: restore tty_ldisc_wait_idle). We used it in the ldisc changing path to fix the case where there are tasks in n_tty_read waiting for data and somebody tries to change ldisc. Similar to the case above, there may be also tasks waiting in n_tty_read while hangup is performed. As 65b770468e98 (tty-ldisc: turn ldisc user count into a proper refcount) removed the wait-until-idle from all paths, hangup path won't wait for them to disappear either now. So add it back even to the hangup path. There is a difference, we need uninterruptible sleep as there is obviously HUP signal pending. So tty_ldisc_wait_idle now sleeps without possibility to be interrupted. This is what original tty_ldisc_wait_idle did. After the wait idle reintroduction (100eeae2c5c), we have had interruptible sleeps for the ldisc changing path. But as there is a 5s timeout anyway, we don't allow it to be interrupted from now on. It's not worth the added complexity of deciding what kind of sleep we want. Before 65b770468e98 tty_ldisc_release was called also from tty_ldisc_release. It is called from tty_release, so I don't think we need to restore that one. This is nicely reproducible after constifying the timing when drivers/tty/n_tty.c is patched as follows ("TTY: ntty, add one more sanity check" patch is needed to actually see it explode): %% -1548,6 +1549,7 @@ static int n_tty_open(struct tty_struct *tty) /* These are ugly. Currently a malloc failure here can panic */ if (!tty->read_buf) { + msleep(100); tty->read_buf = kzalloc(N_TTY_BUF_SIZE, GFP_KERNEL); if (!tty->read_buf) return -ENOMEM; %% -1785,6 +1788,7 @@ do_it_again: break; } timeout = schedule_timeout(timeout); + msleep(20); continue; } __set_current_state(TASK_RUNNING); ===== With a process: ===== while (1) { int fd = open(argv[1], O_RDWR); read(fd, buf, sizeof(buf)); close(fd); } ===== and its child: ===== setsid(); while (1) { int fd = open(tty, O_RDWR|O_NOCTTY); ioctl(fd, TIOCSCTTY, 1); vhangup(); close(fd); usleep(100 * (10 + random() % 1000)); } ===== EOF ===== References: https://bugzilla.novell.com/show_bug.cgi?id=693374 References: https://bugzilla.novell.com/show_bug.cgi?id=694509 Signed-off-by: Jiri Slaby Cc: Alan Cox Cc: Linus Torvalds Signed-off-by: Greg Kroah-Hartman [PG: account for char --> tty file rename post 2.6.34] Signed-off-by: Paul Gortmaker --- drivers/char/tty_ldisc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c index 236628f..48de74a 100644 --- a/drivers/char/tty_ldisc.c +++ b/drivers/char/tty_ldisc.c @@ -543,7 +543,7 @@ static int tty_ldisc_halt(struct tty_struct *tty) static int tty_ldisc_wait_idle(struct tty_struct *tty) { int ret; - ret = wait_event_interruptible_timeout(tty_ldisc_idle, + ret = wait_event_timeout(tty_ldisc_idle, atomic_read(&tty->ldisc->users) == 1, 5 * HZ); if (ret < 0) return ret; @@ -750,6 +750,8 @@ static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc) if (IS_ERR(ld)) return -1; + WARN_ON_ONCE(tty_ldisc_wait_idle(tty)); + tty_ldisc_close(tty, tty->ldisc); tty_ldisc_put(tty->ldisc); tty->ldisc = NULL; -- 1.7.9.6 -- 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/