From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754688AbbIBOSH (ORCPT ); Wed, 2 Sep 2015 10:18:07 -0400 Received: from mail-qk0-f170.google.com ([209.85.220.170]:33485 "EHLO mail-qk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753579AbbIBOSD (ORCPT ); Wed, 2 Sep 2015 10:18:03 -0400 Subject: Re: [PATCH] tty: fix data race in flush_to_ldisc To: Dmitry Vyukov , gregkh@linuxfoundation.org References: <1441138270-17505-1-git-send-email-dvyukov@google.com> Cc: jslaby@suse.com, linux-kernel@vger.kernel.org, jslaby@suse.cz, andreyknvl@google.com, kcc@google.com, glider@google.com From: Peter Hurley Message-ID: <55E70518.6010005@hurleysoftware.com> Date: Wed, 2 Sep 2015 10:18:00 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <1441138270-17505-1-git-send-email-dvyukov@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/01/2015 04:11 PM, Dmitry Vyukov wrote: > The data race is found with KernelThreadSanitizer (on rev 21bdb584af8c): > > ThreadSanitizer: data-race in release_tty > Write of size 8 by thread T325 (K2579): > release_tty+0xf3/0x1c0 drivers/tty/tty_io.c:1688 > tty_release+0x698/0x7c0 drivers/tty/tty_io.c:1920 > __fput+0x15f/0x310 fs/file_table.c:207 > ____fput+0x1d/0x30 fs/file_table.c:243 > task_work_run+0x115/0x130 kernel/task_work.c:123 > do_notify_resume+0x73/0x80 > tracehook_notify_resume include/linux/tracehook.h:190 > do_notify_resume+0x73/0x80 arch/x86/kernel/signal.c:757 > int_signal+0x12/0x17 arch/x86/entry/entry_64.S:326 > Previous read of size 8 by thread T19 (K16): > flush_to_ldisc+0x29/0x300 drivers/tty/tty_buffer.c:472 > process_one_work+0x47e/0x930 kernel/workqueue.c:2036 > worker_thread+0xb0/0x900 kernel/workqueue.c:2170 > kthread+0x150/0x170 kernel/kthread.c:207 > > flush_to_ldisc reads port->itty and checks that it is not NULL, > concurrently release_tty sets port->itty to NULL. It is possible > that flush_to_ldisc loads port->itty once, ensures that it is > not NULL, but then reloads it again and uses. The second load > can already return NULL, which will cause a crash. > > Set port->itty to NULL after shutting down flush_to_ldisc work. > > Signed-off-by: Dmitry Vyukov > --- > drivers/tty/tty_io.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index 57fc6ee..0df24c1 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -1684,9 +1684,9 @@ static void release_tty(struct tty_struct *tty, int idx) > tty_free_termios(tty); > tty_driver_remove_tty(tty->driver, tty); > tty->port->itty = NULL; > + cancel_work_sync(&tty->port->buf.work); > if (tty->link) > tty->link->port->itty = NULL; > - cancel_work_sync(&tty->port->buf.work); This patch doesn't do anything. Regards, Peter Hurley > > tty_kref_put(tty->link); > tty_kref_put(tty); >