From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754644AbbIBOlr (ORCPT ); Wed, 2 Sep 2015 10:41:47 -0400 Received: from mail-wi0-f180.google.com ([209.85.212.180]:36826 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752942AbbIBOlq (ORCPT ); Wed, 2 Sep 2015 10:41:46 -0400 MIME-Version: 1.0 In-Reply-To: <55E70518.6010005@hurleysoftware.com> References: <1441138270-17505-1-git-send-email-dvyukov@google.com> <55E70518.6010005@hurleysoftware.com> From: Dmitry Vyukov Date: Wed, 2 Sep 2015 16:41:25 +0200 Message-ID: Subject: Re: [PATCH] tty: fix data race in flush_to_ldisc To: Peter Hurley Cc: Greg Kroah-Hartman , jslaby@suse.com, LKML , Jiri Slaby , Andrey Konovalov , Kostya Serebryany , Alexander Potapenko Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 2, 2015 at 4:18 PM, Peter Hurley wrote: > 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. It sets tty->link->port->itty to NULL _after_ waiting for flush_to_ldisc work to finish. At least this is the intention. Can you explain why it does not do anything? Thank you.