Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496AbdCTJW1 (ORCPT ); Mon, 20 Mar 2017 05:22:27 -0400 Received: from mail-vk0-f41.google.com ([209.85.213.41]:35259 "EHLO mail-vk0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752966AbdCTJWJ (ORCPT ); Mon, 20 Mar 2017 05:22:09 -0400 MIME-Version: 1.0 In-Reply-To: <20170320132839.72fac965@canb.auug.org.au> References: <20170320132839.72fac965@canb.auug.org.au> From: Dmitry Vyukov Date: Mon, 20 Mar 2017 10:21:47 +0100 Message-ID: Subject: Re: linux-next: manual merge of the tty tree with the tty.current tree To: Stephen Rothwell Cc: Greg KH , linux-next@vger.kernel.org, LKML , Peter Hurley , Michael Neuling Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2812 Lines: 90 On Mon, Mar 20, 2017 at 3:28 AM, Stephen Rothwell wrote: > Hi Greg, > > Today's linux-next merge of the tty tree got a conflict in: > > drivers/tty/tty_ldisc.c > > between commit: > > 5362544bebe8 ("tty: don't panic on OOM in tty_set_ldisc()") > > from the tty.current tree and commit: > > 71472fa9c52b ("tty: Fix ldisc crash on reopened tty") > > from the tty tree. > > I fixed it up (see below) and can carry the fix as necessary. This > is now fixed as far as linux-next is concerned, but any non trivial > conflicts should be mentioned to your upstream maintainer when your tree > is submitted for merging. You may also want to consider cooperating > with the maintainer of the conflicting tree to minimise any particularly > complex conflicts. > > -- > Cheers, > Stephen Rothwell > > diff --cc drivers/tty/tty_ldisc.c > index b0500a0a87b8,4ee7742dced3..000000000000 > --- a/drivers/tty/tty_ldisc.c > +++ b/drivers/tty/tty_ldisc.c > @@@ -621,14 -669,17 +621,15 @@@ int tty_ldisc_reinit(struct tty_struct > tty_ldisc_put(tty->ldisc); > } > > - /* switch the line discipline */ > - tty->ldisc = ld; > tty_set_termios_ldisc(tty, disc); > - retval = tty_ldisc_open(tty, tty->ldisc); > + retval = tty_ldisc_open(tty, ld); > if (retval) { > - tty_ldisc_put(tty->ldisc); > - tty->ldisc = NULL; > - if (!WARN_ON(disc == N_TTY)) { > - tty_ldisc_put(ld); > - ld = NULL; > - } > ++ tty_ldisc_put(ld); > ++ ld = NULL; > } > + > + /* switch the line discipline */ > + smp_store_release(&tty->ldisc, ld); > return retval; > } > Peter, Looking at your patch "tty: Fix ldisc crash on reopened tty", I think there is a missed barrier in tty_ldisc_ref. A single barrier does not have any effect, they always need to be in pairs. So I think we also need at least: @@ -295,7 +295,8 @@ struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) struct tty_ldisc *ld = NULL; if (ldsem_down_read_trylock(&tty->ldisc_sem)) { - ld = tty->ldisc; + ld = READ_ONCE(tty->ldisc); + read_barrier_depends(); if (!ld) ldsem_up_read(&tty->ldisc_sem); } Or simply: @@ -295,7 +295,8 @@ struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) struct tty_ldisc *ld = NULL; if (ldsem_down_read_trylock(&tty->ldisc_sem)) { - ld = tty->ldisc; + /* pairs with smp_store_release in tty_ldisc_reinit */ + ld = smp_load_acquire(&tty->ldisc); if (!ld) ldsem_up_read(&tty->ldisc_sem); }