From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02C6EC04ABB for ; Tue, 11 Sep 2018 12:53:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A44820833 for ; Tue, 11 Sep 2018 12:53:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="ghEsHE6o" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7A44820833 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=arista.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727535AbeIKRxA (ORCPT ); Tue, 11 Sep 2018 13:53:00 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:46545 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726761AbeIKRxA (ORCPT ); Tue, 11 Sep 2018 13:53:00 -0400 Received: by mail-ed1-f65.google.com with SMTP id k14-v6so19125884edr.13 for ; Tue, 11 Sep 2018 05:53:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=message-id:subject:from:to:cc:date:in-reply-to:references :mime-version:content-transfer-encoding; bh=+JH9R72BpdbC+YFzP6QfB2OWaJNzQfdimLRrJZhUgl0=; b=ghEsHE6oAVGUoeCrs6NcT3YFoFECdNhyv3qN53HNmZrSklq4cAO9Yo23rcaiKaZSgZ HpgJbEfkJ6nWX9gLOw8l567kEoUq3/JWl2WQXVBsYn+ub3EYinX8JsG6sPznzfXCG13g CuGJ6sh99KKoLEWd9v2viyaImc5dIGIM6j3b6LPe69f3CDR0BGWdpG3DX58rxnqc4wU7 CYntKBLYJPY3bVXdCyciDhVLd8JaXz852CursQxxI5u/q3TsrhaMzE6DYV/lbKj84udx 6GAN6qWy5PAmewEb1LVg3jIRskgcbqqMV0VGey4rZhwlmQVKP0a4qwMbX+JtkzMuqGRd keFA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=+JH9R72BpdbC+YFzP6QfB2OWaJNzQfdimLRrJZhUgl0=; b=gyn4VX0Z94YwxnU91J6liGhR4rbh43MXhsV1K4uUSRksiMP/gJdW83xgy0h4amDK/B ShIIbt7mnAPmDy+fnK9L7FuBvUt5ZSbIxcySUA3qEVO5pbdweiJdCCYw4FP3Te6u4S8W VHvej4NgHs3SGpcCK1btEj84QZwT3q9m5U8eLDRwaAoqtzu03KDqq4eFWhN5bI+N1naV M5mbFYzZbPWRs/II36mltLCPNRr5vUoBSYLfwEO6hkAuUkcrI9wJv98w9+6apPL6dVNC ni1/ia7FtMayR1dmdJfSQUGX7d9d41ZnyRibyTam7b97DK9YC5EPrdNiw3qIDcsg0CuM phwA== X-Gm-Message-State: APzg51Btg2I77cyfsOpEw7eyVFYahauUi08iEG3SCiOV05zZyvrEuhn9 /p8ndqas6xFeG7mkWcbs5R6rVg== X-Google-Smtp-Source: ANB0VdaPbWjeNvdtyQ8qVbA+N+PSvnPeXoQODG4s54aRXySuOQxkGPcVAoK4vcjNK6FC0vQgTQbFIw== X-Received: by 2002:a50:8b65:: with SMTP id l92-v6mr28516377edl.44.1536670426784; Tue, 11 Sep 2018 05:53:46 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id x32-v6sm13445908eda.81.2018.09.11.05.53.45 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 11 Sep 2018 05:53:46 -0700 (PDT) Message-ID: <1536670424.2710.22.camel@arista.com> Subject: Re: [PATCHv3 4/6] tty/lockdep: Add ldisc_sem asserts From: Dmitry Safonov To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Dmitry Safonov <0x7f454c46@gmail.com>, Daniel Axtens , Dmitry Vyukov , Michael Neuling , Mikulas Patocka , Nathan March , Pasi =?ISO-8859-1?Q?K=E4rkk=E4inen?= , Peter Hurley , "Rong, Chen" , Sergey Senozhatsky , Tan Xiaojun , Tetsuo Handa , Greg Kroah-Hartman , Jiri Slaby Date: Tue, 11 Sep 2018 13:53:44 +0100 In-Reply-To: <20180911120153.GB19234@hirez.programming.kicks-ass.net> References: <20180911014821.26286-1-dima@arista.com> <20180911014821.26286-5-dima@arista.com> <20180911120153.GB19234@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.24.6 (3.24.6-1.fc26) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2018-09-11 at 14:01 +0200, Peter Zijlstra wrote: > On Tue, Sep 11, 2018 at 02:48:19AM +0100, Dmitry Safonov wrote: > > Make sure under CONFIG_LOCKDEP that each change to line discipline > > is done with held write semaphor. > > But you don't do that. You just assert it is held, not for writing. > > > Otherwise potential reader will have a good time dereferencing > > incomplete/uninitialized ldisc. > > > > Exception here is tty_ldisc_open(), as it's called without > > ldisc_sem > > locked by tty_init_dev() for the tty->link. > > You fail to explain how that is not broken... I'll add the explanation to the next version. > > > Cc: Greg Kroah-Hartman > > Cc: Jiri Slaby > > Signed-off-by: Dmitry Safonov > > --- > > drivers/tty/tty_ldisc.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c > > index fc4c97cae01e..202cb645582f 100644 > > --- a/drivers/tty/tty_ldisc.c > > +++ b/drivers/tty/tty_ldisc.c > > @@ -471,6 +471,7 @@ static int tty_ldisc_open(struct tty_struct > > *tty, struct tty_ldisc *ld) > > > > static void tty_ldisc_close(struct tty_struct *tty, struct > > tty_ldisc *ld) > > { > > + lockdep_assert_held(&tty->ldisc_sem); > > Did you want: > > lockdep_assert_held_exclusive(&tty->ldisc_sem); > > ? Oh, yes, thanks. > > > WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags)); > > clear_bit(TTY_LDISC_OPEN, &tty->flags); > > if (ld->ops->close) -- Thanks, Dmitry