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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 AAAD5C43603 for ; Mon, 9 Dec 2019 18:03:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A904207FF for ; Mon, 9 Dec 2019 18:03:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575914614; bh=Ho6NIaCNXfbkLEOMsuOLOK6gq9sAAuapYyd79Asasxk=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=uyt3NSX9arzs+5cm1kq7hW6J1cwheL1MP2eryf52WX37ZcOJIUOIIRPtt31bNZdad 2cjVV+IPOODvfj++w59Hg14R8JnV6Aq5EjAwEDpcGp3nVAbx8Jvv10V0HR/DWaufJF GvzLe8Fvczs7MsV/0rSQwltf+VocobC+JfMPpfok= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726874AbfLISDd (ORCPT ); Mon, 9 Dec 2019 13:03:33 -0500 Received: from mail-lf1-f53.google.com ([209.85.167.53]:36911 "EHLO mail-lf1-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726379AbfLISDd (ORCPT ); Mon, 9 Dec 2019 13:03:33 -0500 Received: by mail-lf1-f53.google.com with SMTP id b15so11447717lfc.4 for ; Mon, 09 Dec 2019 10:03:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=PpeayAw5RjosR9XsravUrBYg0E2pZAf0Pj7kxkBeMwQ=; b=LUAUPaeNDU6XQY5PvOsRTTNlTiJvWnF1rDQwxJZEDyC2iEwn8AaHrWqBf/A9/cXCba +4+rN3MzgxVmbvRFRnNdliSz/J/bsVEJ12fRPqK3GbO24nDJT5GLlRmFTEFrhhXpWvh4 mWoerzE83OXDTE0wQspdalsWrEsrvNRBkYfbs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PpeayAw5RjosR9XsravUrBYg0E2pZAf0Pj7kxkBeMwQ=; b=rt/4kzddH7cIGpiGN/SMNDA5eBhXkGFT+IBva8egy2say/+HLAZR9OjxdazBknDnd4 GshEF5MA5065NKj4xwPft8s4WpNkavAZjmORO5INQU2AJx4kw4RpP5Ur59gMAVOFvmi4 oYpGhj5CbJSTaXtSX3Yfi+gkr3myrNaqc2Qdxk9KjkDWQOj83Wl0v9Kmmcd1fUEvW5c9 ohFwHUnllqYRtUGL1z9ly9jd1A9SvxCgZMdp19isxkmaZTOivgoHVDcOmRqyA4m9qmHT EZQip8YXtMnlt739dpangcIKCxPETrc07MY897IOFILktephkA/SozO74i6osugDXdqh ymwg== X-Gm-Message-State: APjAAAWkTBPuN2K8EhvJTguxOzJMkuRhz92BDA2m4SkieCTaKtxKw0bt t5MSPkmrTrkAluVIw34tWXnEEt//JOI= X-Google-Smtp-Source: APXvYqxVylMz11aR/tS23/e/Aui83Lr6hzEBl0nClHPBdCFQJwi8QiuFuDznckAMs2Xf5RV9u1rrJA== X-Received: by 2002:ac2:5a09:: with SMTP id q9mr6700194lfn.71.1575914608921; Mon, 09 Dec 2019 10:03:28 -0800 (PST) Received: from mail-lf1-f48.google.com (mail-lf1-f48.google.com. [209.85.167.48]) by smtp.gmail.com with ESMTPSA id e8sm359696ljb.45.2019.12.09.10.03.27 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Dec 2019 10:03:27 -0800 (PST) Received: by mail-lf1-f48.google.com with SMTP id m30so11431866lfp.8 for ; Mon, 09 Dec 2019 10:03:27 -0800 (PST) X-Received: by 2002:ac2:555c:: with SMTP id l28mr15967030lfk.52.1575914607385; Mon, 09 Dec 2019 10:03:27 -0800 (PST) MIME-Version: 1.0 References: <20191209173820.GA11415@redhat.com> In-Reply-To: <20191209173820.GA11415@redhat.com> From: Linus Torvalds Date: Mon, 9 Dec 2019 10:03:11 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Fundamental race condition in wait_event_interruptible_exclusive() ? To: Oleg Nesterov Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Miklos Szeredi , Linux Kernel Mailing List , Felipe Balbi Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 9, 2019 at 9:38 AM Oleg Nesterov wrote: > > > because we've added ourselves as an exclusive writer to the > > queue. So it _says_ it was interrupted, not woken up, and the wait got > > cancelled, but because we were an exclusive waiter, we might be the > > _only_ thing that got woken up, > > And that is why ___wait_event() always checks the condition after > prepare_to_wait_event(), whatever it returns. Ack. I misread the code, and you're right - if we've been woken up, the condition is supposed to be true, and we never actually return -ERESTARTSYS. So the situation of "got woken but returned error, and lost wakeup" won't actually ever happen. Good. So yeah, I can do what I wanted to do, and it should all work. I never even tested it, because I was getting fairly anal about possible races in the pipe code by then. Linus