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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 4C226C43603 for ; Wed, 18 Dec 2019 08:08:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B69C21D7D for ; Wed, 18 Dec 2019 08:08:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Uu9okZqb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726705AbfLRIIh (ORCPT ); Wed, 18 Dec 2019 03:08:37 -0500 Received: from mail-pj1-f67.google.com ([209.85.216.67]:36901 "EHLO mail-pj1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725797AbfLRIIg (ORCPT ); Wed, 18 Dec 2019 03:08:36 -0500 Received: by mail-pj1-f67.google.com with SMTP id m13so514075pjb.2 for ; Wed, 18 Dec 2019 00:08:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=AtCdbC9tz17+3Iqi46yQPht3TnYEo3eyAfKZRFa8DSw=; b=Uu9okZqb35R1qqZLyQd/TYzmHo11HPUoOtCXArpqyI27qg5lsStSN5EoTw/bLj9hc+ aRVBqbR64FtoqPkYlFP9/U6w3qFfDpnlArNyFzijpy7+KLN8fLpWvvEyW3ay61H43cCQ mzCwYC7orfMubgq7XyMDeZy5E6zcFxDPJMEI1lITSPxqbjvzalFUGZ/sgOiK0pu5V75J bhjqv0njVq6X16d9GTahB+LRc8GnWmGa78ZNASHwW3JdPCEng+3SdVk71rsfcKCXh35k nFP7LO1tbHbePAxGCzppwSey9bMVwQh9ea+H3hgoSck8idZZ3HqjLYm9bQu1n+VwBwlv WOEg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=AtCdbC9tz17+3Iqi46yQPht3TnYEo3eyAfKZRFa8DSw=; b=ASPokNfHWBIRrqhTdWki7UQAD/mLmS1CGg6VqdJqbT9h42d0xnDPbAagbQJuLjJizd adcT13eiwHRfzSUOwVBgkYIufn8qGvGNl3aj5/0Dt/o5Eut5hjQrFOVfNkvY60Hdhpts 44NBk2eIsCU4e9vur5dN0sOd+q7M6r/BYXUOFCe6jdWiP2+iOvhTOClGZp4LFPpxAF/f q1wWBqz6YmTky3lEoEaWQRDPjvRRCs0EpLKXWDiq09Tmn7Dh9/j3MQ8pD8bKUrpubxl+ dQlONmZQj63Fm9lU+T7qBlWr5ZoGUOwq4+2PPg6sP7iksOtfUl2EqCZhTSXrp7l/YbWx nnvA== X-Gm-Message-State: APjAAAV9hDjmbwQqFragGrFZUG+W8itHIjJdNjTX1QLMX3RUh1K3Vdsu mzmHSSigpo421m9fIji8NP8= X-Google-Smtp-Source: APXvYqwbhmCf/rOFPQ881Ib2+3RCKMKAYN/te5ELG8JvndET+33eWOAuHzeLltWSrBwtSUoGQ2S9/A== X-Received: by 2002:a17:902:b496:: with SMTP id y22mr1380247plr.158.1576656515550; Wed, 18 Dec 2019 00:08:35 -0800 (PST) Received: from localhost ([43.224.245.179]) by smtp.gmail.com with ESMTPSA id q6sm1943218pfq.27.2019.12.18.00.08.34 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Wed, 18 Dec 2019 00:08:35 -0800 (PST) Date: Wed, 18 Dec 2019 16:08:32 +0800 From: chenqiwu To: Oleg Nesterov Cc: christian.brauner@ubuntu.com, peterz@infradead.org, mingo@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] kernel/exit: do panic earlier to get coredump if global init task exit Message-ID: <20191218080832.GA8408@cqw-OptiPlex-7050> References: <1576466324-6067-1-git-send-email-qiwuchen55@gmail.com> <20191216172841.GA10466@redhat.com> <20191216174410.xiqurqnqyipbuy4e@wittgenstein> <20191217105042.GA21784@cqw-OptiPlex-7050> <20191217142515.GB23152@redhat.com> <20191217145620.GA26585@cqw-OptiPlex-7050> <20191217152333.GC23152@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191217152333.GC23152@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 17, 2019 at 04:23:33PM +0100, Oleg Nesterov wrote: > On 12/17, chenqiwu wrote: > > > > But in fact, I think atomic_read() > > can avoid the racy even if both threads exit in parallel, since it is > > an atomic operation forever. > > Hmm, not sure I understand. atomic_read() is just READ_ONCE(), it can't be > re-ordered but that is all. > > How can it avoid the race if it is called before atomic_dec_and_test() ? > > Again, suppose that we have 2 exiting threads and signal->live == 2. With > your patch each thread does atomic_read() before atomic_dec_and_test(), > both threads can observe atomic_read(signal->live) == 2 simply because > the counter was not decremented yet. > > Oleg. > Yeah, I agree your idea. Now, if there are no further questions, I will resend this as a proper patch for v3.