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 1722EC3A589 for ; Tue, 20 Aug 2019 10:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6DB220C01 for ; Tue, 20 Aug 2019 10:16:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="DP3SIkcq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729639AbfHTKQz (ORCPT ); Tue, 20 Aug 2019 06:16:55 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:45453 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728545AbfHTKQy (ORCPT ); Tue, 20 Aug 2019 06:16:54 -0400 Received: by mail-pg1-f194.google.com with SMTP id o13so2957328pgp.12 for ; Tue, 20 Aug 2019 03:16:54 -0700 (PDT) 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=iKtnRnRXyBjoovTvJIaq2YQ2tJPH/EOQqzClVloanFg=; b=DP3SIkcqOUk5qRV022QgDnIYhMRLclsJbQ+iMuhdQeFA6Vy8y4pu0GdWeJS1iSphsx CeoRwgvdNmy74M1YMktAnP+rDB5p8+z0DyOXL+7bgRlbaa0a2dDeCksAHwX41p3+tZz9 27L/xSef5k2wR9z7Wx8BP60dtIyYTV6klemVidrjmXK0naEftG6wNr6TmbjhkjmHzx9J /lRhkqxKpuGN0YLZkExZB0TH/hCMF06Z0cPlO+huQc54Riipp5frvylqrLy4I1ICvyaY d6Dy+3Jc4lBSSUVSu+Rk9pWIwtcxzybEywnLMU7/lEVscGrc8tPufM1b7JT9yR4SeG/Y IMkQ== 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=iKtnRnRXyBjoovTvJIaq2YQ2tJPH/EOQqzClVloanFg=; b=tQyYkAAxxGEWH3JZufqjIj80gSkk7lLGf9cucwaCNxFVXR+iETPmyZHGVv53RfRkGL YwIKILgepsN+KvNFjBKRPGuzclj6V5sdLIqNO+Cgmz6qO3WT86emHwWRtkSQKY6U6l6d gjOeIccerFJBOcsKCfQ4FUUXnfhk04vODghjx/fG1qqxj4T7CFmvq5JzzR+f1sZt/umC 3lff6JNudKdI6SfUwpigx0rIGPsdXz+E05bGhsAvCZ6TPTYIcwOQcQJlSf/+yImf4gGT PQ1hPX3yDKJnWs3cKgS27i/gwPobUtsZ6p6bTBfUTFo6+MVSISqWx825agO7sJuLqhRF UOfQ== X-Gm-Message-State: APjAAAVkYW1vEFwTKYznGrH4c2EKhUsx5OgYdm37Wd4jfZem4GhrelYp bRa8YOzQavFQNU+375sXseruJj8p X-Google-Smtp-Source: APXvYqwgzcLdn0MCog+xQ170OVRC9VgAYrG0bYTJ3m1jyJ55KFyl9rQ0V/CAuip+wgMOjEC0ZAswxw== X-Received: by 2002:a17:90a:b014:: with SMTP id x20mr6255093pjq.60.1566296214062; Tue, 20 Aug 2019 03:16:54 -0700 (PDT) Received: from localhost ([175.223.16.125]) by smtp.gmail.com with ESMTPSA id k3sm12387515pjo.3.2019.08.20.03.16.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Aug 2019 03:16:53 -0700 (PDT) Date: Tue, 20 Aug 2019 19:16:49 +0900 From: Sergey Senozhatsky To: Petr Mladek Cc: John Ogness , linux-kernel@vger.kernel.org, Andrea Parri , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Brendan Higgins , Peter Zijlstra , Thomas Gleixner , Linus Torvalds , Greg Kroah-Hartman Subject: Re: [RFC PATCH v4 4/9] printk-rb: initialize new descriptors as invalid Message-ID: <20190820101649.GC14137@jagdpanzerIV> References: <20190807222634.1723-1-john.ogness@linutronix.de> <20190807222634.1723-5-john.ogness@linutronix.de> <20190820092337.cudkfdfhsu44vlhh@pathway.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190820092337.cudkfdfhsu44vlhh@pathway.suse.cz> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (08/20/19 11:23), Petr Mladek wrote: > > is no risk of the descriptor unexpectedly being determined as > > valid due to dataring head overflowing/wrapping. > > Please, provide more details about the solved race. Is it because > some reader could have reference to an invalid (reused) descriptor? > Can be these invalid descriptors be member of the list? As far as I understand, such descriptors can be on the list: prb_reserve() assign_desc() // pick a new never used descr i = atomic_fetch_inc(&rb->desc_next_unused); d = &rb->descs[i] dataring_desc_init(&d->desc); return d buf = dataring_push() // the oldest data is reserved, but not commited ret = get_new_lpos() if (ret) dataring_desc_init() return NULL if (!buf) numlist_push() _datablock_valid() has a "desc->begin_lpos == desc->next_lpos" check. -ss