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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,LOTS_OF_MONEY,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 A8872C43382 for ; Thu, 27 Sep 2018 14:27:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 294342152A for ; Thu, 27 Sep 2018 14:27:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=thunk.org header.i=@thunk.org header.b="sW1h+Dc3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 294342152A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mit.edu 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 S1728045AbeI0UqX (ORCPT ); Thu, 27 Sep 2018 16:46:23 -0400 Received: from imap.thunk.org ([74.207.234.97]:55496 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727751AbeI0UqX (ORCPT ); Thu, 27 Sep 2018 16:46:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=thunk.org; s=ef5046eb; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=ZYlrqMOhksGog2bsb0hkNk6SNq9XjE4g7z8zHlLl9ZY=; b=sW1h+Dc3eEkvqanxTbpIo5Uc4X AkUyVii2i6yN9XJTAsqVUoMHg79W2GlkdCKaz22uFNxl8ubgna5UI9D1rVT38/cKMykbbQXumlVEp rOt4mn0BvjOsnRYYQ0qPIaxpy/iK1eQhfTzZdd2y3+sHRLIVhcbQYIveksiLx983gHnM=; Received: from root (helo=callcc.thunk.org) by imap.thunk.org with local-esmtp (Exim 4.89) (envelope-from ) id 1g5XGW-00005h-CO; Thu, 27 Sep 2018 14:27:40 +0000 Received: by callcc.thunk.org (Postfix, from userid 15806) id 3E7D97A518E; Thu, 27 Sep 2018 10:27:38 -0400 (EDT) Date: Thu, 27 Sep 2018 10:27:38 -0400 From: "Theodore Y. Ts'o" To: Jeff Layton Cc: Alan Cox , =?utf-8?B?54Sm5pmT5Yas?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Rogier Wolff , Matthew Wilcox Subject: Re: POSIX violation by writeback error Message-ID: <20180927142738.GA27040@thunk.org> Mail-Followup-To: "Theodore Y. Ts'o" , Jeff Layton , Alan Cox , =?utf-8?B?54Sm5pmT5Yas?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Rogier Wolff , Matthew Wilcox References: <486f6105fd4076c1af67dae7fdfe6826019f7ff4.camel@redhat.com> <20180925003044.239531c7@alans-desktop> <0662a4c5d2e164d651a6a116d06da380f317100f.camel@redhat.com> <20180925154627.GC2933@thunk.org> <23cd68a665d27216415dc79367ffc3bee1b60b86.camel@redhat.com> <20180925223054.GH2933@thunk.org> <51b401b82356c2d8e124bb8701f310afd98e0838.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51b401b82356c2d8e124bb8701f310afd98e0838.camel@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 27, 2018 at 08:43:10AM -0400, Jeff Layton wrote: > > Basically, the problem (as I see it) is that we can end up evicting > uncleanable data from the cache before you have a chance to call fsync, > and that means that the results of a read after a write are not > completely reliable. Part of the problem is that people don't agree on what the problem is. :-) The original posting was from someone who claimed it was a "POSIX violation" if a subsequent read returns *successfully*, but then the writeback succeeds. Other people are worried about this problem; yet others are worried about the system wedging and OOM-killing itself, etc. The problem is that in the face of I/O errors, it's impossible to keep everyone happy. (You could make the local storage device completely reliable, with a multi-million dollar storage array with remote replication, but then the CFO won't be happy; and other people were talking about making things work with cheap USB thumb drives and laptops. This is the very definition of an over-constained problem.) - Ted