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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BC6B7C433F5 for ; Tue, 8 Mar 2022 17:40:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348376AbiCHRli (ORCPT ); Tue, 8 Mar 2022 12:41:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55820 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347792AbiCHRlh (ORCPT ); Tue, 8 Mar 2022 12:41:37 -0500 Received: from mail-lf1-x136.google.com (mail-lf1-x136.google.com [IPv6:2a00:1450:4864:20::136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B18D506EA for ; Tue, 8 Mar 2022 09:40:40 -0800 (PST) Received: by mail-lf1-x136.google.com with SMTP id w12so9204475lfr.9 for ; Tue, 08 Mar 2022 09:40:39 -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=j4HcIA5ZURFOUl98GOVrefN75djtXjyZm8o/dMFbKz8=; b=XUxN+P64bilcPljqWgWX3wqVnw3FZMXB5ZH4wIfuAfuPKU8hucKGsVwl/+klugjHvC xd1iG9Sq95/OIhQAcijP56EOmxpcFGCDgrpONQjnZ4xtLxScBr0K/bZ22n0j5UyeCIsH RdkV3T99Y854qU87ErGuLfUzTChN5wVlQfXLw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=j4HcIA5ZURFOUl98GOVrefN75djtXjyZm8o/dMFbKz8=; b=xc0nbFU47q0yGjkAADRgn4MqP8gMuQt7qfBNY3FZ0bSjpOXIkPwJagW8F8gP2JimBE OWPZ7IrzqK0aq95vgrDrFh7wFevI5U97Xylluifuc62rpVB8yzzBQWj9PwFDpvTQ2X3j F5fUZcreg3/IWscoTWmm4JzOW6v21lcLEJwqeTWmAw3Ywinad47YTDXinMXNPFXJKt2p cM3XMwqTHQ3CgsaqbpV9Gt7vja3QQDe73i1XD59i52QTC+BhSE5cg53FZg4E5pmtKW8i vdk9miB+eBe/HaqZ6sf1gFJNXynC2HW2cOB/1bahORVqztvZCnDUlVdUvON6QBRPPx0p qgoQ== X-Gm-Message-State: AOAM530ruQMAEdVgD3hvRcBSDmDamw2WwGoqi5znW5JSx30sDKuz+XpP canOrbD6UqFBxnfiBttmKmufa15/TpTgrdIH4yA= X-Google-Smtp-Source: ABdhPJyWPskkN7Wy6Vjkqtas293Om6RyqyZ6MvAKRCtPDYwJqtBdl87IRYIoj0SnfEDn9jfjD3CfFA== X-Received: by 2002:ac2:5229:0:b0:448:1bd5:35c7 with SMTP id i9-20020ac25229000000b004481bd535c7mr11642808lfl.520.1646761234912; Tue, 08 Mar 2022 09:40:34 -0800 (PST) Received: from mail-lf1-f45.google.com (mail-lf1-f45.google.com. [209.85.167.45]) by smtp.gmail.com with ESMTPSA id l9-20020a2ea309000000b00246299de080sm3976914lje.48.2022.03.08.09.40.32 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Mar 2022 09:40:33 -0800 (PST) Received: by mail-lf1-f45.google.com with SMTP id l20so8919647lfg.12 for ; Tue, 08 Mar 2022 09:40:32 -0800 (PST) X-Received: by 2002:a19:e048:0:b0:448:2caa:7ed2 with SMTP id g8-20020a19e048000000b004482caa7ed2mr8519640lfj.449.1646761232492; Tue, 08 Mar 2022 09:40:32 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Tue, 8 Mar 2022 09:40:16 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Buffered I/O broken on s390x with page faults disabled (gfs2) To: David Hildenbrand Cc: Andreas Gruenbacher , Alexander Viro , linux-s390 , Linux-MM , linux-fsdevel , linux-btrfs Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Mar 8, 2022 at 9:26 AM Linus Torvalds wrote: > > Your actual patch looks pretty nasty, though. We avoid marking it > accessed on purpose (to avoid atomicity issues wrt hw-dirty bits etc), > but still, that patch makes me go "there has to be a better way". That better way might be to make q() not use GUP at all. It doesn't want the page - it just wants to make sure the fault is handled. For the fault_in_readable() case we already just do the user access. The only reason we don't do that for fault_in_safe_writeable() is that we don't have a good non-destructive user write. Hmm. The futex code actually uses "fixup_user_fault()" for this case. Maybe fault_in_safe_writeable() should do that? Linus