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 44AEEC43331 for ; Mon, 11 Nov 2019 20:47:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1872A20659 for ; Mon, 11 Nov 2019 20:47:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573505242; bh=3zQMEK7OYr48r4YyOSUY29EhrSqUnXImkEn3hXa4OeY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=xhTOZovWFXD5ejXAMtRYb6N1nNUHPnHuncZUOpjeHKrYW8V2nbOBDXNhKhKjNvshW nHvXHbnrMQjpMdt1zwLfQmnchn+7o+zEic4gKgwgBOcFK1cvoYYpqe9ImFHI0ziVrp z+SlF8PLA5J7QQjFfuASoqnkBnhpcOIG0MfraB2o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727363AbfKKUrV (ORCPT ); Mon, 11 Nov 2019 15:47:21 -0500 Received: from mail-lj1-f193.google.com ([209.85.208.193]:45305 "EHLO mail-lj1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726877AbfKKUrT (ORCPT ); Mon, 11 Nov 2019 15:47:19 -0500 Received: by mail-lj1-f193.google.com with SMTP id n21so15275955ljg.12 for ; Mon, 11 Nov 2019 12:47:18 -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=OaEDXSnozFKU9AfcCmi3n5mppwBp0l4bFT/aQieMhC0=; b=Zs8Zzq88VsL2T86KxW7IgVWl6ZhIIzNKAf9FuqchaKJtKHaYsoAYP+TPoclakBI6l3 ljes5eRvglTxez5EmHsBrnpio1cu+VIFH8/TCGhqHn3GzE608nn3f94tnbKbNvbVffrZ 6m3v2QDJ6S7Hl1KbBOeyM4E0K5JCKzaUiZKxc= 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=OaEDXSnozFKU9AfcCmi3n5mppwBp0l4bFT/aQieMhC0=; b=he3hLOk+aP+ohJZaoTDT5Bw2sxIobjlbZnz1d7gppdFWta2scjV2+VnOp5x1kwO361 BoYCnAClVL2TriWcLLwaMj8HXcF5YO4O7JFMXtgWGmMONna9SBZAnZ0ZmD3hAY5vBdpE qmhC+TRjM2/+G7Gpx2LaWvoIuO6uZao7Gm6GUEyUdSvVzWX9jQImj9gvSfWwHzvt3guF 1meoypsRSMSY2yu0+xCsAPJhNTcgk5au8p1NKR5boy0xSnc7fR++lP0tS5vzOVuuzjgj /dvNn0H735XRiM5Zx+TG01Rs+4LtYDHapXQ9n098KsRy9i86KGJ6yv6RXEG40JXlCxhQ aaag== X-Gm-Message-State: APjAAAU+mPgY8fADSFVyL3GG1Mu6jDnwOvfzA79cyaZ7lTRpANJCpqmG RDZ0aSK3ymCwvwgTWlMc9AFTb5inmSo= X-Google-Smtp-Source: APXvYqxPMU1H+06lAzEc2assGSH0uW78hGxUMg52WKZD0OkztfxIuVtB7YoVfbkJ47oQvIM4ALtCeQ== X-Received: by 2002:a05:651c:238:: with SMTP id z24mr10301264ljn.36.1573505237219; Mon, 11 Nov 2019 12:47:17 -0800 (PST) Received: from mail-lj1-f169.google.com (mail-lj1-f169.google.com. [209.85.208.169]) by smtp.gmail.com with ESMTPSA id 15sm7088090ljq.62.2019.11.11.12.47.14 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 12:47:14 -0800 (PST) Received: by mail-lj1-f169.google.com with SMTP id d5so5782305ljl.4 for ; Mon, 11 Nov 2019 12:47:14 -0800 (PST) X-Received: by 2002:a2e:982:: with SMTP id 124mr9131365ljj.48.1573505233789; Mon, 11 Nov 2019 12:47:13 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Mon, 11 Nov 2019 12:46:56 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file To: Eric Dumazet Cc: Alan Stern , Marco Elver , Eric Dumazet , syzbot , linux-fsdevel , Linux Kernel Mailing List , syzkaller-bugs , Al Viro , Andrea Parri , "Paul E. McKenney" , LKMM Maintainers -- Akira Yokosawa 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, Nov 11, 2019 at 12:43 PM Linus Torvalds wrote: > > Yeah, maybe we could have some model for marking "this is statistics, > doesn't need to be exact". Side note: that marking MUST NOT be "READ_ONCE + WRITE_ONCE", because that makes gcc create horrible code, and only makes the race worse. At least with a regular add, it might stay as a single r-m-w instruction on architectures that have that, and makes the quality of the statistics slightly better (no preemption etc). So that's an excellent example of where changing code to use WRITE_ONCE actually makes the code objectively worse in practice - even if it might be the same in theory. Linus