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=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, T_DKIMWL_WL_HIGH,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=unavailable 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 D3354C28CC0 for ; Wed, 29 May 2019 23:11:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC31D2430A for ; Wed, 29 May 2019 23:11:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559171477; bh=A7U+MKtbpL0dbOSwe7NVUwPsEv1DCY3eyaHKJ9yij5Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=vDN7J12Mlec1rGtTs4X22x1bW8MfTSyc7AmQitexqudQdz5mfsXogKl+YeBOm1yTT YsvXcXyBvJC/I7W46WEoweRiGYP7LZw7t5fx1NsXveoI1k1ULoBcMqTcXlyKCyuu6/ SiYGKgZa7vfHZ4depmQXtiLLMhKtxSh1GhrrW00g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726837AbfE2XLN (ORCPT ); Wed, 29 May 2019 19:11:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:35252 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726454AbfE2XLN (ORCPT ); Wed, 29 May 2019 19:11:13 -0400 Received: from localhost (unknown [207.225.69.115]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A46C024305; Wed, 29 May 2019 23:11:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559171472; bh=A7U+MKtbpL0dbOSwe7NVUwPsEv1DCY3eyaHKJ9yij5Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DnSJfxskqxpoQDrJRLWPU3NKJ9nfYdmkllbJE1jasU/tSrYzbQeEsRa/tEIwqDZA1 58t5pmRoasRn8uJ1R9YBMOP9PLM6McjNKfMxSrTAqzTZ1uhDbKtwQqlK+rfABj+Un2 qEmgNaK4na4weQeZUl4U347gLc9xz8YWC4qIuY8E= Date: Wed, 29 May 2019 16:11:12 -0700 From: Greg KH To: David Howells Cc: viro@zeniv.linux.org.uk, raven@themaw.net, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-block@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer Message-ID: <20190529231112.GB3164@kroah.com> References: <20190528231218.GA28384@kroah.com> <20190528162603.GA24097@kroah.com> <155905930702.7587.7100265859075976147.stgit@warthog.procyon.org.uk> <155905931502.7587.11705449537368497489.stgit@warthog.procyon.org.uk> <4031.1559064620@warthog.procyon.org.uk> <31936.1559146000@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <31936.1559146000@warthog.procyon.org.uk> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Wed, May 29, 2019 at 05:06:40PM +0100, David Howells wrote: > Greg KH wrote: > > And how does the tracing and perf ring buffers do this without needing > > volatile? Why not use the same type of interface they provide, as it's > > always good to share code that has already had all of the nasty corner > > cases worked out. > > I've no idea how trace does it - or even where - or even if. As far as I can > see, grepping for mmap in kernel/trace/*, there's no mmap support. > > Reading Documentation/trace/ring-buffer-design.txt the trace subsystem has > some sort of transient page fifo which is a lot more complicated than what I > want and doesn't look like it'll be mmap'able. > > Looking at the perf ring buffer, there appears to be a missing barrier in > perf_aux_output_end(): > > rb->user_page->aux_head = rb->aux_head; > > should be: > > smp_store_release(&rb->user_page->aux_head, rb->aux_head); > > It should also be using smp_load_acquire(). See > Documentation/core-api/circular-buffers.rst > > And a (partial) patch has been proposed: https://lkml.org/lkml/2018/5/10/249 So, if that's all that needs to be fixed, can you use the same buffer/code if that patch is merged? thanks, greg k-h