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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A4745C28CC2 for ; Wed, 29 May 2019 21:03:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7D2DD241C7 for ; Wed, 29 May 2019 21:03:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726673AbfE2VDF (ORCPT ); Wed, 29 May 2019 17:03:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38918 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726411AbfE2VDE (ORCPT ); Wed, 29 May 2019 17:03:04 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 419FD308213F; Wed, 29 May 2019 21:02:49 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-120-173.rdu2.redhat.com [10.10.120.173]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7EC755DD95; Wed, 29 May 2019 21:02:44 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <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> <20190528231218.GA28384@kroah.com> <31936.1559146000@warthog.procyon.org.uk> To: Jann Horn Cc: dhowells@redhat.com, Greg KH , Al Viro , raven@themaw.net, linux-fsdevel , Linux API , linux-block@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module , kernel list , Kees Cook , Kernel Hardening Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <16192.1559163763.1@warthog.procyon.org.uk> Date: Wed, 29 May 2019 22:02:43 +0100 Message-ID: <16193.1559163763@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 29 May 2019 21:03:04 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Jann Horn wrote: > Does this mean that refcount_read() isn't sufficient for what you want > to do with tracing (because for some reason you actually need to know > the values atomically at the time of increment/decrement)? Correct. There's a gap and if an interrupt or something occurs, it's sufficiently big for the refcount trace to go weird. I've seen it in afs/rxrpc where the incoming network packets that are part of the rxrpc call flow disrupt the refcounts noted in trace lines. David