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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 9D7A9C04AB6 for ; Fri, 31 May 2019 11:15:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 719162681C for ; Fri, 31 May 2019 11:15:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TZRqiz+e" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727053AbfEaLPD (ORCPT ); Fri, 31 May 2019 07:15:03 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:42694 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726240AbfEaLPC (ORCPT ); Fri, 31 May 2019 07:15:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; 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=0bzCcEeHXEwR7c+WQ7EMhHPHTFa6pRbMCfQNYRgGQ50=; b=TZRqiz+eB19FKOviEbwMF50eL tkVinge7hG7nufh2+jXjJimy3MX8tBcxRj3YQ//UpQYvtJgMfKOhWXOXbYLoPoseaA8GM16AkT9se Jngp47DXJ0z8Aw/MuS1HRC8U73Vd1LivUdfY5v/tC0ZNDKoBOdj6+6VODUmz8iT2gJDy2a+4tpMBx VO+5A3Gl8tI5ZU5dfFyOOeE7KYOq4wxlJF67H2SjwQSOphmha3VHx2Fo9JYu9EsuOvlTOySnke9tM z2Nkt7Oukx13QfyTJ/CxJdaCY4q6AKkM/OC82uZli8h02Sua/xANMZ4b54zPgJGxij2HRdkFUR5Ql hCLOaznLw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hWfUl-0002gF-9Z; Fri, 31 May 2019 11:14:47 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BA181201D5AB1; Fri, 31 May 2019 13:14:45 +0200 (CEST) Date: Fri, 31 May 2019 13:14:45 +0200 From: Peter Zijlstra To: David Howells Cc: Jann Horn , 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 Message-ID: <20190531111445.GO2677@hirez.programming.kicks-ass.net> 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> <16193.1559163763@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <16193.1559163763@warthog.procyon.org.uk> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, May 29, 2019 at 10:02:43PM +0100, David Howells wrote: > 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. Can you re-iterate the exact problem? I konw we talked about this in the past, but I seem to have misplaced those memories :/ FWIW I agree that kref is useless fluff, but I've long ago given up on that fight.