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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 90D87C49ECA for ; Thu, 6 Aug 2020 11:05:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8590323103 for ; Thu, 6 Aug 2020 11:05:24 +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="WDwoXxOe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728952AbgHFIfx (ORCPT ); Thu, 6 Aug 2020 04:35:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51822 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726844AbgHFIfw (ORCPT ); Thu, 6 Aug 2020 04:35:52 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 94971C061574 for ; Thu, 6 Aug 2020 01:35:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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; bh=KLCbXXU3FEEkK2kFGOqzvm7OFPwa7d/ljqwYmaL9Dxo=; b=WDwoXxOenowP410hrcgMlpdl3V Pl2Yw8sVwgsENBuDhkRA0zoEPM6tr+5AfwhbYty1pl/vVfOjfPo61tpZ6kDZXOCHx4qgOktdWVtUV wo3lZ7tZ0QEkrz1mdWlKVIC40ubRLWzaEO4HNrPAdq0BXR1Z+YcHmBgfFYI1hbGyqC2Ttofiv1a/y gh+iZ1YfyeCJutQ/3ePjmqM/rcvtkg6q6IJEjRnT8i67uvXYp/QCJ2rZdFFPqT/e3NF6UnaANVX4A 7BXY2tbdXOX+jstBC4BXUOuhUd2bx5lNSGEcsWhUK7YSAKknG4hu4pfHPi1Am7i7/+FfMkxPaC/ez Yr/T9G2g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k3bN9-0002f7-A0; Thu, 06 Aug 2020 08:35:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 50E0A300446; Thu, 6 Aug 2020 10:35:30 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DB8802B61F1C0; Thu, 6 Aug 2020 10:35:30 +0200 (CEST) Date: Thu, 6 Aug 2020 10:35:30 +0200 From: peterz@infradead.org To: Alexander Shishkin Cc: Arnaldo Carvalho de Melo , Ingo Molnar , linux-kernel@vger.kernel.org, Jiri Olsa , alexey.budankov@linux.intel.com, adrian.hunter@intel.com, Andi Kleen Subject: Re: [PATCH 1/2] perf: Add closing sibling events' file descriptors Message-ID: <20200806083530.GV2674@hirez.programming.kicks-ass.net> References: <20200708151635.81239-1-alexander.shishkin@linux.intel.com> <20200708151635.81239-2-alexander.shishkin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200708151635.81239-2-alexander.shishkin@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 08, 2020 at 06:16:34PM +0300, Alexander Shishkin wrote: > Currently, perf requires one file descriptor per event. In large groups, > this may mean running into the limit on open file descriptors. However, > the sibling events in a group only need file descriptors for the initial > configuration stage, after which they may not be needed any more. > > This adds an opt-in flag to the perf_event_open() syscall to retain > sibling events after their file descriptors are closed. In this case, the > actual events will be closed with the group leader. So having the 1:1 relation with filedesc imposes a resource limit on userspace. This patch breaks that and enables a user to basically DoS the system by creating unbound events.