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=-0.6 required=3.0 tests=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 0E13EC433E0 for ; Mon, 25 May 2020 17:03:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF2A92073B for ; Mon, 25 May 2020 17:03:36 +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="ycGpn/y3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389298AbgEYRDg (ORCPT ); Mon, 25 May 2020 13:03:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388410AbgEYRDf (ORCPT ); Mon, 25 May 2020 13:03:35 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 536E2C061A0E; Mon, 25 May 2020 10:03:35 -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=XXwDcP3dcHVTH31ED3YGNDr9xfCF6QILoNLYHiAPWHo=; b=ycGpn/y3r7HAJ3xWO1uMSrRHOq JLE/YYhMxpqwJK3nsuVG+6K5dhNTriMLZElhL9QB8zWZoMxbANDlFN+YKMVMh8NGtg1lVaj//BsWS fZHpgKxDvyNSxJr/Zb1E2cpU2hfPk8zjKSk9ISh/TWl4JfvcIuYJqHQsy6Y1mj4J7UtjUmq+zpBH0 qjKvb9j9E26PZUWA4WMGnSLhN5Y2Xlof1vMPm2VU8sSrWekAH/wYNUyRyvPXVCNV98TmS8LNbtKEg M3GLYpoH/LF0BFp0NMdQyn8fP9fczpHO9vSI98EpIeMMRGAOvSR3TUUMHMbkeKsw4dfWnroWSyDd8 AqILb3BA==; 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 1jdGVB-0003k4-4V; Mon, 25 May 2020 17:03:01 +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 83142300B38; Mon, 25 May 2020 19:02:57 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6CC8220BD4F39; Mon, 25 May 2020 19:02:57 +0200 (CEST) Date: Mon, 25 May 2020 19:02:57 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Andrii Nakryiko , Alan Stern , parri.andrea@gmail.com, will@kernel.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "andrii.nakryiko@gmail.com" Subject: Re: Some -serious- BPF-related litmus tests Message-ID: <20200525170257.GA325280@hirez.programming.kicks-ass.net> References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> <20200522143201.GB32434@rowland.harvard.edu> <20200522174352.GJ2869@paulmck-ThinkPad-P72> <006e2bc6-7516-1584-3d8c-e253211c157e@fb.com> <20200525112521.GD317569@hirez.programming.kicks-ass.net> <20200525154730.GW2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200525154730.GW2869@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 25, 2020 at 08:47:30AM -0700, Paul E. McKenney wrote: > On Mon, May 25, 2020 at 01:25:21PM +0200, Peter Zijlstra wrote: > > That is; how can you use a spinlock on the producer side at all? > > So even trylock is now forbidden in NMI handlers? If so, why? The litmus tests don't have trylock. But you made me look at the actual patch: +static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) +{ + unsigned long cons_pos, prod_pos, new_prod_pos, flags; + u32 len, pg_off; + struct bpf_ringbuf_hdr *hdr; + + if (unlikely(size > RINGBUF_MAX_RECORD_SZ)) + return NULL; + + len = round_up(size + BPF_RINGBUF_HDR_SZ, 8); + cons_pos = smp_load_acquire(&rb->consumer_pos); + + if (in_nmi()) { + if (!spin_trylock_irqsave(&rb->spinlock, flags)) + return NULL; + } else { + spin_lock_irqsave(&rb->spinlock, flags); + } And that is of course utter crap. That's like saying you don't care about your NMI data.