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=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=ham 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 7FF93C433DF for ; Fri, 21 Aug 2020 08:58:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C05A207DF for ; Fri, 21 Aug 2020 08:58:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="q2mTGHNb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728421AbgHUI6Q (ORCPT ); Fri, 21 Aug 2020 04:58:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727780AbgHUI6Q (ORCPT ); Fri, 21 Aug 2020 04:58:16 -0400 Received: from mail-oi1-x244.google.com (mail-oi1-x244.google.com [IPv6:2607:f8b0:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D6AB2C061386 for ; Fri, 21 Aug 2020 01:58:15 -0700 (PDT) Received: by mail-oi1-x244.google.com with SMTP id o21so935004oie.12 for ; Fri, 21 Aug 2020 01:58:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BIVvoIxDscazkjxDxxPv5gvsunWCC5y5O+yvu3GA8zk=; b=q2mTGHNbZxMuit35p7qTafE3TeI5U4AIiwPe1TCQ60Bg1PNbHBQqxARTxJFakOXvBL EYL6UddvN/5PCURTSIoAebx15zIp/0ZbhZoxJPaEJlBiCR6YJuDEhuTz/pVEhqzHUmV6 Ajtl9cLGPJLFG+SWjhjUBiHV8nk168vuEKXkilrXxA37Bdi/32/TnZCX8Atkn80dhR44 Ji7uf9nJ5vTxBXu/whaj64aGyMA6jXeq/1rdeneA1W33lpiCnqvq07WArSTYz+lhbwC9 U67GIy4wP+RIVPN9WE3SKEUGnaGheHwgAI6PB7EtT2wHLWeW53MoGB4nth+aYtJAjIkh TmDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BIVvoIxDscazkjxDxxPv5gvsunWCC5y5O+yvu3GA8zk=; b=pFJP8W3YWNus2XYnJV6EudyCYN53D9eEGI5oUZ7ydojXXzecO4oqo3YLCDN0aSdmev h0yELcIL3qdDGJtcoKKMldyxomdWNWBZiF4s9iZtCFVhMCLwew8zX8AMWd+vZykJCvLV fOKRrvB/VPWWGClt65fo/ksHbedk4Ze/tb01z3AZpEHoDrvsoVTUh5gSS9Xgo4Bg5V9P YAWMj1OQecIC2QbWf8ayb0HKO2rzqwOiZ5GpVAcs0Z06Z30OdxTNmGeSKj9JFCHHl+U+ QPrQbKhX9Y1NnIIBytmp/8ZvSqcUVmVDAHNx/eCQ86Bke9ILVuf5xczn41KcQt1ZVlF4 XpfA== X-Gm-Message-State: AOAM531k/yqt7Lv+Or0aoHZHoWEF2NVvhRqeV1hicLh7v7qV/4hmYts5 WzTCgdPGiB2e9rbR5dOjQFTQHPWzvxJ7MuVkp2r4xw== X-Google-Smtp-Source: ABdhPJz9iTT3XBj8WRl+ZOCH4zNT0K/w11yAgDx5v19ejdo/Cy91vQs/Hr3vXSnSxwgC/L4S0ps04S39NWudNp4fubQ= X-Received: by 2002:aca:d4d5:: with SMTP id l204mr1175616oig.70.1598000294457; Fri, 21 Aug 2020 01:58:14 -0700 (PDT) MIME-Version: 1.0 References: <20200821063043.1949509-1-elver@google.com> In-Reply-To: <20200821063043.1949509-1-elver@google.com> From: Marco Elver Date: Fri, 21 Aug 2020 10:58:02 +0200 Message-ID: Subject: Re: [PATCH] random32: Use rcuidle variant for tracepoint To: Marco Elver Cc: LKML , "David S. Miller" , kuba@kernel.org, Netdev , Steven Rostedt , Eric Dumazet , Peter Zijlstra , "Paul E. McKenney" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 21 Aug 2020 at 08:30, Marco Elver wrote: > With KCSAN enabled, prandom_u32() may be called from any context, > including idle CPUs. > > Therefore, switch to using trace_prandom_u32_rcuidle(), to avoid various > issues due to recursion and lockdep warnings when KCSAN and tracing is > enabled. > > Fixes: 94c7eb54c4b8 ("random32: add a tracepoint for prandom_u32()") > Link: https://lkml.kernel.org/r/20200820155923.3d5c4873@oasis.local.home > Suggested-by: Steven Rostedt > Signed-off-by: Marco Elver > Cc: Eric Dumazet > Cc: Peter Zijlstra > --- > lib/random32.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/random32.c b/lib/random32.c > index 932345323af0..1c5607a411d4 100644 > --- a/lib/random32.c > +++ b/lib/random32.c > @@ -83,7 +83,7 @@ u32 prandom_u32(void) > u32 res; > > res = prandom_u32_state(state); > - trace_prandom_u32(res); > + trace_prandom_u32_rcuidle(res); > put_cpu_var(net_rand_state); > Note that, for KCSAN's use, there is still a small chance this will mess things up. So, as a short-term fix, I'd appreciate if this patch will be applied to 5.9, assuming it doesn't mess with the original usecase. Longer-term, I think I need to switch KCSAN to use either prandom_u32_state() or open-code its own prandom function, as the trace-rcuidle code calls into srcu, which might have other weird effects if KCSAN instruments that. Still working on the longer-term fix. Thanks, -- Marco