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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 8DE74C388F7 for ; Mon, 9 Nov 2020 13:20:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3849D208FE for ; Mon, 9 Nov 2020 13:20:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604928018; bh=yakpp09G5l4f/rE3il3+MK6ReUoTT/4nqVv32upIcAQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=L+r8a6hxKiIk9hwKGtGAH9qfygEn9hxsfBRJuUQpeaednycaNJuT9wSGNNlYowWUU +RMMjjFaa2qHsyJiDObt/2hbBNqlvpbq9zxOcCo3ospNo9IFqHy+RHN8QofmGvVG9q Q21ENhRoDomFFFzk2wvrUbV1FHlsC2cslzmBKCno= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387466AbgKINUQ (ORCPT ); Mon, 9 Nov 2020 08:20:16 -0500 Received: from mail.kernel.org ([198.145.29.99]:47704 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387894AbgKINUL (ORCPT ); Mon, 9 Nov 2020 08:20:11 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 77303206D8; Mon, 9 Nov 2020 13:20:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604928010; bh=yakpp09G5l4f/rE3il3+MK6ReUoTT/4nqVv32upIcAQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RFxPe38j7wcshKumIJtx/dJ03sNGacVlbB1Gir+wwOHP9bjCu52Spbfokj95D6Pcq n8KMBWC5CBZuLTv4KoUMvcurJGH1990PO7LHuA4TAFQfZ9Lx8Ci3oSQZjR0mB+aEZu Jo1C/CqAU14k8GABqZjtiwAqW37IA3V1X+1vbA8Q= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Steven Rostedt (VMware)" Subject: [PATCH 5.9 066/133] ftrace: Handle tracing when switching between context Date: Mon, 9 Nov 2020 13:55:28 +0100 Message-Id: <20201109125033.909766819@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201109125030.706496283@linuxfoundation.org> References: <20201109125030.706496283@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Steven Rostedt (VMware) commit 726b3d3f141fba6f841d715fc4d8a4a84f02c02a upstream. When an interrupt or NMI comes in and switches the context, there's a delay from when the preempt_count() shows the update. As the preempt_count() is used to detect recursion having each context have its own bit get set when tracing starts, and if that bit is already set, it is considered a recursion and the function exits. But if this happens in that section where context has changed but preempt_count() has not been updated, this will be incorrectly flagged as a recursion. To handle this case, create another bit call TRANSITION and test it if the current context bit is already set. Flag the call as a recursion if the TRANSITION bit is already set, and if not, set it and continue. The TRANSITION bit will be cleared normally on the return of the function that set it, or if the current context bit is clear, set it and clear the TRANSITION bit to allow for another transition between the current context and an even higher one. Cc: stable@vger.kernel.org Fixes: edc15cafcbfa3 ("tracing: Avoid unnecessary multiple recursion checks") Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.h | 23 +++++++++++++++++++++-- kernel/trace/trace_selftest.c | 9 +++++++-- 2 files changed, 28 insertions(+), 4 deletions(-) --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -636,6 +636,12 @@ enum { * function is called to clear it. */ TRACE_GRAPH_NOTRACE_BIT, + + /* + * When transitioning between context, the preempt_count() may + * not be correct. Allow for a single recursion to cover this case. + */ + TRACE_TRANSITION_BIT, }; #define trace_recursion_set(bit) do { (current)->trace_recursion |= (1<<(bit)); } while (0) @@ -690,8 +696,21 @@ static __always_inline int trace_test_an return 0; bit = trace_get_context_bit() + start; - if (unlikely(val & (1 << bit))) - return -1; + if (unlikely(val & (1 << bit))) { + /* + * It could be that preempt_count has not been updated during + * a switch between contexts. Allow for a single recursion. + */ + bit = TRACE_TRANSITION_BIT; + if (trace_recursion_test(bit)) + return -1; + trace_recursion_set(bit); + barrier(); + return bit + 1; + } + + /* Normal check passed, clear the transition to allow it again */ + trace_recursion_clear(TRACE_TRANSITION_BIT); val |= 1 << bit; current->trace_recursion = val; --- a/kernel/trace/trace_selftest.c +++ b/kernel/trace/trace_selftest.c @@ -492,8 +492,13 @@ trace_selftest_function_recursion(void) unregister_ftrace_function(&test_rec_probe); ret = -1; - if (trace_selftest_recursion_cnt != 1) { - pr_cont("*callback not called once (%d)* ", + /* + * Recursion allows for transitions between context, + * and may call the callback twice. + */ + if (trace_selftest_recursion_cnt != 1 && + trace_selftest_recursion_cnt != 2) { + pr_cont("*callback not called once (or twice) (%d)* ", trace_selftest_recursion_cnt); goto out; }