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=-10.5 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 B533AC4363A for ; Mon, 5 Oct 2020 15:31:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CB9C2074F for ; Mon, 5 Oct 2020 15:31:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601911894; bh=2GjSQPTuaB7TWlIdz4/eFf2g6Be55yicyNCrJRNW1j8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=v1xPMcS41F0/VKAprRh6vPFlPSbD469w7guELdApoIbKRNmVVzMiOhINJxqZwXikn /OfV2iI9lXinpOljvYGQlc4lJXrixB79Ts76W2ndyjwt27af+cX5mY5Hu55zZi/r7q 2PYw6PkrW0v6nxqO+DfdwUggt04gZUw20NYJDUBU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727891AbgJEPbd (ORCPT ); Mon, 5 Oct 2020 11:31:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:58474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727382AbgJEPb3 (ORCPT ); Mon, 5 Oct 2020 11:31:29 -0400 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 B237C2085B; Mon, 5 Oct 2020 15:31:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601911889; bh=2GjSQPTuaB7TWlIdz4/eFf2g6Be55yicyNCrJRNW1j8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qt2YJLhKNp45Ah6xfMU1QWKsdu+uJ86ZhO1znXXiuu9RHkEjyHTrNJVFVaH1thICL 0cs6NSBQsj/kzTXilAo3AjKZBOzvNobN/ohd9D8Cn4CXJXd06tY8MEvFa6mP8v35v6 q2SBIpVsaS0qA6l6rpTxmuXCW1zqI26gbmmcZqog= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Paul McKenney , "Peter Zijlstra (Intel)" , "Steven Rostedt (VMware)" Subject: [PATCH 5.8 19/85] ftrace: Move RCU is watching check after recursion check Date: Mon, 5 Oct 2020 17:26:15 +0200 Message-Id: <20201005142115.662558364@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201005142114.732094228@linuxfoundation.org> References: <20201005142114.732094228@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 b40341fad6cc2daa195f8090fd3348f18fff640a upstream. The first thing that the ftrace function callback helper functions should do is to check for recursion. Peter Zijlstra found that when "rcu_is_watching()" had its notrace removed, it caused perf function tracing to crash. This is because the call of rcu_is_watching() is tested before function recursion is checked and and if it is traced, it will cause an infinite recursion loop. rcu_is_watching() should still stay notrace, but to prevent this should never had crashed in the first place. The recursion prevention must be the first thing done in callback functions. Link: https://lore.kernel.org/r/20200929112541.GM2628@hirez.programming.kicks-ass.net Cc: stable@vger.kernel.org Cc: Paul McKenney Fixes: c68c0fa293417 ("ftrace: Have ftrace_ops_get_func() handle RCU and PER_CPU flags too") Acked-by: Peter Zijlstra (Intel) Reported-by: Peter Zijlstra (Intel) Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ftrace.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6877,16 +6877,14 @@ static void ftrace_ops_assist_func(unsig { int bit; - if ((op->flags & FTRACE_OPS_FL_RCU) && !rcu_is_watching()) - return; - bit = trace_test_and_set_recursion(TRACE_LIST_START, TRACE_LIST_MAX); if (bit < 0) return; preempt_disable_notrace(); - op->func(ip, parent_ip, op, regs); + if (!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching()) + op->func(ip, parent_ip, op, regs); preempt_enable_notrace(); trace_clear_recursion(bit);