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[23.128.96.18]) by mx.google.com with ESMTP id l25si373395edj.169.2020.10.05.09.53.42; Mon, 05 Oct 2020 09:54:05 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=JId0cWBy; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727738AbgJEPaP (ORCPT + 99 others); Mon, 5 Oct 2020 11:30:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:56090 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727196AbgJEP3z (ORCPT ); Mon, 5 Oct 2020 11:29:55 -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 BD5972074F; Mon, 5 Oct 2020 15:29:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601911794; bh=WoWbLR6+CiYttAimAaClfSgg3I1hyBP75BXPrz+J8yw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JId0cWByyWEhhGUXf5SKPZauezYlsXpARSuUunIat/OWcvJYYYv7qgAx+1WfQCT7m xKRGi55b8xt5VLD69dSgPw/clHPejSa7iQF7rCBPOf3a9dEhQVBT32Rf0bDh7Ehz94 +wAMpxw3Xd4rEZBfoRw1FfHD1t++j7rCLWVQNc00= 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 5.4 13/57] ftrace: Move RCU is watching check after recursion check Date: Mon, 5 Oct 2020 17:26:25 +0200 Message-Id: <20201005142110.435571437@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201005142109.796046410@linuxfoundation.org> References: <20201005142109.796046410@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 @@ -6382,16 +6382,14 @@ 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);