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=-8.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 F18B5C10F03 for ; Tue, 23 Apr 2019 20:03:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0EE1217D9 for ; Tue, 23 Apr 2019 20:03:52 +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="jrLd3Y5w" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727152AbfDWUDv (ORCPT ); Tue, 23 Apr 2019 16:03:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54228 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726043AbfDWUDv (ORCPT ); Tue, 23 Apr 2019 16:03:51 -0400 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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=hb01MqLnuP98D2RoWKX+a93Pok53youKonh3HoYDsEs=; b=jrLd3Y5wt7POd90HFccujSy1P g2LW4Kx6vLBasdOIk39IhEtAR+vKMpWNvC/qUjJtLAD2KK1XTEd/hWgJtWFVF0qvJPyk9BcHHD8Ud 6X21Ka944HdvU5Z1alWK1f3xohAYIt3vD6xuw1acxolv8NntxZxRC1j6/9GAMG8Pk/Y5vxUJ1XCd5 EMK1FvffGi4DO9apPX8xgcvbXQTNwEyh6IKCVQ9EkfndrxDQLXrJNSKLrh6Nhk6/kL+TCyehz3CNu +K9ygjXRT0utcnfqYMbup8BYm7iGcuA8vekmpvozmJZwhPvftpRCeYZgnYoB8J8DKP0fdMIo80XlK bd8qAjcuQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hJ1dQ-000135-2v; Tue, 23 Apr 2019 20:03:20 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D1A1329C30E18; Tue, 23 Apr 2019 22:03:18 +0200 (CEST) Date: Tue, 23 Apr 2019 22:03:18 +0200 From: Peter Zijlstra To: Waiman Long Cc: Linus Torvalds , Ingo Molnar , Will Deacon , Thomas Gleixner , Linux List Kernel Mailing , the arch/x86 maintainers , Davidlohr Bueso , Tim Chen , huang ying , Roman Gushchin , Alexei Starovoitov , Daniel Borkmann , Steven Rostedt Subject: [PATCH] trace: Fix preempt_enable_no_resched() abuse Message-ID: <20190423200318.GY14281@hirez.programming.kicks-ass.net> References: <20190419130304.GV14281@hirez.programming.kicks-ass.net> <20190419131522.GW14281@hirez.programming.kicks-ass.net> <57620139-92a3-4a21-56bd-5d6fff23214f@redhat.com> <7b1bfc26-6e90-bd65-ab46-08413acd80e9@redhat.com> <20190423141714.GO11158@hirez.programming.kicks-ass.net> <4f62d7f2-e5f6-500e-3e70-b1d1978f7140@redhat.com> <20190423193435.GX4038@hirez.programming.kicks-ass.net> <88ba7be0-9ec5-941e-1b3f-80fbe05fe3a0@redhat.com> <20190423195559.GY4038@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190423195559.GY4038@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 23, 2019 at 09:55:59PM +0200, Peter Zijlstra wrote: > On Tue, Apr 23, 2019 at 03:41:32PM -0400, Waiman Long wrote: > > I saw a number of instances of > > preempt_enable_no_resched() without right next a schedule(). > > Look more closely.. and let me know, if true, those are bugs that need > fixing. > > Argghhh.. BPF... /me shakes head, Steve... --- Subject: trace: Fix preempt_enable_no_resched() abuse Unless the very next line is schedule(), or implies it, one must not use preempt_enable_no_resched(). It can cause a preemption to go missing and thereby cause arbitrary delays, breaking the PREEMPT=y invariant. Cc: Steven Rostedt Fixes: 37886f6a9f62 ("ring-buffer: add api to allow a tracer to change clock source") Signed-off-by: Peter Zijlstra (Intel) --- kernel/trace/ring_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 41b6f96e5366..4ee8d8aa3d0f 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -762,7 +762,7 @@ u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu) preempt_disable_notrace(); time = rb_time_stamp(buffer); - preempt_enable_no_resched_notrace(); + preempt_enable_notrace(); return time; }