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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 47B77C04ABB for ; Thu, 13 Sep 2018 07:07:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DAC9F20881 for ; Thu, 13 Sep 2018 07:07:47 +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="UU9ADuox" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DAC9F20881 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727773AbeIMMPz (ORCPT ); Thu, 13 Sep 2018 08:15:55 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:45012 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726694AbeIMMPy (ORCPT ); Thu, 13 Sep 2018 08:15:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=N/5C/eSkvq9wDSxmWyO/AV8RAlyLbGlkAF5j9oMFunI=; b=UU9ADuoxk8zQP8E4mZt7Kxul2 llg5BJ4m9TzNJRigHc90ZVVaA80xLzxcF6mkUFSURI2hMwE2VYhyfC1Dam+/yYHXxicCHz0YV/UqN i1Vdxk9NPg0VsjVrHHaEofVP6dUjG8Doyf8q/eIYTmRU8L3LFQ1Tei97TnJROlooNt28v1SyQ9H9A H8qGfNrXYDQsutVr7HyMB7/rsADKEac/E6ng12PH9jzyIbxg64/6jXP1ZzzMzaaIeUoUz9KtrZ1Oo fXdN2ikXv6xnd1zIpY4hYuhxQqKrm8TUAs2gsfYT6Mz09A1MLH5PIBgQAKI5vcelnjDSo6aPr2Q44 97T35OYCA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g0Lj5-0000eN-5C; Thu, 13 Sep 2018 07:07:43 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DEED0202B2E3B; Thu, 13 Sep 2018 09:07:40 +0200 (CEST) Date: Thu, 13 Sep 2018 09:07:40 +0200 From: Peter Zijlstra To: Jiri Olsa Cc: Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Namhyung Kim , Alexander Shishkin , Andi Kleen Subject: Re: [PATCH] perf: Prevent recursion in ring buffer Message-ID: <20180913070740.GT24124@hirez.programming.kicks-ass.net> References: <20180912193317.10339-1-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180912193317.10339-1-jolsa@kernel.org> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 12, 2018 at 09:33:17PM +0200, Jiri Olsa wrote: > Some of the scheduling tracepoints allow the perf_tp_event > code to write to ring buffer under different cpu than the > code is running on. ARGH.. that is indeed borken. > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > index 4a9937076331..0c976ac414c5 100644 > --- a/kernel/events/ring_buffer.c > +++ b/kernel/events/ring_buffer.c > @@ -101,6 +101,7 @@ static void perf_output_put_handle(struct perf_output_handle *handle) > > out: > preempt_enable(); > + atomic_set(&rb->recursion, 0); > } > > static __always_inline bool > @@ -145,6 +146,12 @@ __perf_output_begin(struct perf_output_handle *handle, > goto out; > } > > + if (atomic_cmpxchg(&rb->recursion, 0, 1) != 0) { > + if (rb->nr_pages) > + local_inc(&rb->lost); > + goto out; > + } > + > handle->rb = rb; > handle->event = event; > > @@ -286,6 +293,7 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) > rb->overwrite = 1; > > atomic_set(&rb->refcount, 1); > + atomic_set(&rb->recursion, 0); > > INIT_LIST_HEAD(&rb->event_list); > spin_lock_init(&rb->event_lock); That's not a recursion count, that's a test-and-set spinlock, and you got the memory ordering wrong for that. Also, we tried very hard to avoid atomic ops in the ring-buffer and you just wrecked that. Worse, you wrecked previously working interrupt nesting output. Let me have a look at this.