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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED,USER_AGENT_GIT 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 4C062C28CC5 for ; Sat, 8 Jun 2019 11:50:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20065216C4 for ; Sat, 8 Jun 2019 11:50:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994655; bh=nqQNnz0bhuscTheDh1ia2yZgdTB90L1LseANxOmAMYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=GEeZ5v3ifsGGCJHaAlmxV2N70R0k8KJCqZUscj3AynsNTA2AB1+pKqhpNE0JeVw7n 2FI/s6H29nmRvaZAsKkvXI0b4dmoEru3ciwLqzcxN8OvkB0Td844Ec/ROP5TNvYdaR TfHhMasiEaYw6Dazil9Znu2ZuvDdhhWSuArdR26s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729563AbfFHLuy (ORCPT ); Sat, 8 Jun 2019 07:50:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:37054 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729561AbfFHLsU (ORCPT ); Sat, 8 Jun 2019 07:48:20 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B9CFC21537; Sat, 8 Jun 2019 11:48:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994499; bh=nqQNnz0bhuscTheDh1ia2yZgdTB90L1LseANxOmAMYk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KznWKOKWtTrjHq17XWvmIThqK6pHA2qWpqBQWhSr8ko0fc+kFGuO7KY0eMiq16BL6 RED9uuhOTSLttG3jU7Y3mx7vQK5aPJsf9PCra0nz+wUtn+pHap+wYE5+H18YyIqPP1 MKEcKh962kxc+soujDWP2z5ZyKmOahexRYDFfJ/o= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Zijlstra , Yabin Cui , Alexander Shishkin , Arnaldo Carvalho de Melo , Jiri Olsa , Linus Torvalds , Stephane Eranian , Thomas Gleixner , Vince Weaver , acme@kernel.org, mark.rutland@arm.com, namhyung@kernel.org, Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.9 06/20] perf/ring_buffer: Add ordering to rb->nest increment Date: Sat, 8 Jun 2019 07:47:42 -0400 Message-Id: <20190608114756.9742-6-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190608114756.9742-1-sashal@kernel.org> References: <20190608114756.9742-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ Upstream commit 3f9fbe9bd86c534eba2faf5d840fd44c6049f50e ] Similar to how decrementing rb->next too early can cause data_head to (temporarily) be observed to go backward, so too can this happen when we increment too late. This barrier() ensures the rb->head load happens after the increment, both the one in the 'goto again' path, as the one from perf_output_get_handle() -- albeit very unlikely to matter for the latter. Suggested-by: Yabin Cui Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Cc: mark.rutland@arm.com Cc: namhyung@kernel.org Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables") Link: http://lkml.kernel.org/r/20190517115418.309516009@infradead.org Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/events/ring_buffer.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 524744a38d61..8e8b903b7613 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -49,6 +49,15 @@ static void perf_output_put_handle(struct perf_output_handle *handle) unsigned long head; again: + /* + * In order to avoid publishing a head value that goes backwards, + * we must ensure the load of @rb->head happens after we've + * incremented @rb->nest. + * + * Otherwise we can observe a @rb->head value before one published + * by an IRQ/NMI happening between the load and the increment. + */ + barrier(); head = local_read(&rb->head); /* -- 2.20.1