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 9C419C28CC5 for ; Sat, 8 Jun 2019 11:52:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 75B2D214AE for ; Sat, 8 Jun 2019 11:52:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994737; bh=ugUySFmSmxgk0l+L3c6rCvDBw8Ve0Z51DyJfgMwjbVo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=TjpVBzckOQGD94kvIxRfALUeACJTiiZ+GpLPq6m+ZOfKWs5PbU/RI65tbw0JMH4hG vnCJbmZyfGRj7Qtdawgh87TQcWEXG0SC9K2UVWbUgGYbdJ+ZqIXqO8Eun4X94RYRqx 5HErBXM4mHTNRAekaw8yH7v8Dhu60iRk9k/3wGog= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729933AbfFHLwQ (ORCPT ); Sat, 8 Jun 2019 07:52:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:35964 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728913AbfFHLrS (ORCPT ); Sat, 8 Jun 2019 07:47:18 -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 DCADA21537; Sat, 8 Jun 2019 11:47:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994437; bh=ugUySFmSmxgk0l+L3c6rCvDBw8Ve0Z51DyJfgMwjbVo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=V72MzVUcJt+MLUHcO4R3pOwtXy3igbGsQ/ewe7yiV5G2vnBkH+YjEX53bDoqcR12G DSKCFE/NoVLWGFVZ3MfDOSE1TywHZaklT8jQ1vFP9dW7hqhE96dYp2LLgn11EWFL7Y ZIQ/muxVhJw+BOeKGa4nzgzyGKUqiwgUOoAP+ccA= 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 4.14 11/31] perf/ring_buffer: Add ordering to rb->nest increment Date: Sat, 8 Jun 2019 07:46:22 -0400 Message-Id: <20190608114646.9415-11-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190608114646.9415-1-sashal@kernel.org> References: <20190608114646.9415-1-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 fde853270c09..aef2af80a927 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