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 520D5C28CC5 for ; Sat, 8 Jun 2019 11:54:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 280E721537 for ; Sat, 8 Jun 2019 11:54:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994877; bh=/x2IvdJn9NvVakt26+r+XW9NQseQytvoZGiShE3R6NI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sxf9sfPKuXrOuGb2E6w3waJwolSPEMB2GznRzdtGOttbH6uf7c56mG0170p01M9gW CROFXYy2yY5skrBuzDadldNPh+hfg1+ghA2aNDF/lDF87LAcQlDvhnHgiuAZ8pUdIQ prvXs+9E7e0Wz0JkeuDdaqGAZ+mO/dGql9cVTABA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729365AbfFHLyg (ORCPT ); Sat, 8 Jun 2019 07:54:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:57648 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727571AbfFHLk0 (ORCPT ); Sat, 8 Jun 2019 07:40:26 -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 B4B99214C6; Sat, 8 Jun 2019 11:40:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559994026; bh=/x2IvdJn9NvVakt26+r+XW9NQseQytvoZGiShE3R6NI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Q5JGwM3FMFjm4scCx++WPOs69iuZdB+CIquV7EnsNaQaeIPrJ2qPimF+SBN6I/P+C GnCDqiW14qjDL7EoKVhi+2Ccf8wmnb3FBcyyrSgKNhqtpx8Tj8PpPevGh7i3RkVN2E CDJGJA69C281zcT5b5fWjuG/X8SquefsxfSCr1+c= 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 5.1 22/70] perf/ring_buffer: Add ordering to rb->nest increment Date: Sat, 8 Jun 2019 07:39:01 -0400 Message-Id: <20190608113950.8033-22-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190608113950.8033-1-sashal@kernel.org> References: <20190608113950.8033-1-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 009467a60578..4b5f8d932400 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -48,6 +48,15 @@ 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