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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7062AC433EF for ; Thu, 3 Feb 2022 20:32:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354734AbiBCUcv (ORCPT ); Thu, 3 Feb 2022 15:32:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354538AbiBCUbs (ORCPT ); Thu, 3 Feb 2022 15:31:48 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9B9DFC061795; Thu, 3 Feb 2022 12:31:42 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6033EB835AA; Thu, 3 Feb 2022 20:31:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1EEFFC340E8; Thu, 3 Feb 2022 20:31:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643920300; bh=gr4hxJsFwjXa6Hnqo/BSb8MBYbytSgyQNkmjcvloyLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iAH5XvKpopFp6Rt3Sn2AqDNPfk/PoAsa/pNm4pD3Mt1WkiNVxPetMRlihhu66BSCT cbwPu8EWdbHnh7AevW2jCQbqFQYqeZMv1nwZCEYIGORhIoWjMCsgO21ThhAcjmv3RO wkwOsJhypF2Z0WepfaJiB73y7/uRVId1pAFmt9S1+H03a2ikoUbNwhb2ZtmqqQNy5C lhPL/Zrdw6G966GxUQCfNKeHWmn3WDsoXhLFqz97R41FDS6erWjmDWBaLkUtzZ1ab3 A+7vroCi1jj8oMNqrYdWF32ZVkLxQ01cOpogrDJRB3L/2BEbtg3R4BS0LR44KTcN6a ohZrn7u8PvAnw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: James Clark , Ruben Ayrapetyan , Peter Zijlstra , Sasha Levin , mingo@redhat.com, acme@kernel.org, linux-perf-users@vger.kernel.org Subject: [PATCH AUTOSEL 5.16 42/52] perf: Always wake the parent event Date: Thu, 3 Feb 2022 15:29:36 -0500 Message-Id: <20220203202947.2304-42-sashal@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220203202947.2304-1-sashal@kernel.org> References: <20220203202947.2304-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org From: James Clark [ Upstream commit 961c39121759ad09a89598ec4ccdd34ae0468a19 ] When using per-process mode and event inheritance is set to true, forked processes will create a new perf events via inherit_event() -> perf_event_alloc(). But these events will not have ring buffers assigned to them. Any call to wakeup will be dropped if it's called on an event with no ring buffer assigned because that's the object that holds the wakeup list. If the child event is disabled due to a call to perf_aux_output_begin() or perf_aux_output_end(), the wakeup is dropped leaving userspace hanging forever on the poll. Normally the event is explicitly re-enabled by userspace after it wakes up to read the aux data, but in this case it does not get woken up so the event remains disabled. This can be reproduced when using Arm SPE and 'stress' which forks once before running the workload. By looking at the list of aux buffers read, it's apparent that they stop after the fork: perf record -e arm_spe// -vvv -- stress -c 1 With this patch applied they continue to be printed. This behaviour doesn't happen when using systemwide or per-cpu mode. Reported-by: Ruben Ayrapetyan Signed-off-by: James Clark Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20211206113840.130802-2-james.clark@arm.com Signed-off-by: Sasha Levin --- kernel/events/core.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 63f0414666438..0b0655f4d0126 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5934,6 +5934,8 @@ static void ring_buffer_attach(struct perf_event *event, struct perf_buffer *old_rb = NULL; unsigned long flags; + WARN_ON_ONCE(event->parent); + if (event->rb) { /* * Should be impossible, we set this when removing @@ -5991,6 +5993,9 @@ static void ring_buffer_wakeup(struct perf_event *event) { struct perf_buffer *rb; + if (event->parent) + event = event->parent; + rcu_read_lock(); rb = rcu_dereference(event->rb); if (rb) { @@ -6004,6 +6009,9 @@ struct perf_buffer *ring_buffer_get(struct perf_event *event) { struct perf_buffer *rb; + if (event->parent) + event = event->parent; + rcu_read_lock(); rb = rcu_dereference(event->rb); if (rb) { @@ -6703,7 +6711,7 @@ static unsigned long perf_prepare_sample_aux(struct perf_event *event, if (WARN_ON_ONCE(READ_ONCE(sampler->oncpu) != smp_processor_id())) goto out; - rb = ring_buffer_get(sampler->parent ? sampler->parent : sampler); + rb = ring_buffer_get(sampler); if (!rb) goto out; @@ -6769,7 +6777,7 @@ static void perf_aux_sample_output(struct perf_event *event, if (WARN_ON_ONCE(!sampler || !data->aux_size)) return; - rb = ring_buffer_get(sampler->parent ? sampler->parent : sampler); + rb = ring_buffer_get(sampler); if (!rb) return; -- 2.34.1