From nobody Thu Sep 18 12:52:13 2025 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 C9E37C4708E for ; Tue, 6 Dec 2022 02:50:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230154AbiLFCur (ORCPT ); Mon, 5 Dec 2022 21:50:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232481AbiLFCuo (ORCPT ); Mon, 5 Dec 2022 21:50:44 -0500 Received: from mail-pf1-x42e.google.com (mail-pf1-x42e.google.com [IPv6:2607:f8b0:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21EF532D for ; Mon, 5 Dec 2022 18:50:43 -0800 (PST) Received: by mail-pf1-x42e.google.com with SMTP id g1so5240712pfk.2 for ; Mon, 05 Dec 2022 18:50:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=WEYJ73xbUUTuiFPUB3TgsG4oZgIHBL7beR0oFU4cLiY=; b=OKVs83b4UGUNN2j1s6jwUm405BVfAXXNGOO/1BbcrtZTAmY2VCR5rAvmq51plcpn4W rp1bENJ7GEKvgmumqJTFWD8sRRG9wP2U2feDEBgbwQAVyrkh4ooiPK8/uYsb+HBJoAMv Ujxq+sjw5VSueKFqN0CCjj6UQ9fXtyA3XX7qdlD0BnZj0IafZ9h+YcaseoJBydEd8rp8 G6EMWuEEuAp4Hv+oikWoaGVDEV//dQqb9hiykO4O3VIhbTRF42tcJgWMT9u8weSYGMY3 uuWwmZ8KBepsLO1DBrslBCTZQ8yy28zfbxn35DkgV4QTYxcfbsFIKEpdWsKgrH3C14h6 1dUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=WEYJ73xbUUTuiFPUB3TgsG4oZgIHBL7beR0oFU4cLiY=; b=wAWIbHVXXV9kY1XJbwkOsdKTlVUiP4841Lj2QbjLij1UGjE1i9Szx6gtdSTxioQPs4 SRgTzOHUgcoydN5DQFJqsIXZ5H8lBaPc7qClupxC3SqJbtyYSp0YlZDEB6qcQJQ1DZRs wYgbMcIaLAa9qu4bqWPXG+waOUoeynH5pvWpEWqe7uferlrmfjGsaIxYrjZGbftDqoC9 LHXt+OkBcKAqaMuRCcMct9rroSmpI7rG/Cq+d98YOa2CdyoZvUWZ3y3KUgN6sXvpfOC8 xVH+mqaeDkEOPnfrXLU+h+bYVu9StmG7yGI49iNxegNq1YW4YZuzDgCbsSanmezDiV5Z uUSw== X-Gm-Message-State: ANoB5pm8Vi6GwSWsdQ/JidCBP0LJmZrGSovNd/Og48hZCeW5PA4aaI6L WQ+f8/l20aUjZR6qCto2syMPXA== X-Google-Smtp-Source: AA0mqf4bzqGZRywxJ9QXKAqa/GtPKIMErbmBEYPJOTEm/8DTgmSWLgq5+wobqCf0pQxYyGLrYS7SxA== X-Received: by 2002:a05:6a00:2883:b0:572:7b49:4f47 with SMTP id ch3-20020a056a00288300b005727b494f47mr69791918pfb.16.1670295042616; Mon, 05 Dec 2022 18:50:42 -0800 (PST) Received: from C02CV1DAMD6P.bytedance.net ([139.177.225.255]) by smtp.gmail.com with ESMTPSA id c73-20020a624e4c000000b0056bc742d21esm10892043pfb.176.2022.12.05.18.50.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Dec 2022 18:50:42 -0800 (PST) From: Chengming Zhou To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Chengming Zhou Subject: [PATCH] perf/core: Fix cgroup events tracking Date: Tue, 6 Dec 2022 10:50:34 +0800 Message-Id: <20221206025034.75125-1-zhouchengming@bytedance.com> X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" We encounter perf warnings when using cgroup events like: ``` cd /sys/fs/cgroup mkdir test perf stat -e cycles -a -G test ``` WARNING: CPU: 0 PID: 690 at kernel/events/core.c:849 perf_cgroup_switch+0xb= 2/0xc0 [ 91.393417] Call Trace: [ 91.393772] [ 91.394080] __schedule+0x4ae/0x9f0 [ 91.394535] ? _raw_spin_unlock_irqrestore+0x23/0x40 [ 91.395145] ? __cond_resched+0x18/0x20 [ 91.395622] preempt_schedule_common+0x2d/0x70 [ 91.396163] __cond_resched+0x18/0x20 [ 91.396621] wait_for_completion+0x2f/0x160 [ 91.397137] ? cpu_stop_queue_work+0x9e/0x130 [ 91.397665] affine_move_task+0x18a/0x4f0 WARNING: CPU: 0 PID: 690 at kernel/events/core.c:829 ctx_sched_in+0x1cf/0x1= e0 [ 91.430151] Call Trace: [ 91.430490] [ 91.430793] ? ctx_sched_out+0xb7/0x1b0 [ 91.431274] perf_cgroup_switch+0x88/0xc0 [ 91.431778] __schedule+0x4ae/0x9f0 [ 91.432215] ? _raw_spin_unlock_irqrestore+0x23/0x40 [ 91.432825] ? __cond_resched+0x18/0x20 [ 91.433299] preempt_schedule_common+0x2d/0x70 [ 91.433839] __cond_resched+0x18/0x20 [ 91.434298] wait_for_completion+0x2f/0x160 [ 91.434808] ? cpu_stop_queue_work+0x9e/0x130 [ 91.435334] affine_move_task+0x18a/0x4f0 The above two warnings are not complete here since I remove other unimportant information. The problem is caused by the perf cgroup events tracking: CPU0 CPU1 perf_event_open() perf_event_alloc() account_event() account_event_cpu() atomic_inc(perf_cgroup_events) __perf_event_task_sched_out() if (atomic_read(perf_cgroup_events)) perf_cgroup_switch() // kernel/events/core.c:849 WARN_ON_ONCE(cpuctx->ctx.nr_cgroups =3D=3D 0) if (READ_ONCE(cpuctx->cgrp) =3D=3D cgrp) // false return perf_ctx_lock() ctx_sched_out() cpuctx->cgrp =3D cgrp ctx_sched_in() perf_cgroup_set_timestamp() // kernel/events/core.c:829 WARN_ON_ONCE(!ctx->nr_cgroups) perf_ctx_unlock() perf_install_in_context() add_event_to_ctx() list_add_event() perf_cgroup_event_enable() ctx->nr_cgroups++ cpuctx->cgrp =3D X We can see from above that we wrongly use percpu atomic perf_cgroup_events to check if we need to perf_cgroup_switch(), which should only be used when we know this CPU has cgroup events enabled. The commit bd2756811766 ("perf: Rewrite core context handling") change to have only one context per-CPU, so we can just use cpuctx->cgrp to check if this CPU has cgroup events enabled. So percpu atomic perf_cgroup_events is not needed. Signed-off-by: Chengming Zhou Tested-by: Ravi Bangoria --- kernel/events/core.c | 42 ++++++++++-------------------------------- 1 file changed, 10 insertions(+), 32 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index eacc3702654d..5d97a9f26003 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -380,7 +380,6 @@ enum event_type_t { =20 /* * perf_sched_events : >0 events exist - * perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu */ =20 static void perf_sched_delayed(struct work_struct *work); @@ -389,7 +388,6 @@ static DECLARE_DELAYED_WORK(perf_sched_work, perf_sched= _delayed); static DEFINE_MUTEX(perf_sched_mutex); static atomic_t perf_sched_count; =20 -static DEFINE_PER_CPU(atomic_t, perf_cgroup_events); static DEFINE_PER_CPU(struct pmu_event_list, pmu_sb_events); =20 static atomic_t nr_mmap_events __read_mostly; @@ -844,9 +842,16 @@ static void perf_cgroup_switch(struct task_struct *tas= k) struct perf_cpu_context *cpuctx =3D this_cpu_ptr(&perf_cpu_context); struct perf_cgroup *cgrp; =20 - cgrp =3D perf_cgroup_from_task(task, NULL); + /* + * cpuctx->cgrp is set when the first cgroup event enabled, + * and is cleared when the last cgroup event disabled. + */ + if (READ_ONCE(cpuctx->cgrp) =3D=3D NULL) + return; =20 WARN_ON_ONCE(cpuctx->ctx.nr_cgroups =3D=3D 0); + + cgrp =3D perf_cgroup_from_task(task, NULL); if (READ_ONCE(cpuctx->cgrp) =3D=3D cgrp) return; =20 @@ -3631,8 +3636,7 @@ void __perf_event_task_sched_out(struct task_struct *= task, * to check if we have to switch out PMU state. * cgroup event are system-wide mode only */ - if (atomic_read(this_cpu_ptr(&perf_cgroup_events))) - perf_cgroup_switch(next); + perf_cgroup_switch(next); } =20 static bool perf_less_group_idx(const void *l, const void *r) @@ -4974,15 +4978,6 @@ static void unaccount_pmu_sb_event(struct perf_event= *event) detach_sb_event(event); } =20 -static void unaccount_event_cpu(struct perf_event *event, int cpu) -{ - if (event->parent) - return; - - if (is_cgroup_event(event)) - atomic_dec(&per_cpu(perf_cgroup_events, cpu)); -} - #ifdef CONFIG_NO_HZ_FULL static DEFINE_SPINLOCK(nr_freq_lock); #endif @@ -5048,8 +5043,6 @@ static void unaccount_event(struct perf_event *event) schedule_delayed_work(&perf_sched_work, HZ); } =20 - unaccount_event_cpu(event, event->cpu); - unaccount_pmu_sb_event(event); } =20 @@ -11679,15 +11672,6 @@ static void account_pmu_sb_event(struct perf_event= *event) attach_sb_event(event); } =20 -static void account_event_cpu(struct perf_event *event, int cpu) -{ - if (event->parent) - return; - - if (is_cgroup_event(event)) - atomic_inc(&per_cpu(perf_cgroup_events, cpu)); -} - /* Freq events need the tick to stay alive (see perf_event_task_tick). */ static void account_freq_event_nohz(void) { @@ -11775,8 +11759,6 @@ static void account_event(struct perf_event *event) } enabled: =20 - account_event_cpu(event, event->cpu); - account_pmu_sb_event(event); } =20 @@ -12822,13 +12804,11 @@ static void __perf_pmu_remove(struct perf_event_c= ontext *ctx, =20 perf_event_groups_for_cpu_pmu(event, groups, cpu, pmu) { perf_remove_from_context(event, 0); - unaccount_event_cpu(event, cpu); put_pmu_ctx(event->pmu_ctx); list_add(&event->migrate_entry, events); =20 for_each_sibling_event(sibling, event) { perf_remove_from_context(sibling, 0); - unaccount_event_cpu(sibling, cpu); put_pmu_ctx(sibling->pmu_ctx); list_add(&sibling->migrate_entry, events); } @@ -12847,7 +12827,6 @@ static void __perf_pmu_install_event(struct pmu *pm= u, =20 if (event->state >=3D PERF_EVENT_STATE_OFF) event->state =3D PERF_EVENT_STATE_INACTIVE; - account_event_cpu(event, cpu); perf_install_in_context(ctx, event, cpu); } =20 @@ -13742,8 +13721,7 @@ static int __perf_cgroup_move(void *info) struct task_struct *task =3D info; =20 preempt_disable(); - if (atomic_read(this_cpu_ptr(&perf_cgroup_events))) - perf_cgroup_switch(task); + perf_cgroup_switch(task); preempt_enable(); =20 return 0; --=20 2.37.2