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 03FFBC4332F for ; Wed, 9 Nov 2022 01:20:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229853AbiKIBUX (ORCPT ); Tue, 8 Nov 2022 20:20:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56412 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229498AbiKIBUQ (ORCPT ); Tue, 8 Nov 2022 20:20:16 -0500 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E99A5EF86 for ; Tue, 8 Nov 2022 17:20:15 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id j132-20020a25238a000000b006da635e2073so1937373ybj.2 for ; Tue, 08 Nov 2022 17:20:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=j6fE8FxgLYcEMehZwA0N2DtD/pkodntXjTOaWzFjwNs=; b=G82DxUUKkFjF1wncsDmqTkLHk/sd6bqbbW7zwR50cMvz+RdKCgOeSxk0UULEPJJNlr yMFSXKPE5k0lRGeJ6fqMnnb4rJ+NU4TCxBZp5EG9ZI12XRc/trq3ERWA7PaDo+9OKeOy PFGL2GoKlGQsaUFuJLOzc3SJOsY49x1KRsslIVE4nBisGr9OFBwpn2SVR3y2cdyQf0sS van/mFWpqxXYXMlRbZpW5XE0SdzmxdYZqUhgRSjDNXTE80xPVue+l88ks6IE8eUqCjQY xuGJC8AmyFZeE5+GKBreMsUuXpJorjREReJishdpfBFsIK2RltclZPvJd36HgBZx9bzi h5TA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=j6fE8FxgLYcEMehZwA0N2DtD/pkodntXjTOaWzFjwNs=; b=T9vYdK8CCFCsW6wfW9fi58kgxikZ5QLDsSms099ucyWKam3mFLvKIFisuV/iy2HyQg z+3uERdKp5Ph/uQmaw+UlzHNQPCA+6AFaCT9D+9CRyJejwLyoX8/Mo0oIqVWrPOVP0xm Dyp+D1b6WB3P+Mz6qEVp2ZhTJ2FFSw8qc3aZNa8XjRQxX0VdVe8a3cLg5WCIsDomqXSn r9iWePPFIU24o+bJgAA0sMfhghj9MRIdJz2TdUiC3sRHBTtOfXWvo7WqjaL1/sGh1qh0 dGio/HubftQ9WeuLoAbeXAUSHsnX2l299SV+KAGgKYaHFlqpYuj+eY7tHTkcu+p9EHrO qe/w== X-Gm-Message-State: ACrzQf2Oy+GrMLnaGFohsHdKUhiJR7sDNX/+ifLeoB7+QLbR6oTLsJ3q eSiMtHpLUBwWtIXa2e2qVGzG+brO1pPimg== X-Google-Smtp-Source: AMsMyM72KpCDzxmSblP6ZCKZ9EceK0P0lmfreJqtFk2a010bAeguR4EBWdc+isdNeOitpfoDrDjHc1GCOx1abg== X-Received: from shakeelb.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:262e]) (user=shakeelb job=sendgmr) by 2002:a0d:c486:0:b0:370:2f43:e848 with SMTP id g128-20020a0dc486000000b003702f43e848mr54229772ywd.361.1667956814847; Tue, 08 Nov 2022 17:20:14 -0800 (PST) Date: Wed, 9 Nov 2022 01:20:11 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog Message-ID: <20221109012011.881058-1-shakeelb@google.com> Subject: [PATCH v2] percpu_counter: add percpu_counter_sum_all interface From: Shakeel Butt To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Marek Szyprowski Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The percpu_counter is used for scenarios where performance is more important than the accuracy. For percpu_counter users, who want more accurate information in their slowpath, percpu_counter_sum is provided which traverses all the online CPUs to accumulate the data. The reason it only needs to traverse online CPUs is because percpu_counter does implement CPU offline callback which syncs the local data of the offlined CPU. However there is a small race window between the online CPUs traversal of percpu_counter_sum and the CPU offline callback. The offline callback has to traverse all the percpu_counters on the system to flush the CPU local data which can be a lot. During that time, the CPU which is going offline has already been published as offline to all the readers. So, as the offline callback is running, percpu_counter_sum can be called for one counter which has some state on the CPU going offline. Since percpu_counter_sum only traverses online CPUs, it will skip that specific CPU and the offline callback might not have flushed the state for that specific percpu_counter on that offlined CPU. Normally this is not an issue because percpu_counter users can deal with some inaccuracy for small time window. However a new user i.e. mm_struct on the cleanup path wants to check the exact state of the percpu_counter through check_mm(). For such users, this patch introduces percpu_counter_sum_all() which traverses all possible CPUs and it is used in fork.c:check_mm() to avoid the potential race. Signed-off-by: Shakeel Butt Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski --- Changes since v1: - Only call percpu_counter_sum_all() if percpu_counter_sum() gives non-zero value in check_mm(). include/linux/percpu_counter.h | 6 ++++++ kernel/fork.c | 5 +++++ lib/percpu_counter.c | 29 +++++++++++++++++++++++------ 3 files changed, 34 insertions(+), 6 deletions(-) diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index bde6c4c1f405..a3aae8d57a42 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -45,6 +45,7 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 amount); void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch); s64 __percpu_counter_sum(struct percpu_counter *fbc); +s64 percpu_counter_sum_all(struct percpu_counter *fbc); int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch); void percpu_counter_sync(struct percpu_counter *fbc); @@ -193,6 +194,11 @@ static inline s64 percpu_counter_sum(struct percpu_counter *fbc) return percpu_counter_read(fbc); } +static inline s64 percpu_counter_sum_all(struct percpu_counter *fbc) +{ + return percpu_counter_read(fbc); +} + static inline bool percpu_counter_initialized(struct percpu_counter *fbc) { return true; diff --git a/kernel/fork.c b/kernel/fork.c index 9c32f593ef11..9f7fe3541897 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -758,6 +758,11 @@ static void check_mm(struct mm_struct *mm) for (i = 0; i < NR_MM_COUNTERS; i++) { long x = percpu_counter_sum(&mm->rss_stat[i]); + if (likely(!x)) + continue; + + /* Making sure this is not due to race with CPU offlining. */ + x = percpu_counter_sum_all(&mm->rss_stat[i]); if (unlikely(x)) pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n", mm, resident_page_types[i], x); diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index ed610b75dc32..42f729c8e56c 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -117,11 +117,8 @@ void percpu_counter_sync(struct percpu_counter *fbc) } EXPORT_SYMBOL(percpu_counter_sync); -/* - * Add up all the per-cpu counts, return the result. This is a more accurate - * but much slower version of percpu_counter_read_positive() - */ -s64 __percpu_counter_sum(struct percpu_counter *fbc) +static s64 __percpu_counter_sum_mask(struct percpu_counter *fbc, + const struct cpumask *cpu_mask) { s64 ret; int cpu; @@ -129,15 +126,35 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) raw_spin_lock_irqsave(&fbc->lock, flags); ret = fbc->count; - for_each_online_cpu(cpu) { + for_each_cpu(cpu, cpu_mask) { s32 *pcount = per_cpu_ptr(fbc->counters, cpu); ret += *pcount; } raw_spin_unlock_irqrestore(&fbc->lock, flags); return ret; } + +/* + * Add up all the per-cpu counts, return the result. This is a more accurate + * but much slower version of percpu_counter_read_positive() + */ +s64 __percpu_counter_sum(struct percpu_counter *fbc) +{ + return __percpu_counter_sum_mask(fbc, cpu_online_mask); +} EXPORT_SYMBOL(__percpu_counter_sum); +/* + * This is slower version of percpu_counter_sum as it traverses all possible + * cpus. Use this only in the cases where accurate data is needed in the + * presense of CPUs getting offlined. + */ +s64 percpu_counter_sum_all(struct percpu_counter *fbc) +{ + return __percpu_counter_sum_mask(fbc, cpu_possible_mask); +} +EXPORT_SYMBOL(percpu_counter_sum_all); + int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, struct lock_class_key *key) { -- 2.38.1.431.g37b22c650d-goog