From patchwork Sun Dec 11 22:20:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13070675 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 C2D31C001B2 for ; Sun, 11 Dec 2022 22:22:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230367AbiLKWWI (ORCPT ); Sun, 11 Dec 2022 17:22:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229625AbiLKWWH (ORCPT ); Sun, 11 Dec 2022 17:22:07 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B3BFCE0 for ; Sun, 11 Dec 2022 14:21:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1670797272; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=k/HK6fMXdxgz4kcaH4vQrOdm/WfD552GcWScyCwHZ9A=; b=gv8yrf9u1UUylYtNCcp520HPRybEBEBjcyvXVSwx8qstgQeXB2DDF24QAWRAWjxHv6dyEu YAk3OZW1zIeHoyAjT3AZ0wq74NfD1xRCnUHSAbKPlxMt1Su2efj/NP9fX0wKzsbuAxKdlc UwAbrMKdMnxt9O7PrMDnk4CQuHQuZEo= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-567-gXbDyWjHO-mp8qogjpDY2A-1; Sun, 11 Dec 2022 17:21:09 -0500 X-MC-Unique: gXbDyWjHO-mp8qogjpDY2A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B196D3C01D8F; Sun, 11 Dec 2022 22:21:08 +0000 (UTC) Received: from llong.com (unknown [10.22.16.68]) by smtp.corp.redhat.com (Postfix) with ESMTP id 37C721121331; Sun, 11 Dec 2022 22:21:08 +0000 (UTC) From: Waiman Long To: Jens Axboe , Tejun Heo , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?utf-8?q?Michal_Koutn?= =?utf-8?q?=C3=BD?= , "Dennis Zhou (Facebook)" , Waiman Long Subject: [PATCH-block v2 3/3] blk-cgroup: Flush stats at blkgs destruction path Date: Sun, 11 Dec 2022 17:20:58 -0500 Message-Id: <20221211222058.2946830-4-longman@redhat.com> In-Reply-To: <20221211222058.2946830-1-longman@redhat.com> References: <20221211222058.2946830-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org As noted by Michal, the blkg_iostat_set's in the lockless list hold reference to blkg's to protect against their removal. Those blkg's hold reference to blkcg. When a cgroup is being destroyed, cgroup_rstat_flush() is only called at css_release_work_fn() which is called when the blkcg reference count reaches 0. This circular dependency will prevent blkcg from being freed until some other events cause cgroup_rstat_flush() to be called to flush out the pending blkcg stats. To prevent this delayed blkcg removal, add a new cgroup_rstat_css_flush() function to flush stats for a given css and cpu and call it at the blkgs destruction path, blkcg_destroy_blkgs(), whenever there are still some pending stats to be flushed. This will ensure that blkcg reference count can reach 0 ASAP. Signed-off-by: Waiman Long Acked-by: Tejun Heo --- block/blk-cgroup.c | 12 ++++++++++++ include/linux/cgroup.h | 1 + kernel/cgroup/rstat.c | 18 ++++++++++++++++++ 3 files changed, 31 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index c466aef0d467..534f3baeb84a 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1090,6 +1090,8 @@ struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css) */ static void blkcg_destroy_blkgs(struct blkcg *blkcg) { + int cpu; + /* * blkcg_destroy_blkgs() shouldn't be called with all the blkcg * references gone. @@ -1099,6 +1101,16 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) might_sleep(); + /* + * Flush all the non-empty percpu lockless lists. + */ + for_each_possible_cpu(cpu) { + struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu); + + if (!llist_empty(lhead)) + cgroup_rstat_css_cpu_flush(&blkcg->css, cpu); + } + spin_lock_irq(&blkcg->lock); while (!hlist_empty(&blkcg->blkg_list)) { diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 528bd44b59e2..6c4e66b3fa84 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -766,6 +766,7 @@ void cgroup_rstat_flush(struct cgroup *cgrp); void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp); void cgroup_rstat_flush_hold(struct cgroup *cgrp); void cgroup_rstat_flush_release(void); +void cgroup_rstat_css_cpu_flush(struct cgroup_subsys_state *css, int cpu); /* * Basic resource stats. diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 793ecff29038..2e44be44351f 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -281,6 +281,24 @@ void cgroup_rstat_flush_release(void) spin_unlock_irq(&cgroup_rstat_lock); } +/** + * cgroup_rstat_css_cpu_flush - flush stats for the given css and cpu + * @css: target css to be flush + * @cpu: the cpu that holds the stats to be flush + * + * A lightweight rstat flush operation for a given css and cpu. + * Only the cpu_lock is being held for mutual exclusion, the cgroup_rstat_lock + * isn't used. + */ +void cgroup_rstat_css_cpu_flush(struct cgroup_subsys_state *css, int cpu) +{ + raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu); + + raw_spin_lock_irq(cpu_lock); + css->ss->css_rstat_flush(css, cpu); + raw_spin_unlock_irq(cpu_lock); +} + int cgroup_rstat_init(struct cgroup *cgrp) { int cpu;