From patchwork Wed Jul 7 01:56:49 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yu Kuai X-Patchwork-Id: 12361407 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 96C09C07E96 for ; Wed, 7 Jul 2021 01:48:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D19C61CB6 for ; Wed, 7 Jul 2021 01:48:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229993AbhGGBvF (ORCPT ); Tue, 6 Jul 2021 21:51:05 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:6433 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229949AbhGGBvF (ORCPT ); Tue, 6 Jul 2021 21:51:05 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GKMgD5pGQz76qf; Wed, 7 Jul 2021 09:44:56 +0800 (CST) Received: from dggema762-chm.china.huawei.com (10.1.198.204) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Wed, 7 Jul 2021 09:48:23 +0800 Received: from huawei.com (10.175.127.227) by dggema762-chm.china.huawei.com (10.1.198.204) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Wed, 7 Jul 2021 09:48:23 +0800 From: Yu Kuai To: , CC: , , , , Subject: [PATCH V2] blk-cgroup: prevent rcu_sched detected stalls warnings while iterating blkgs Date: Wed, 7 Jul 2021 09:56:49 +0800 Message-ID: <20210707015649.1929797-1-yukuai3@huawei.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Originating-IP: [10.175.127.227] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggema762-chm.china.huawei.com (10.1.198.204) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org We run a test that create millions of cgroups and blkgs, and then trigger blkg_destroy_all(). blkg_destroy_all() will hold spin lock for a long time in such situation. Thus release the lock when a batch of blkgs are destroyed. blkcg_activate_policy() and blkcg_deactivate_policy() might have the same problem, however, as they are basically only called from module init/exit paths, let's leave them alone for now. Signed-off-by: Yu Kuai Acked-by: Tejun Heo --- changes in V2: - as suggested by Tejun, rename 'BLKG_DESTROY_BATCH_SIZE' and modify blkg_destroy_all() only. block/blk-cgroup.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 7b06a5fa3cac..575d7a2e7203 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -56,6 +56,8 @@ static LIST_HEAD(all_blkcgs); /* protected by blkcg_pol_mutex */ bool blkcg_debug_stats = false; static struct workqueue_struct *blkcg_punt_bio_wq; +#define BLKG_DESTROY_BATCH_SIZE 64 + static bool blkcg_policy_enabled(struct request_queue *q, const struct blkcg_policy *pol) { @@ -422,7 +424,9 @@ static void blkg_destroy(struct blkcg_gq *blkg) static void blkg_destroy_all(struct request_queue *q) { struct blkcg_gq *blkg, *n; + int count = BLKG_DESTROY_BATCH_SIZE; +restart: spin_lock_irq(&q->queue_lock); list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) { struct blkcg *blkcg = blkg->blkcg; @@ -430,6 +434,17 @@ static void blkg_destroy_all(struct request_queue *q) spin_lock(&blkcg->lock); blkg_destroy(blkg); spin_unlock(&blkcg->lock); + + /* + * in order to avoid holding the spin lock for too long, release + * it when a batch of blkgs are destroyed. + */ + if (!(--count)) { + count = BLKG_DESTROY_BATCH_SIZE; + spin_unlock_irq(&q->queue_lock); + cond_resched(); + goto restart; + } } q->root_blkg = NULL;