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 C0FDFC77B73 for ; Wed, 24 May 2023 04:20:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238604AbjEXEUq (ORCPT ); Wed, 24 May 2023 00:20:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235814AbjEXEUk (ORCPT ); Wed, 24 May 2023 00:20:40 -0400 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 91D1DC1 for ; Tue, 23 May 2023 21:20:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684902001; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nNL45LO8EXEJZUqjzGz/C9lTP9F5PHqVMSM+e2igsc8=; b=CzPykviUhiZA2IUMj2l1+8kPtj/tE+v1ycG9b/spPnm6O7rxIjpveWj6tnpsLuonxfU14I Gbf/147LLbiJs18NIH9xNcw/I+coKcHckNIKLL27nUTcuZ5JXwGmGvzyog67mMJ1m3S819 1Pox491W/O+kzOv6cxT/1Deehqy9avk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-451-ZMNAg8RwOZ-UIcQNG88NGA-1; Wed, 24 May 2023 00:19:58 -0400 X-MC-Unique: ZMNAg8RwOZ-UIcQNG88NGA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E69F6185A78F; Wed, 24 May 2023 04:19:57 +0000 (UTC) Received: from [10.22.8.64] (unknown [10.22.8.64]) by smtp.corp.redhat.com (Postfix) with ESMTP id 90F8C9D73; Wed, 24 May 2023 04:19:57 +0000 (UTC) Message-ID: Date: Wed, 24 May 2023 00:19:57 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH V2] blk-cgroup: Flush stats before releasing blkcg_gq Content-Language: en-US To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, Tejun Heo , mkoutny@suse.com, Yosry Ahmed References: <20230524035150.727407-1-ming.lei@redhat.com> From: Waiman Long In-Reply-To: <20230524035150.727407-1-ming.lei@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 5/23/23 23:51, Ming Lei wrote: > 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 and some blkgs from being freed after > they are made offline. > > It is less a problem if the cgroup to be destroyed also has other > controllers like memory that will call cgroup_rstat_flush() which will > clean up the reference count. If block is the only controller that uses > rstat, these offline blkcg and blkgs may never be freed leaking more > and more memory over time. > > To prevent this potential memory leak: > > - flush blkcg per-cpu stats list in __blkg_release(), when no new stat > can be added > > - don't grab bio->bi_blkg reference when adding the stats into blkcg's > per-cpu stat list since all stats are guaranteed to be consumed before > releasing blkg instance, and grabbing blkg reference for stats was the > most fragile part of original patch > > Based on Waiman's patch: > > https://lore.kernel.org/linux-block/20221215033132.230023-3-longman@redhat.com/ > > Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") > Cc: Waiman Long > Cc: Tejun Heo > Cc: mkoutny@suse.com > Cc: Yosry Ahmed > Signed-off-by: Ming Lei > --- > V2: > - remove kernel/cgroup change, and call blkcg_rstat_flush() > to flush stat directly > > block/blk-cgroup.c | 29 +++++++++++++++++++++-------- > 1 file changed, 21 insertions(+), 8 deletions(-) > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index 0ce64dd73cfe..ed0eb8896972 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -34,6 +34,8 @@ > #include "blk-ioprio.h" > #include "blk-throttle.h" > > +static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu); > + > /* > * blkcg_pol_mutex protects blkcg_policy[] and policy [de]activation. > * blkcg_pol_register_mutex nests outside of it and synchronizes entire > @@ -163,10 +165,21 @@ static void blkg_free(struct blkcg_gq *blkg) > static void __blkg_release(struct rcu_head *rcu) > { > struct blkcg_gq *blkg = container_of(rcu, struct blkcg_gq, rcu_head); > + struct blkcg *blkcg = blkg->blkcg; > + int cpu; > > #ifdef CONFIG_BLK_CGROUP_PUNT_BIO > WARN_ON(!bio_list_empty(&blkg->async_bios)); > #endif > + /* > + * Flush all the non-empty percpu lockless lists before releasing > + * us, given these stat belongs to us. > + * > + * cgroup locks aren't needed here since __blkcg_rstat_flush just > + * propagates delta into blkg parent, which is live now. > + */ > + for_each_possible_cpu(cpu) > + __blkcg_rstat_flush(blkcg, cpu); > > /* release the blkcg and parent blkg refs this blkg has been holding */ > css_put(&blkg->blkcg->css); > @@ -951,17 +964,12 @@ static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur, > u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags); > } > > -static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu) > +static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) > { > - struct blkcg *blkcg = css_to_blkcg(css); > struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu); > struct llist_node *lnode; > struct blkg_iostat_set *bisc, *next_bisc; > > - /* Root-level stats are sourced from system-wide IO stats */ > - if (!cgroup_parent(css->cgroup)) > - return; > - > rcu_read_lock(); > > lnode = llist_del_all(lhead); > @@ -991,13 +999,19 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu) > if (parent && parent->parent) > blkcg_iostat_update(parent, &blkg->iostat.cur, > &blkg->iostat.last); > - percpu_ref_put(&blkg->refcnt); > } > > out: > rcu_read_unlock(); > } > > +static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu) > +{ > + /* Root-level stats are sourced from system-wide IO stats */ > + if (cgroup_parent(css->cgroup)) > + __blkcg_rstat_flush(css_to_blkcg(css), cpu); > +} > + I think it may not safe to call __blkcg_rstat_flus() directly without taking the cgroup_rstat_cpu_lock. That is why I added a helper to kernel/cgroup/rstat.c in my patch to meet the locking requirement. Cheers, Longman