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bh=h+iH+gyUSP9RmZybF0rRU4rA5/id1U9+eBsl2PUnAPQ=; b=Li7zuSVUekrYZlysizQSX2K/ojAmuTLtWF8FBzUEQPm0tOmJcTGKF1Dt15m1icV5uOrak0 ZSYcilF01D/lKa5Ul19ZqPCyuRymM84xB9Sexcey/bn20g42FAUGHX3e5uIYuAtqpPZ3Iu 5wOHNMl21zU0h/fCSTdB7ZuFjHdtnC0= 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-617-cFUaBO_WOZqWlEoTA3QSDA-1; Tue, 13 Dec 2022 13:45:00 -0500 X-MC-Unique: cFUaBO_WOZqWlEoTA3QSDA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 66E001C008A7; Tue, 13 Dec 2022 18:44:59 +0000 (UTC) Received: from llong.com (unknown [10.22.32.205]) by smtp.corp.redhat.com (Postfix) with ESMTP id A8242C15BA0; Tue, 13 Dec 2022 18:44:58 +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 v3 2/2] blk-cgroup: Flush stats at blkgs destruction path Date: Tue, 13 Dec 2022 13:44:46 -0500 Message-Id: <20221213184446.50181-3-longman@redhat.com> In-Reply-To: <20221213184446.50181-1-longman@redhat.com> References: <20221213184446.50181-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Rspam-User: X-Rspamd-Queue-Id: 433D01A0018 X-Rspamd-Server: rspam01 X-Stat-Signature: epp39utpji4rxb9dec4cyiuf8n34tmbp X-HE-Tag: 1670957104-131857 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 | 15 +++++++++++++++ include/linux/cgroup.h | 1 + kernel/cgroup/rstat.c | 18 ++++++++++++++++++ 3 files changed, 34 insertions(+) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index ca28306aa1b1..ddd27a714d3e 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1084,6 +1084,8 @@ 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. @@ -1093,6 +1095,19 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) might_sleep(); + /* + * Flush all the non-empty percpu lockless lists so as to release + * the blkg references held by those lists which, in turn, may + * allow the blkgs to be freed and release their references to + * blkcg speeding up its freeing. + */ + 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;