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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=20Koutn=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 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4341E40006 X-Stat-Signature: 8bnprymkxdqbyzigr5wao6f3hjb65r7a X-Rspam-User: X-HE-Tag: 1670797275-238024 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 --- 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; -- 2.31.1