From mboxrd@z Thu Jan 1 00:00:00 1970 From: 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> References: <20221211222058.2946830-1-longman@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: 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= In-Reply-To: <20221211222058.2946830-1-longman@redhat.com> List-ID: Content-Type: text/plain; charset="us-ascii" 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 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