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Thu, 02 Feb 2023 14:35:10 -0800 (PST) Received: from localhost ([2620:10d:c090:400::5:48a9]) by smtp.gmail.com with ESMTPSA id f5-20020a170902684500b00192820d00d0sm176309pln.120.2023.02.02.14.35.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 14:35:10 -0800 (PST) Date: Thu, 2 Feb 2023 12:35:08 -1000 From: Tejun Heo To: Ming Lei Cc: Waiman Long , Jens Axboe , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal =?iso-8859-1?Q?Koutn=FD?= , "Dennis Zhou (Facebook)" Subject: Re: [PATCH v4 2/2] blk-cgroup: Flush stats at blkgs destruction path Message-ID: References: <20221215033132.230023-1-longman@redhat.com> <20221215033132.230023-3-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: i4i53aidrxk6cwzcsu686z6xmp14d3bg X-Rspamd-Queue-Id: D7AA418001D X-HE-Tag: 1675377311-480829 X-HE-Meta: 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 xGKCQJmq 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Feb 02, 2023 at 12:15:52PM +0800, Ming Lei wrote: > > @@ -1093,6 +1095,20 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) > > > > might_sleep(); > > > > + /* > > + * Flush all the non-empty percpu lockless lists to release the > > + * blkg references held by those lists which, in turn, will > > + * allow those blkgs to be freed and release their references to > > + * blkcg. Otherwise, they may not be freed at all becase of this > > + * circular dependency resulting in memory leak. > > + */ > > + 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); > > + } > > I guess it is possible for new iostat_cpu to be added just after the > llist_empty() check. Ah, good point. Maybe: * Move flush below the blkg kill loop. * In blk_cgroup_bio_start(), use percpu_ref_tryget() to decide whether to add to llist or not. -- tejun