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([2600:380:b444:c00:74e0:9880:f256:e2b6]) by smtp.gmail.com with ESMTPSA id 33-20020a630b21000000b0046ffe3fea77sm13570293pgl.76.2022.12.08.15.00.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Dec 2022 15:00:12 -0800 (PST) Message-ID: Date: Thu, 8 Dec 2022 16:00:10 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH-block 3/3] blk-cgroup: Flush stats at blkgs destruction path Content-Language: en-US To: Waiman Long , 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=c3=bd?= , "Dennis Zhou (Facebook)" References: <20221208220141.2625775-1-longman@redhat.com> <20221208220141.2625775-4-longman@redhat.com> From: Jens Axboe In-Reply-To: <20221208220141.2625775-4-longman@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/8/22 3:01?PM, Waiman Long wrote: > diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c > index 793ecff29038..910e633869b0 100644 > --- a/kernel/cgroup/rstat.c > +++ b/kernel/cgroup/rstat.c > @@ -281,6 +281,26 @@ 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); > + rcu_read_lock(); > + css->ss->css_rstat_flush(css, cpu); > + rcu_read_unlock(); > + raw_spin_unlock_irq(cpu_lock); > +} > + > int cgroup_rstat_init(struct cgroup *cgrp) > { > int cpu; As I mentioned last time, raw_spin_lock_irq() will be equivalent to an RCU protected section anyway, so you don't need to do both. Just add a comment on why rcu_read_lock()/rcu_read_unlock() isn't needed inside the raw irq safe lock. -- Jens Axboe