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Date: Fri, 9 Dec 2022 10:58:32 -0500 From: Waiman Long <longman@...hat.com> To: Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>, Zefan Li <lizefan.x@...edance.com>, Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org> Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, Michal Koutný <mkoutny@...e.com>, "Dennis Zhou (Facebook)" <dennisszhou@...il.com> Subject: Re: [PATCH-block 3/3] blk-cgroup: Flush stats at blkgs destruction path On 12/8/22 18:00, Jens Axboe wrote: > 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. Yes, you are right. We don't need rcu_read_lock() here. I put it there to follow the locking pattern in cgroup_rstat_flush_locked(). I will remove it in the next version. Cheers, Longman
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