Re: [PATCH-block 3/3] blk-cgroup: Flush stats at blkgs destruction path

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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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