cgroup: Factor out and expose cgroup_rstat_*() interface functions

cgroup_rstat is being generalized so that controllers can use it too.
This patch factors out and exposes the following interface functions.

* cgroup_rstat_updated(): Renamed from cgroup_rstat_cpu_updated() for
  consistency.

* cgroup_rstat_flush_hold/release(): Factored out from base stat
  implementation.

* cgroup_rstat_flush(): Verbatim expose.

While at it, drop assert on cgroup_rstat_mutex in
cgroup_base_stat_flush() as it crosses layers and make a minor comment
update.

v2: Added EXPORT_SYMBOL_GPL(cgroup_rstat_updated) to fix a build bug.

Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 30 insertions, 13 deletions

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 2bf6fb417588..b68e1a7c146c 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -203,7 +203,6 @@ int cgroup_task_count(const struct cgroup *cgrp);
 /*
  * rstat.c
  */
-void cgroup_rstat_flush(struct cgroup *cgrp);
 int cgroup_rstat_init(struct cgroup *cgrp);
 void cgroup_rstat_exit(struct cgroup *cgrp);
 void cgroup_rstat_boot(void);
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 87d7252769e7..d49bf92ac3d4 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -13,7 +13,7 @@ static struct cgroup_rstat_cpu *cgroup_rstat_cpu(struct cgroup *cgrp, int cpu)
 }
 
 /**
- * cgroup_rstat_cpu_updated - keep track of updated rstat_cpu
+ * cgroup_rstat_updated - keep track of updated rstat_cpu
  * @cgrp: target cgroup
  * @cpu: cpu on which rstat_cpu was updated
  *
@@ -21,7 +21,7 @@ static struct cgroup_rstat_cpu *cgroup_rstat_cpu(struct cgroup *cgrp, int cpu)
  * rstat_cpu->updated_children list.  See the comment on top of
  * cgroup_rstat_cpu definition for details.
  */
-static void cgroup_rstat_cpu_updated(struct cgroup *cgrp, int cpu)
+void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
 {
         raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
         struct cgroup *parent;
@@ -59,6 +59,7 @@ static void cgroup_rstat_cpu_updated(struct cgroup *cgrp, int cpu)
 
         raw_spin_unlock_irqrestore(cpu_lock, flags);
 }
+EXPORT_SYMBOL_GPL(cgroup_rstat_updated);
 
 /**
  * cgroup_rstat_cpu_pop_updated - iterate and dismantle rstat_cpu updated tree
@@ -167,6 +168,29 @@ void cgroup_rstat_flush(struct cgroup *cgrp)
         mutex_unlock(&cgroup_rstat_mutex);
 }
 
+/**
+ * cgroup_rstat_flush_begin - flush stats in @cgrp's subtree and hold
+ * @cgrp: target cgroup
+ *
+ * Flush stats in @cgrp's subtree and prevent further flushes.  Must be
+ * paired with cgroup_rstat_flush_release().
+ */
+void cgroup_rstat_flush_hold(struct cgroup *cgrp)
+        __acquires(&cgroup_rstat_mutex)
+{
+        mutex_lock(&cgroup_rstat_mutex);
+        cgroup_rstat_flush_locked(cgrp);
+}
+
+/**
+ * cgroup_rstat_flush_release - release cgroup_rstat_flush_hold()
+ */
+void cgroup_rstat_flush_release(void)
+        __releases(&cgroup_rstat_mutex)
+{
+        mutex_unlock(&cgroup_rstat_mutex);
+}
+
 int cgroup_rstat_init(struct cgroup *cgrp)
 {
         int cpu;
@@ -239,15 +263,13 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
         struct cgroup_base_stat delta;
         unsigned seq;
 
-        lockdep_assert_held(&cgroup_rstat_mutex);
-
         /* fetch the current per-cpu values */
         do {
                 seq = __u64_stats_fetch_begin(&rstatc->bsync);
                 cputime = rstatc->bstat.cputime;
         } while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
 
-        /* accumulate the deltas to propgate */
+        /* calculate the delta to propgate */
         delta.cputime.utime = cputime.utime - last_cputime->utime;
         delta.cputime.stime = cputime.stime - last_cputime->stime;
         delta.cputime.sum_exec_runtime = cputime.sum_exec_runtime -
@@ -278,7 +300,7 @@ static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
                                                  struct cgroup_rstat_cpu *rstatc)
 {
         u64_stats_update_end(&rstatc->bsync);
-        cgroup_rstat_cpu_updated(cgrp, smp_processor_id());
+        cgroup_rstat_updated(cgrp, smp_processor_id());
         put_cpu_ptr(rstatc);
 }
 
@@ -323,14 +345,10 @@ void cgroup_base_stat_cputime_show(struct seq_file *seq)
         if (!cgroup_parent(cgrp))
                 return;
 
-        mutex_lock(&cgroup_rstat_mutex);
-
-        cgroup_rstat_flush_locked(cgrp);
-
+        cgroup_rstat_flush_hold(cgrp);
         usage = cgrp->bstat.cputime.sum_exec_runtime;
         cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime, &utime, &stime);
-
-        mutex_unlock(&cgroup_rstat_mutex);
+        cgroup_rstat_flush_release();
 
         do_div(usage, NSEC_PER_USEC);
         do_div(utime, NSEC_PER_USEC);