[PATCH v3 08/14] cgroup: Remove redundant rcu_read_lock/unlock() in spin_lock

[pengdonglin <dolinux.peng@gmail.com>]

From: pengdonglin <pengdonglin@xiaomi.com>

Since commit a8bb74acd8efe ("rcu: Consolidate RCU-sched update-side function definitions")
there is no difference between rcu_read_lock(), rcu_read_lock_bh() and
rcu_read_lock_sched() in terms of RCU read section and the relevant grace
period. That means that spin_lock(), which implies rcu_read_lock_sched(),
also implies rcu_read_lock().

There is no need no explicitly start a RCU read section if one has already
been started implicitly by spin_lock().

Simplify the code and remove the inner rcu_read_lock() invocation.

Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
Signed-off-by: pengdonglin <dolinux.peng@gmail.com>
---
 kernel/cgroup/cgroup.c | 2 --
 kernel/cgroup/debug.c  | 4 ----
 2 files changed, 6 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 312c6a8b55bb..db9e00a559df 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2944,14 +2944,12 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,
 
 	/* look up all src csets */
 	spin_lock_irq(&css_set_lock);
-	rcu_read_lock();
 	task = leader;
 	do {
 		cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &mgctx);
 		if (!threadgroup)
 			break;
 	} while_each_thread(leader, task);
-	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
 
 	/* prepare dst csets and commit */
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 80aa3f027ac3..81ea38dd6f9d 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -49,7 +49,6 @@ static int current_css_set_read(struct seq_file *seq, void *v)
 		return -ENODEV;
 
 	spin_lock_irq(&css_set_lock);
-	rcu_read_lock();
 	cset = task_css_set(current);
 	refcnt = refcount_read(&cset->refcount);
 	seq_printf(seq, "css_set %pK %d", cset, refcnt);
@@ -67,7 +66,6 @@ static int current_css_set_read(struct seq_file *seq, void *v)
 		seq_printf(seq, "%2d: %-4s\t- %p[%d]\n", ss->id, ss->name,
 			  css, css->id);
 	}
-	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
 	cgroup_kn_unlock(of->kn);
 	return 0;
@@ -95,7 +93,6 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
 		return -ENOMEM;
 
 	spin_lock_irq(&css_set_lock);
-	rcu_read_lock();
 	cset = task_css_set(current);
 	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
 		struct cgroup *c = link->cgrp;
@@ -104,7 +101,6 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
 		seq_printf(seq, "Root %d group %s\n",
 			   c->root->hierarchy_id, name_buf);
 	}
-	rcu_read_unlock();
 	spin_unlock_irq(&css_set_lock);
 	kfree(name_buf);
 	return 0;
-- 
2.34.1