Commit 3ee4211e authored by pengdonglin's avatar pengdonglin Committed by Tejun Heo
Browse files

cgroup: Remove redundant rcu_read_lock/unlock() in spin_lock 



Since commit a8bb74ac ("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: default avatarpengdonglin <pengdonglin@xiaomi.com>
Signed-off-by: default avatarpengdonglin <dolinux.peng@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 0568f89d

kernel/cgroup/cgroup.c

+0 −2
Original line number Diff line number Diff line
@@ -3025,14 +3025,12 @@ 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 */

kernel/cgroup/debug.c

+0 −4
Original line number Diff line number Diff line
@@ -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;