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Commit 69e943b7 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: update locking in cgroup_show_options() 



cgroup_show_options() grabs cgroup_root_mutex to protect the options
changing while printing; however, holding root_mutex or not doesn't
really make much difference for the function.  subsys_mask can be
atomically tested and most of the options aren't allowed to change
anyway once mounted.

The only field which needs synchronization is ->release_agent_path.
This patch introduces a dedicated spinlock to synchronize accesses to
the field and drops cgroup_root_mutex locking from
cgroup_show_options().  The next patch will remove cgroup_root_mutex.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent aec25020

kernel/cgroup.c

+16 −3
Original line number Original line Diff line number Diff line
@@ -92,6 +92,12 @@ static DEFINE_MUTEX(cgroup_mutex); 




static DEFINE_MUTEX(cgroup_root_mutex);

static DEFINE_MUTEX(cgroup_root_mutex);





/*

 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires

 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.

 */

static DEFINE_SPINLOCK(release_agent_path_lock);



#define cgroup_assert_mutex_or_rcu_locked()				\

#define cgroup_assert_mutex_or_rcu_locked()				\

	rcu_lockdep_assert(rcu_read_lock_held() ||			\

	rcu_lockdep_assert(rcu_read_lock_held() ||			\

			   lockdep_is_held(&cgroup_mutex),		\

			   lockdep_is_held(&cgroup_mutex),		\
@@ -1034,7 +1040,6 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry) 
	struct cgroup_subsys *ss;

	struct cgroup_subsys *ss;

	int ssid;

	int ssid;





	mutex_lock(&cgroup_root_mutex);

	for_each_subsys(ss, ssid)

	for_each_subsys(ss, ssid)

		if (root->subsys_mask & (1 << ssid))

		if (root->subsys_mask & (1 << ssid))

			seq_printf(seq, ",%s", ss->name);

			seq_printf(seq, ",%s", ss->name);
@@ -1044,13 +1049,16 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry) 
		seq_puts(seq, ",noprefix");

		seq_puts(seq, ",noprefix");

	if (root->flags & CGRP_ROOT_XATTR)

	if (root->flags & CGRP_ROOT_XATTR)

		seq_puts(seq, ",xattr");

		seq_puts(seq, ",xattr");



	spin_lock(&release_agent_path_lock);

	if (strlen(root->release_agent_path))

	if (strlen(root->release_agent_path))

		seq_printf(seq, ",release_agent=%s", root->release_agent_path);

		seq_printf(seq, ",release_agent=%s", root->release_agent_path);

	spin_unlock(&release_agent_path_lock);



	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))

	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))

		seq_puts(seq, ",clone_children");

		seq_puts(seq, ",clone_children");

	if (strlen(root->name))

	if (strlen(root->name))

		seq_printf(seq, ",name=%s", root->name);

		seq_printf(seq, ",name=%s", root->name);

	mutex_unlock(&cgroup_root_mutex);

	return 0;

	return 0;

}

}
@@ -1272,8 +1280,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data) 
	if (ret)

	if (ret)

		goto out_unlock;

		goto out_unlock;





	if (opts.release_agent)

	if (opts.release_agent) {

		spin_lock(&release_agent_path_lock);

		strcpy(root->release_agent_path, opts.release_agent);

		strcpy(root->release_agent_path, opts.release_agent);

		spin_unlock(&release_agent_path_lock);

	}

 out_unlock:

 out_unlock:

	kfree(opts.release_agent);

	kfree(opts.release_agent);

	kfree(opts.name);

	kfree(opts.name);
@@ -2183,7 +2194,9 @@ static int cgroup_release_agent_write(struct cgroup_subsys_state *css, 
	if (!cgroup_lock_live_group(css->cgroup))

	if (!cgroup_lock_live_group(css->cgroup))

		return -ENODEV;

		return -ENODEV;

	mutex_lock(&cgroup_root_mutex);

	mutex_lock(&cgroup_root_mutex);

	spin_lock(&release_agent_path_lock);

	strcpy(css->cgroup->root->release_agent_path, buffer);

	strcpy(css->cgroup->root->release_agent_path, buffer);

	spin_unlock(&release_agent_path_lock);

	mutex_unlock(&cgroup_root_mutex);

	mutex_unlock(&cgroup_root_mutex);

	mutex_unlock(&cgroup_mutex);

	mutex_unlock(&cgroup_mutex);

	return 0;

	return 0;