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Commit e76ecaee authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: use cgroup_kn_lock_live() in other cgroup kernfs methods 



Make __cgroup_procs_write() and cgroup_release_agent_write() use
cgroup_kn_lock_live() and cgroup_kn_unlock() instead of
cgroup_lock_live_group().  This puts the operations under both
cgroup_tree_mutex and cgroup_mutex protection without circular
dependency from kernfs active protection.  Also, this means that
cgroup_mutex is no longer nested below kernfs active protection.
There is no longer any place where the two locks interact.

This leaves cgroup_lock_live_group() without any user.  Removed.

This will help simplifying cgroup locking.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent a9746d8d

kernel/cgroup.c

+12 −27
Original line number Diff line number Diff line
@@ -386,23 +386,6 @@ static int notify_on_release(const struct cgroup *cgrp) 
			;						\

		else



/**

 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.

 * @cgrp: the cgroup to be checked for liveness

 *

 * On success, returns true; the mutex should be later unlocked.  On

 * failure returns false with no lock held.

 */

static bool cgroup_lock_live_group(struct cgroup *cgrp)

{

	mutex_lock(&cgroup_mutex);

	if (cgroup_is_dead(cgrp)) {

		mutex_unlock(&cgroup_mutex);

		return false;

	}

	return true;

}



/* the list of cgroups eligible for automatic release. Protected by

 * release_list_lock */

static LIST_HEAD(release_list);
@@ -2306,14 +2289,15 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, 
{

	struct task_struct *tsk;

	const struct cred *cred = current_cred(), *tcred;

	struct cgroup *cgrp = of_css(of)->cgroup;

	struct cgroup *cgrp;

	pid_t pid;

	int ret;



	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)

		return -EINVAL;



	if (!cgroup_lock_live_group(cgrp))

	cgrp = cgroup_kn_lock_live(of->kn);

	if (!cgrp)

		return -ENODEV;



retry_find_task:
@@ -2379,7 +2363,7 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf, 


	put_task_struct(tsk);

out_unlock_cgroup:

	mutex_unlock(&cgroup_mutex);

	cgroup_kn_unlock(of->kn);

	return ret ?: nbytes;

}
@@ -2429,17 +2413,18 @@ static ssize_t cgroup_procs_write(struct kernfs_open_file *of, 
static ssize_t cgroup_release_agent_write(struct kernfs_open_file *of,

					  char *buf, size_t nbytes, loff_t off)

{

	struct cgroup *cgrp = of_css(of)->cgroup;

	struct cgroup_root *root = cgrp->root;

	struct cgroup *cgrp;



	BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX);

	if (!cgroup_lock_live_group(cgrp))

	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);



	cgrp = cgroup_kn_lock_live(of->kn);

	if (!cgrp)

		return -ENODEV;

	spin_lock(&release_agent_path_lock);

	strlcpy(root->release_agent_path, strstrip(buf),

		sizeof(root->release_agent_path));

	strlcpy(cgrp->root->release_agent_path, strstrip(buf),

		sizeof(cgrp->root->release_agent_path));

	spin_unlock(&release_agent_path_lock);

	mutex_unlock(&cgroup_mutex);

	cgroup_kn_unlock(of->kn);

	return nbytes;

}