Commit e7b20d97 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: Restructure release_agent_path handling 



cgrp->root->release_agent_path is protected by both cgroup_mutex and
release_agent_path_lock and readers can hold either one. The
dual-locking scheme was introduced while breaking a locking dependency
issue around cgroup_mutex but doesn't make sense anymore given that
the only remaining reader which uses cgroup_mutex is
cgroup1_releaes_agent().

This patch updates cgroup1_release_agent() to use
release_agent_path_lock so that release_agent_path is always protected
only by release_agent_path_lock.

While at it, convert strlen() based empty string checks to direct
tests on the first character as suggested by Linus.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
parent a09833f7

kernel/cgroup/cgroup-v1.c

+17 −17
Original line number Diff line number Diff line
@@ -38,10 +38,7 @@ static bool cgroup_no_v1_named; 
 */

static struct workqueue_struct *cgroup_pidlist_destroy_wq;



/*

 * Protects cgroup_subsys->release_agent_path.  Modifying it also requires

 * cgroup_mutex.  Reading requires either cgroup_mutex or this spinlock.

 */

/* protects cgroup_subsys->release_agent_path */

static DEFINE_SPINLOCK(release_agent_path_lock);



bool cgroup1_ssid_disabled(int ssid)
@@ -775,22 +772,29 @@ void cgroup1_release_agent(struct work_struct *work) 
{

	struct cgroup *cgrp =

		container_of(work, struct cgroup, release_agent_work);

	char *pathbuf = NULL, *agentbuf = NULL;

	char *pathbuf, *agentbuf;

	char *argv[3], *envp[3];

	int ret;



	mutex_lock(&cgroup_mutex);

	/* snoop agent path and exit early if empty */

	if (!cgrp->root->release_agent_path[0])

		return;



	/* prepare argument buffers */

	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);

	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);

	if (!pathbuf || !agentbuf || !strlen(agentbuf))

		goto out;

	agentbuf = kmalloc(PATH_MAX, GFP_KERNEL);

	if (!pathbuf || !agentbuf)

		goto out_free;



	spin_lock_irq(&css_set_lock);

	ret = cgroup_path_ns_locked(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);

	spin_unlock_irq(&css_set_lock);

	spin_lock(&release_agent_path_lock);

	strlcpy(agentbuf, cgrp->root->release_agent_path, PATH_MAX);

	spin_unlock(&release_agent_path_lock);

	if (!agentbuf[0])

		goto out_free;



	ret = cgroup_path_ns(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns);

	if (ret < 0 || ret >= PATH_MAX)

		goto out;

		goto out_free;



	argv[0] = agentbuf;

	argv[1] = pathbuf;
@@ -801,11 +805,7 @@ void cgroup1_release_agent(struct work_struct *work) 
	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";

	envp[2] = NULL;



	mutex_unlock(&cgroup_mutex);

	call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);

	goto out_free;

out:

	mutex_unlock(&cgroup_mutex);

out_free:

	kfree(agentbuf);

	kfree(pathbuf);

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