leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

cgroup: Restructure release_agent_path handling

Browse Source 
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: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2020-03-12 16:44:35 -04:00
parent a09833f7cd
commit e7b20d9796
1 changed files with 17 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
kernel/cgroup/cgroup-v1.c
View File

@ -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);