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authorTejun Heo <tj@kernel.org>2020-03-12 16:44:35 -0400
committerTejun Heo <tj@kernel.org>2020-03-12 16:44:35 -0400
commite7b20d97967c2995700041f0348ea33047e5c942 (patch)
tree00f5a4ddabf212cf94519f9241c4c35cfcd8c5ca /kernel/cgroup
parenta09833f7cdf45b9e85b975646287526fe352d08f (diff)
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: Tejun Heo <tj@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cgroup')
-rw-r--r--kernel/cgroup/cgroup-v1.c34
1 files changed, 17 insertions, 17 deletions
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index f2d7cea86ffe..191c329e482a 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -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);