On 2013/10/14 16:06, Markus Blank-Burian wrote:
> The crash utility indicated, that the lock was held by a kworker
> thread, which was idle at the moment. So there might be a case, where
> no unlock is done. I am trying to reproduce the problem at the moment
> with CONFIG_PROVE_LOCKING, but without luck so far. It seems, that my
> test-job is quite bad at reproducing the bug. I'll let you know, if I
> can find out more.
>
Another way to find out who has been holding cgroup_mutex.
Do a s/mutex_lock(&cgroup_mutex)/cgroup_lock()/g in kernel/cgroup.c,
and add debug printks in cgroup_lock.
When the deadlock happens, the last dump_stack() shows the code path
to cgroup_lock() which leads to deadlock. We won't see idle this way.
=====
based on v3.11.3
--- kernel/cgroup.c.old 2013-10-15 11:21:10.000000000 +0800
+++ kernel/cgroup.c 2013-10-15 11:24:06.000000000 +0800
@@ -86,6 +86,13 @@ EXPORT_SYMBOL_GPL(cgroup_mutex); /* only
static DEFINE_MUTEX(cgroup_mutex);
#endif
+void cgroup_lock(void)
+{
+ mutex_lock(&cgroup_mutex);
+ pr_info("cgroup_lock: %d (%s)\n", task_tgid_nr(current), current->comm);
+ dump_stack();
+}
+
static DEFINE_MUTEX(cgroup_root_mutex);
/*
@@ -316,7 +323,7 @@ static inline struct cftype *__d_cft(str
*/
static bool cgroup_lock_live_group(struct cgroup *cgrp)
{
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
if (cgroup_is_dead(cgrp)) {
mutex_unlock(&cgroup_mutex);
return false;
@@ -847,7 +854,7 @@ static void cgroup_free_fn(struct work_s
struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
struct cgroup_subsys *ss;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
/*
* Release the subsystem state objects.
*/
@@ -1324,7 +1331,7 @@ static void drop_parsed_module_refcounts
struct cgroup_subsys *ss;
int i;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
for_each_subsys(ss, i)
if (subsys_mask & (1UL << i))
module_put(cgroup_subsys[i]->module);
@@ -1345,7 +1352,7 @@ static int cgroup_remount(struct super_b
}
mutex_lock(&cgrp->dentry->d_inode->i_mutex);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
mutex_lock(&cgroup_root_mutex);
/* See what subsystems are wanted */
@@ -1587,7 +1594,7 @@ static struct dentry *cgroup_mount(struc
struct inode *inode;
/* First find the desired set of subsystems */
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
ret = parse_cgroupfs_options(data, &opts);
mutex_unlock(&cgroup_mutex);
if (ret)
@@ -1631,7 +1638,7 @@ static struct dentry *cgroup_mount(struc
inode = sb->s_root->d_inode;
mutex_lock(&inode->i_mutex);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
mutex_lock(&cgroup_root_mutex);
/* Check for name clashes with existing mounts */
@@ -1746,7 +1753,7 @@ static void cgroup_kill_sb(struct super_
BUG_ON(root->number_of_cgroups != 1);
BUG_ON(!list_empty(&cgrp->children));
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
mutex_lock(&cgroup_root_mutex);
/* Rebind all subsystems back to the default hierarchy */
@@ -1866,7 +1873,7 @@ int task_cgroup_path(struct task_struct
if (buflen < 2)
return -ENAMETOOLONG;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id);
@@ -2251,7 +2258,7 @@ int cgroup_attach_task_all(struct task_s
struct cgroupfs_root *root;
int retval = 0;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
for_each_active_root(root) {
struct cgroup *from_cg = task_cgroup_from_root(from, root);
@@ -2819,7 +2826,7 @@ static void cgroup_cfts_prepare(void)
* Instead, we use cgroup_for_each_descendant_pre() and drop RCU
* read lock before calling cgroup_addrm_files().
*/
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
}
static void cgroup_cfts_commit(struct cgroup_subsys *ss,
@@ -2852,7 +2859,7 @@ static void cgroup_cfts_commit(struct cg
/* @root always needs to be updated */
inode = root->dentry->d_inode;
mutex_lock(&inode->i_mutex);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
cgroup_addrm_files(root, ss, cfts, is_add);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&inode->i_mutex);
@@ -2871,7 +2878,7 @@ static void cgroup_cfts_commit(struct cg
prev = cgrp->dentry;
mutex_lock(&inode->i_mutex);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp))
cgroup_addrm_files(cgrp, ss, cfts, is_add);
mutex_unlock(&cgroup_mutex);
@@ -3406,7 +3413,7 @@ static void cgroup_transfer_one_task(str
{
struct cgroup *new_cgroup = scan->data;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
cgroup_attach_task(new_cgroup, task, false);
mutex_unlock(&cgroup_mutex);
}
@@ -4596,7 +4603,7 @@ static void cgroup_offline_fn(struct wor
struct dentry *d = cgrp->dentry;
struct cgroup_subsys *ss;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
/*
* css_tryget() is guaranteed to fail now. Tell subsystems to
@@ -4630,7 +4637,7 @@ static int cgroup_rmdir(struct inode *un
{
int ret;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
ret = cgroup_destroy_locked(dentry->d_fsdata);
mutex_unlock(&cgroup_mutex);
@@ -4657,7 +4664,7 @@ static void __init cgroup_init_subsys(st
printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
/* init base cftset */
cgroup_init_cftsets(ss);
@@ -4736,7 +4743,7 @@ int __init_or_module cgroup_load_subsys(
/* init base cftset */
cgroup_init_cftsets(ss);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
cgroup_subsys[ss->subsys_id] = ss;
/*
@@ -4824,7 +4831,7 @@ void cgroup_unload_subsys(struct cgroup_
*/
BUG_ON(ss->root != &cgroup_dummy_root);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
offline_css(ss, cgroup_dummy_top);
@@ -4934,7 +4941,7 @@ int __init cgroup_init(void)
}
/* allocate id for the dummy hierarchy */
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
mutex_lock(&cgroup_root_mutex);
/* Add init_css_set to the hash table */
@@ -5001,7 +5008,7 @@ int proc_cgroup_show(struct seq_file *m,
retval = 0;
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
for_each_active_root(root) {
struct cgroup_subsys *ss;
@@ -5044,7 +5051,7 @@ static int proc_cgroupstats_show(struct
* cgroup_mutex is also necessary to guarantee an atomic snapshot of
* subsys/hierarchy state.
*/
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
for_each_subsys(ss, i)
seq_printf(m, "%s\t%d\t%d\t%d\n",
@@ -5273,7 +5280,7 @@ static void check_for_release(struct cgr
static void cgroup_release_agent(struct work_struct *work)
{
BUG_ON(work != &release_agent_work);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
raw_spin_lock(&release_list_lock);
while (!list_empty(&release_list)) {
char *argv[3], *envp[3];
@@ -5309,7 +5316,7 @@ static void cgroup_release_agent(struct
* be a slow process */
mutex_unlock(&cgroup_mutex);
call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
- mutex_lock(&cgroup_mutex);
+ cgroup_lock();
continue_free:
kfree(pathbuf);
kfree(agentbuf);
--
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