[PATCH 6/8] cgroup: remove cgroup->name

From: Tejun Heo
Date: Tue Jan 28 2014 - 19:01:05 EST

cgroup->name handling became quite complicated over time involving
dedicated struct cgroup_name for RCU protection. Now that cgroup is
on kernfs, we can drop all of it and simply use kernfs_name/path() and
friends. Replace cgroup->name and all related code with kernfs
name/path constructs.

* Reimplement cgroup_name() and cgroup_path() as thin wrappers on top
of kernfs counterparts, which involves semantic changes.
pr_cont_cgroup_name() and pr_cont_cgroup_path() added.

* cgroup->name handling dropped from cgroup_rename().

* All users of cgroup_name/path() updated to the new semantics. Users
which were formatting the string just to printk them are converted
to use pr_cont_cgroup_name/path() instead, which simplifies things
quite a bit. As cgroup_name() no longer requires RCU read lock
around it, RCU lockings which were protecting only cgroup_name() are
removed.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
block/blk-cgroup.h | 12 ++--
fs/kernfs/dir.c | 1 +
include/linux/cgroup.h | 55 +++++++++---------
kernel/cgroup.c | 148 ++++++++++++-------------------------------------
kernel/cpuset.c | 27 +++++----
kernel/sched/debug.c | 3 +-
mm/memcontrol.c | 63 ++++++---------------
7 files changed, 102 insertions(+), 207 deletions(-)

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 453b528..15a8d64 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -241,12 +241,16 @@ static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
*/
static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
{
- int ret;
+ char *p;

- ret = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
- if (ret)
+ p = cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
+ if (!p) {
strncpy(buf, "<unavailable>", buflen);
- return ret;
+ return -ENAMETOOLONG;
+ }
+
+ memmove(buf, p, buf + buflen - p);
+ return 0;
}

/**
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index a347792..939684e 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -112,6 +112,7 @@ char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
spin_unlock_irqrestore(&kernfs_rename_lock, flags);
return p;
}
+EXPORT_SYMBOL_GPL(kernfs_path);

/**
* pr_cont_kernfs_name - pr_cont name of a kernfs_node
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 3c0c7e4..8202abb 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -138,11 +138,6 @@ enum {
CGRP_SANE_BEHAVIOR,
};

-struct cgroup_name {
- struct rcu_head rcu_head;
- char name[];
-};
-
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */

@@ -177,19 +172,6 @@ struct cgroup {
*/
u64 serial_nr;

- /*
- * This is a copy of dentry->d_name, and it's needed because
- * we can't use dentry->d_name in cgroup_path().
- *
- * You must acquire rcu_read_lock() to access cgrp->name, and
- * the only place that can change it is rename(), which is
- * protected by parent dir's i_mutex.
- *
- * Normally you should use cgroup_name() wrapper rather than
- * access it directly.
- */
- struct cgroup_name __rcu *name;
-
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];

@@ -477,12 +459,6 @@ static inline bool cgroup_sane_behavior(const struct cgroup *cgrp)
return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR;
}

-/* Caller should hold rcu_read_lock() */
-static inline const char *cgroup_name(const struct cgroup *cgrp)
-{
- return rcu_dereference(cgrp->name)->name;
-}
-
/* returns ino associated with a cgroup, 0 indicates unmounted root */
static inline ino_t cgroup_ino(struct cgroup *cgrp)
{
@@ -501,14 +477,39 @@ static inline struct cftype *seq_cft(struct seq_file *seq)

struct cgroup_subsys_state *seq_css(struct seq_file *seq);

+/*
+ * Name / path handling functions. All are thin wrappers around the kernfs
+ * counterparts and can be called under any context.
+ */
+
+static inline int cgroup_name(struct cgroup *cgrp, char *buf, size_t buflen)
+{
+ return kernfs_name(cgrp->kn, buf, buflen);
+}
+
+static inline char * __must_check cgroup_path(struct cgroup *cgrp, char *buf,
+ size_t buflen)
+{
+ return kernfs_path(cgrp->kn, buf, buflen);
+}
+
+static inline void pr_cont_cgroup_name(struct cgroup *cgrp)
+{
+ pr_cont_kernfs_name(cgrp->kn);
+}
+
+static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
+{
+ pr_cont_kernfs_path(cgrp->kn);
+}
+
+char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
+
int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
int cgroup_rm_cftypes(struct cftype *cfts);

bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);

-int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);
-int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
-
int cgroup_task_count(const struct cgroup *cgrp);

/*
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 3e4df3c..397aca3 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -145,8 +145,6 @@ static int cgroup_root_count;
/* hierarchy ID allocation and mapping, protected by cgroup_mutex */
static DEFINE_IDR(cgroup_hierarchy_idr);

-static struct cgroup_name root_cgroup_name = { .name = "/" };
-
/*
* Assign a monotonically increasing serial number to cgroups. It
* guarantees cgroups with bigger numbers are newer than those with smaller
@@ -888,17 +886,6 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask);
static struct kernfs_syscall_ops cgroup_kf_syscall_ops;
static const struct file_operations proc_cgroupstats_operations;

-static struct cgroup_name *cgroup_alloc_name(const char *name_str)
-{
- struct cgroup_name *name;
-
- name = kmalloc(sizeof(*name) + strlen(name_str) + 1, GFP_KERNEL);
- if (!name)
- return NULL;
- strcpy(name->name, name_str);
- return name;
-}
-
static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
char *buf)
{
@@ -958,8 +945,6 @@ static void cgroup_free_fn(struct work_struct *work)
cgroup_pidlist_destroy_all(cgrp);

kernfs_put(cgrp->kn);
-
- kfree(rcu_dereference_raw(cgrp->name));
kfree(cgrp);
}

@@ -1375,7 +1360,6 @@ static void init_cgroup_root(struct cgroupfs_root *root)
INIT_LIST_HEAD(&root->root_list);
root->number_of_cgroups = 1;
cgrp->root = root;
- RCU_INIT_POINTER(cgrp->name, &root_cgroup_name);
init_cgroup_housekeeping(cgrp);
idr_init(&root->cgroup_idr);
}
@@ -1580,57 +1564,6 @@ static struct file_system_type cgroup_fs_type = {
static struct kobject *cgroup_kobj;

/**
- * cgroup_path - generate the path of a cgroup
- * @cgrp: the cgroup in question
- * @buf: the buffer to write the path into
- * @buflen: the length of the buffer
- *
- * Writes path of cgroup into buf. Returns 0 on success, -errno on error.
- *
- * We can't generate cgroup path using dentry->d_name, as accessing
- * dentry->name must be protected by irq-unsafe dentry->d_lock or parent
- * inode's i_mutex, while on the other hand cgroup_path() can be called
- * with some irq-safe spinlocks held.
- */
-int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
-{
- int ret = -ENAMETOOLONG;
- char *start;
-
- if (!cgrp->parent) {
- if (strlcpy(buf, "/", buflen) >= buflen)
- return -ENAMETOOLONG;
- return 0;
- }
-
- start = buf + buflen - 1;
- *start = '\0';
-
- rcu_read_lock();
- do {
- const char *name = cgroup_name(cgrp);
- int len;
-
- len = strlen(name);
- if ((start -= len) < buf)
- goto out;
- memcpy(start, name, len);
-
- if (--start < buf)
- goto out;
- *start = '/';
-
- cgrp = cgrp->parent;
- } while (cgrp->parent);
- ret = 0;
- memmove(buf, start, buf + buflen - start);
-out:
- rcu_read_unlock();
- return ret;
-}
-EXPORT_SYMBOL_GPL(cgroup_path);
-
-/**
* task_cgroup_path - cgroup path of a task in the first cgroup hierarchy
* @task: target task
* @buf: the buffer to write the path into
@@ -1641,16 +1574,14 @@ EXPORT_SYMBOL_GPL(cgroup_path);
* function grabs cgroup_mutex and shouldn't be used inside locks used by
* cgroup controller callbacks.
*
- * Returns 0 on success, fails with -%ENAMETOOLONG if @buflen is too short.
+ * Return value is the same as kernfs_path().
*/
-int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
+char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
{
struct cgroupfs_root *root;
struct cgroup *cgrp;
- int hierarchy_id = 1, ret = 0;
-
- if (buflen < 2)
- return -ENAMETOOLONG;
+ int hierarchy_id = 1;
+ char *path = NULL;

mutex_lock(&cgroup_mutex);

@@ -1658,14 +1589,15 @@ int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)

if (root) {
cgrp = task_cgroup_from_root(task, root);
- ret = cgroup_path(cgrp, buf, buflen);
+ path = cgroup_path(cgrp, buf, buflen);
} else {
/* if no hierarchy exists, everyone is in "/" */
- memcpy(buf, "/", 2);
+ if (strlcpy(buf, "/", buflen) < buflen)
+ path = buf;
}

mutex_unlock(&cgroup_mutex);
- return ret;
+ return path;
}
EXPORT_SYMBOL_GPL(task_cgroup_path);

@@ -2193,7 +2125,6 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
const char *new_name_str)
{
struct cgroup *cgrp = kn->priv;
- struct cgroup_name *name, *old_name;
int ret;

if (kernfs_type(kn) != KERNFS_DIR)
@@ -2208,25 +2139,13 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
if (cgroup_sane_behavior(cgrp))
return -EPERM;

- name = cgroup_alloc_name(new_name_str);
- if (!name)
- return -ENOMEM;
-
mutex_lock(&cgroup_tree_mutex);
mutex_lock(&cgroup_mutex);

ret = kernfs_rename(kn, new_parent, new_name_str);
- if (!ret) {
- old_name = rcu_dereference_protected(cgrp->name, true);
- rcu_assign_pointer(cgrp->name, name);
- } else {
- old_name = name;
- }

mutex_unlock(&cgroup_mutex);
mutex_unlock(&cgroup_tree_mutex);
-
- kfree_rcu(old_name, rcu_head);
return ret;
}

@@ -3701,14 +3620,13 @@ err_free:
/**
* cgroup_create - create a cgroup
* @parent: cgroup that will be parent of the new cgroup
- * @name_str: name of the new cgroup
+ * @name: name of the new cgroup
* @mode: mode to set on new cgroup
*/
-static long cgroup_create(struct cgroup *parent, const char *name_str,
+static long cgroup_create(struct cgroup *parent, const char *name,
umode_t mode)
{
struct cgroup *cgrp;
- struct cgroup_name *name;
struct cgroupfs_root *root = parent->root;
int ssid, err;
struct cgroup_subsys *ss;
@@ -3719,13 +3637,6 @@ static long cgroup_create(struct cgroup *parent, const char *name_str,
if (!cgrp)
return -ENOMEM;

- name = cgroup_alloc_name(name_str);
- if (!name) {
- err = -ENOMEM;
- goto err_free_cgrp;
- }
- rcu_assign_pointer(cgrp->name, name);
-
/*
* Temporarily set the pointer to NULL, so idr_find() won't return
* a half-baked cgroup.
@@ -3733,7 +3644,7 @@ static long cgroup_create(struct cgroup *parent, const char *name_str,
cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL);
if (cgrp->id < 0) {
err = -ENOMEM;
- goto err_free_name;
+ goto err_free_cgrp;
}

mutex_lock(&cgroup_tree_mutex);
@@ -3763,7 +3674,7 @@ static long cgroup_create(struct cgroup *parent, const char *name_str,
set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags);

/* create the directory */
- kn = kernfs_create_dir(parent->kn, name->name, mode, cgrp);
+ kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
if (IS_ERR(kn)) {
err = PTR_ERR(kn);
goto err_unlock;
@@ -3820,8 +3731,6 @@ err_unlock:
err_unlock_tree:
mutex_unlock(&cgroup_tree_mutex);
idr_remove(&root->cgroup_idr, cgrp->id);
-err_free_name:
- kfree(rcu_dereference_raw(cgrp->name));
err_free_cgrp:
kfree(cgrp);
return err;
@@ -4282,12 +4191,12 @@ int proc_cgroup_show(struct seq_file *m, void *v)
{
struct pid *pid;
struct task_struct *tsk;
- char *buf;
+ char *buf, *path;
int retval;
struct cgroupfs_root *root;

retval = -ENOMEM;
- buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf)
goto out;

@@ -4315,10 +4224,12 @@ int proc_cgroup_show(struct seq_file *m, void *v)
root->name);
seq_putc(m, ':');
cgrp = task_cgroup_from_root(tsk, root);
- retval = cgroup_path(cgrp, buf, PAGE_SIZE);
- if (retval < 0)
+ path = cgroup_path(cgrp, buf, PATH_MAX);
+ if (!path) {
+ retval = -ENAMETOOLONG;
goto out_unlock;
- seq_puts(m, buf);
+ }
+ seq_puts(m, path);
seq_putc(m, '\n');
}

@@ -4565,16 +4476,17 @@ static void cgroup_release_agent(struct work_struct *work)
while (!list_empty(&release_list)) {
char *argv[3], *envp[3];
int i;
- char *pathbuf = NULL, *agentbuf = NULL;
+ char *pathbuf = NULL, *agentbuf = NULL, *path;
struct cgroup *cgrp = list_entry(release_list.next,
struct cgroup,
release_list);
list_del_init(&cgrp->release_list);
raw_spin_unlock(&release_list_lock);
- pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!pathbuf)
goto continue_free;
- if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0)
+ path = cgroup_path(cgrp, pathbuf, PATH_MAX);
+ if (!path)
goto continue_free;
agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
if (!agentbuf)
@@ -4582,7 +4494,7 @@ static void cgroup_release_agent(struct work_struct *work)

i = 0;
argv[i++] = agentbuf;
- argv[i++] = pathbuf;
+ argv[i++] = path;
argv[i] = NULL;

i = 0;
@@ -4732,6 +4644,11 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
{
struct cgrp_cset_link *link;
struct css_set *cset;
+ char *name_buf;
+
+ name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+ if (!name_buf)
+ return -ENOMEM;

read_lock(&css_set_lock);
rcu_read_lock();
@@ -4740,14 +4657,17 @@ static int current_css_set_cg_links_read(struct seq_file *seq, void *v)
struct cgroup *c = link->cgrp;
const char *name = "?";

- if (c != cgroup_dummy_top)
- name = cgroup_name(c);
+ if (c != cgroup_dummy_top) {
+ cgroup_name(c, name_buf, NAME_MAX + 1);
+ name = name_buf;
+ }

seq_printf(seq, "Root %d group %s\n",
c->root->hierarchy_id, name);
}
rcu_read_unlock();
read_unlock(&css_set_lock);
+ kfree(name_buf);
return 0;
}

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 2d018c7..e97a6e8 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2088,10 +2088,9 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
parent = parent_cs(parent);

if (cgroup_transfer_tasks(parent->css.cgroup, cs->css.cgroup)) {
- rcu_read_lock();
- printk(KERN_ERR "cpuset: failed to transfer tasks out of empty cpuset %s\n",
- cgroup_name(cs->css.cgroup));
- rcu_read_unlock();
+ printk(KERN_ERR "cpuset: failed to transfer tasks out of empty cpuset ");
+ pr_cont_cgroup_name(cs->css.cgroup);
+ pr_cont("\n");
}
}

@@ -2619,19 +2618,17 @@ void cpuset_print_task_mems_allowed(struct task_struct *tsk)
/* Statically allocated to prevent using excess stack. */
static char cpuset_nodelist[CPUSET_NODELIST_LEN];
static DEFINE_SPINLOCK(cpuset_buffer_lock);
-
struct cgroup *cgrp = task_cs(tsk)->css.cgroup;

- rcu_read_lock();
spin_lock(&cpuset_buffer_lock);

nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
tsk->mems_allowed);
- printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
- tsk->comm, cgroup_name(cgrp), cpuset_nodelist);
+ printk(KERN_INFO "%s cpuset=", tsk->comm);
+ pr_cont_cgroup_name(cgrp);
+ pr_cont(" mems_allowed=%s\n", cpuset_nodelist);

spin_unlock(&cpuset_buffer_lock);
- rcu_read_unlock();
}

/*
@@ -2681,12 +2678,12 @@ int proc_cpuset_show(struct seq_file *m, void *unused_v)
{
struct pid *pid;
struct task_struct *tsk;
- char *buf;
+ char *buf, *p;
struct cgroup_subsys_state *css;
int retval;

retval = -ENOMEM;
- buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf)
goto out;

@@ -2696,14 +2693,16 @@ int proc_cpuset_show(struct seq_file *m, void *unused_v)
if (!tsk)
goto out_free;

+ retval = -ENAMETOOLONG;
rcu_read_lock();
css = task_css(tsk, cpuset_cgrp_id);
- retval = cgroup_path(css->cgroup, buf, PAGE_SIZE);
+ p = cgroup_path(css->cgroup, buf, PATH_MAX);
rcu_read_unlock();
- if (retval < 0)
+ if (!p)
goto out_put_task;
- seq_puts(m, buf);
+ seq_puts(m, p);
seq_putc(m, '\n');
+ retval = 0;
out_put_task:
put_task_struct(tsk);
out_free:
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index dd52e7f..30eee3b 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -111,8 +111,7 @@ static char *task_group_path(struct task_group *tg)
if (autogroup_path(tg, group_path, PATH_MAX))
return group_path;

- cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
- return group_path;
+ return cgroup_path(tg->css.cgroup, group_path, PATH_MAX);
}
#endif

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ab4e412..1ac541a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1688,10 +1688,6 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
* interleave
*/
static DEFINE_SPINLOCK(oom_info_lock);
- struct cgroup *task_cgrp;
- struct cgroup *mem_cgrp;
- static char memcg_name[PATH_MAX];
- int ret;
struct mem_cgroup *iter;
unsigned int i;

@@ -1701,36 +1697,14 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
spin_lock(&oom_info_lock);
rcu_read_lock();

- mem_cgrp = memcg->css.cgroup;
- task_cgrp = task_cgroup(p, memory_cgrp_id);
+ pr_info("Task in ");
+ pr_cont_cgroup_path(task_cgroup(p, memory_cgrp_id));
+ pr_info(" killed as a result of limit of ");
+ pr_cont_cgroup_path(memcg->css.cgroup);
+ pr_info("\n");

- ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
- if (ret < 0) {
- /*
- * Unfortunately, we are unable to convert to a useful name
- * But we'll still print out the usage information
- */
- rcu_read_unlock();
- goto done;
- }
- rcu_read_unlock();
-
- pr_info("Task in %s killed", memcg_name);
-
- rcu_read_lock();
- ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
- if (ret < 0) {
- rcu_read_unlock();
- goto done;
- }
rcu_read_unlock();

- /*
- * Continues from above, so we don't need an KERN_ level
- */
- pr_cont(" as a result of limit of %s\n", memcg_name);
-done:
-
pr_info("memory: usage %llukB, limit %llukB, failcnt %llu\n",
res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
@@ -1745,13 +1719,8 @@ done:
res_counter_read_u64(&memcg->kmem, RES_FAILCNT));

for_each_mem_cgroup_tree(iter, memcg) {
- pr_info("Memory cgroup stats");
-
- rcu_read_lock();
- ret = cgroup_path(iter->css.cgroup, memcg_name, PATH_MAX);
- if (!ret)
- pr_cont(" for %s", memcg_name);
- rcu_read_unlock();
+ pr_info("Memory cgroup stats for ");
+ pr_cont_cgroup_path(iter->css.cgroup);
pr_cont(":");

for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
@@ -3401,7 +3370,7 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct kmem_cache *s)
{
struct kmem_cache *new;
- static char *tmp_name = NULL;
+ static char *tmp_path = NULL, *tmp_name = NULL;
static DEFINE_MUTEX(mutex); /* protects tmp_name */

BUG_ON(!memcg_can_account_kmem(memcg));
@@ -3413,18 +3382,20 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
* This static temporary buffer is used to prevent from
* pointless shortliving allocation.
*/
- if (!tmp_name) {
- tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
+ if (!tmp_path || !tmp_name) {
+ if (!tmp_path)
+ tmp_path = kmalloc(PATH_MAX, GFP_KERNEL);
if (!tmp_name)
+ tmp_name = kmalloc(NAME_MAX + 1, GFP_KERNEL);
+ if (!tmp_path || !tmp_name)
return NULL;
}

- rcu_read_lock();
- snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
- memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
- rcu_read_unlock();
+ cgroup_name(memcg->css.cgroup, tmp_name, NAME_MAX + 1);
+ snprintf(tmp_path, PATH_MAX, "%s(%d:%s)", s->name,
+ memcg_cache_id(memcg), tmp_name);

- new = kmem_cache_create_memcg(memcg, tmp_name, s->object_size, s->align,
+ new = kmem_cache_create_memcg(memcg, tmp_path, s->object_size, s->align,
(s->flags & ~SLAB_PANIC), s->ctor, s);

if (new)
--
1.8.5.3

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