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authorPaul Menage <menage@google.com>2007-10-18 23:39:38 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-19 11:53:36 -0700
commit81a6a5cdd2c5cd70874b88afe524ab09e9e869af (patch)
treeba46c47a0692b687a96e52e61bfda4f14457017f /kernel/cgroup.c
parent817929ec274bcfe771586d338bb31d1659615686 (diff)
Task Control Groups: automatic userspace notification of idle cgroups
Add the following files to the cgroup filesystem: notify_on_release - configures/reports whether the cgroup subsystem should attempt to run a release script when this cgroup becomes unused release_agent - configures/reports the release agent to be used for this hierarchy (top level in each hierarchy only) releasable - reports whether this cgroup would have been auto-released if notify_on_release was true and a release agent was configured (mainly useful for debugging) To avoid locking issues, invoking the userspace release agent is done via a workqueue task; cgroups that need to have their release agents invoked by the workqueue task are linked on to a list. [pj@sgi.com: Need to include kmod.h] Signed-off-by: Paul Menage <menage@google.com> Cc: Serge E. Hallyn <serue@us.ibm.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Dave Hansen <haveblue@us.ibm.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Paul Jackson <pj@sgi.com> Cc: Kirill Korotaev <dev@openvz.org> Cc: Herbert Poetzl <herbert@13thfloor.at> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Paul Jackson <pj@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c428
1 files changed, 386 insertions, 42 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 883928c0e147..d65a1246829f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -43,8 +43,11 @@
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/sort.h>
+#include <linux/kmod.h>
#include <asm/atomic.h>
+static DEFINE_MUTEX(cgroup_mutex);
+
/* Generate an array of cgroup subsystem pointers */
#define SUBSYS(_x) &_x ## _subsys,
@@ -83,6 +86,13 @@ struct cgroupfs_root {
/* Hierarchy-specific flags */
unsigned long flags;
+
+ /* The path to use for release notifications. No locking
+ * between setting and use - so if userspace updates this
+ * while child cgroups exist, you could miss a
+ * notification. We ensure that it's always a valid
+ * NUL-terminated string */
+ char release_agent_path[PATH_MAX];
};
@@ -110,7 +120,13 @@ static int need_forkexit_callback;
/* bits in struct cgroup flags field */
enum {
+ /* Control Group is dead */
CONT_REMOVED,
+ /* Control Group has previously had a child cgroup or a task,
+ * but no longer (only if CONT_NOTIFY_ON_RELEASE is set) */
+ CONT_RELEASABLE,
+ /* Control Group requires release notifications to userspace */
+ CONT_NOTIFY_ON_RELEASE,
};
/* convenient tests for these bits */
@@ -124,6 +140,19 @@ enum {
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
};
+inline int cgroup_is_releasable(const struct cgroup *cont)
+{
+ const int bits =
+ (1 << CONT_RELEASABLE) |
+ (1 << CONT_NOTIFY_ON_RELEASE);
+ return (cont->flags & bits) == bits;
+}
+
+inline int notify_on_release(const struct cgroup *cont)
+{
+ return test_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags);
+}
+
/*
* for_each_subsys() allows you to iterate on each subsystem attached to
* an active hierarchy
@@ -135,6 +164,14 @@ list_for_each_entry(_ss, &_root->subsys_list, sibling)
#define for_each_root(_root) \
list_for_each_entry(_root, &roots, root_list)
+/* the list of cgroups eligible for automatic release. Protected by
+ * release_list_lock */
+static LIST_HEAD(release_list);
+static DEFINE_SPINLOCK(release_list_lock);
+static void cgroup_release_agent(struct work_struct *work);
+static DECLARE_WORK(release_agent_work, cgroup_release_agent);
+static void check_for_release(struct cgroup *cont);
+
/* Link structure for associating css_set objects with cgroups */
struct cg_cgroup_link {
/*
@@ -189,11 +226,8 @@ static int use_task_css_set_links;
/*
* unlink a css_set from the list and free it
*/
-static void release_css_set(struct kref *k)
+static void unlink_css_set(struct css_set *cg)
{
- struct css_set *cg = container_of(k, struct css_set, ref);
- int i;
-
write_lock(&css_set_lock);
list_del(&cg->list);
css_set_count--;
@@ -206,11 +240,39 @@ static void release_css_set(struct kref *k)
kfree(link);
}
write_unlock(&css_set_lock);
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)
- atomic_dec(&cg->subsys[i]->cgroup->count);
+}
+
+static void __release_css_set(struct kref *k, int taskexit)
+{
+ int i;
+ struct css_set *cg = container_of(k, struct css_set, ref);
+
+ unlink_css_set(cg);
+
+ rcu_read_lock();
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ struct cgroup *cont = cg->subsys[i]->cgroup;
+ if (atomic_dec_and_test(&cont->count) &&
+ notify_on_release(cont)) {
+ if (taskexit)
+ set_bit(CONT_RELEASABLE, &cont->flags);
+ check_for_release(cont);
+ }
+ }
+ rcu_read_unlock();
kfree(cg);
}
+static void release_css_set(struct kref *k)
+{
+ __release_css_set(k, 0);
+}
+
+static void release_css_set_taskexit(struct kref *k)
+{
+ __release_css_set(k, 1);
+}
+
/*
* refcounted get/put for css_set objects
*/
@@ -224,6 +286,11 @@ static inline void put_css_set(struct css_set *cg)
kref_put(&cg->ref, release_css_set);
}
+static inline void put_css_set_taskexit(struct css_set *cg)
+{
+ kref_put(&cg->ref, release_css_set_taskexit);
+}
+
/*
* find_existing_css_set() is a helper for
* find_css_set(), and checks to see whether an existing
@@ -465,8 +532,6 @@ static struct css_set *find_css_set(
* update of a tasks cgroup pointer by attach_task()
*/
-static DEFINE_MUTEX(cgroup_mutex);
-
/**
* cgroup_lock - lock out any changes to cgroup structures
*
@@ -526,6 +591,13 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
if (S_ISDIR(inode->i_mode)) {
struct cgroup *cont = dentry->d_fsdata;
BUG_ON(!(cgroup_is_removed(cont)));
+ /* It's possible for external users to be holding css
+ * reference counts on a cgroup; css_put() needs to
+ * be able to access the cgroup after decrementing
+ * the reference count in order to know if it needs to
+ * queue the cgroup to be handled by the release
+ * agent */
+ synchronize_rcu();
kfree(cont);
}
iput(inode);
@@ -657,6 +729,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
seq_printf(seq, ",%s", ss->name);
if (test_bit(ROOT_NOPREFIX, &root->flags))
seq_puts(seq, ",noprefix");
+ if (strlen(root->release_agent_path))
+ seq_printf(seq, ",release_agent=%s", root->release_agent_path);
mutex_unlock(&cgroup_mutex);
return 0;
}
@@ -664,6 +738,7 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
struct cgroup_sb_opts {
unsigned long subsys_bits;
unsigned long flags;
+ char *release_agent;
};
/* Convert a hierarchy specifier into a bitmask of subsystems and
@@ -675,6 +750,7 @@ static int parse_cgroupfs_options(char *data,
opts->subsys_bits = 0;
opts->flags = 0;
+ opts->release_agent = NULL;
while ((token = strsep(&o, ",")) != NULL) {
if (!*token)
@@ -683,6 +759,15 @@ static int parse_cgroupfs_options(char *data,
opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
} else if (!strcmp(token, "noprefix")) {
set_bit(ROOT_NOPREFIX, &opts->flags);
+ } else if (!strncmp(token, "release_agent=", 14)) {
+ /* Specifying two release agents is forbidden */
+ if (opts->release_agent)
+ return -EINVAL;
+ opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
+ if (!opts->release_agent)
+ return -ENOMEM;
+ strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
+ opts->release_agent[PATH_MAX - 1] = 0;
} else {
struct cgroup_subsys *ss;
int i;
@@ -732,7 +817,11 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (!ret)
cgroup_populate_dir(cont);
+ if (opts.release_agent)
+ strcpy(root->release_agent_path, opts.release_agent);
out_unlock:
+ if (opts.release_agent)
+ kfree(opts.release_agent);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&cont->dentry->d_inode->i_mutex);
return ret;
@@ -756,6 +845,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
INIT_LIST_HEAD(&cont->sibling);
INIT_LIST_HEAD(&cont->children);
INIT_LIST_HEAD(&cont->css_sets);
+ INIT_LIST_HEAD(&cont->release_list);
}
static int cgroup_test_super(struct super_block *sb, void *data)
@@ -830,8 +920,11 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
/* First find the desired set of subsystems */
ret = parse_cgroupfs_options(data, &opts);
- if (ret)
+ if (ret) {
+ if (opts.release_agent)
+ kfree(opts.release_agent);
return ret;
+ }
root = kzalloc(sizeof(*root), GFP_KERNEL);
if (!root)
@@ -840,6 +933,10 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
init_cgroup_root(root);
root->subsys_bits = opts.subsys_bits;
root->flags = opts.flags;
+ if (opts.release_agent) {
+ strcpy(root->release_agent_path, opts.release_agent);
+ kfree(opts.release_agent);
+ }
sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
@@ -1120,7 +1217,7 @@ static int attach_task(struct cgroup *cont, struct task_struct *tsk)
ss->attach(ss, cont, oldcont, tsk);
}
}
-
+ set_bit(CONT_RELEASABLE, &oldcont->flags);
synchronize_rcu();
put_css_set(cg);
return 0;
@@ -1170,6 +1267,9 @@ enum cgroup_filetype {
FILE_ROOT,
FILE_DIR,
FILE_TASKLIST,
+ FILE_NOTIFY_ON_RELEASE,
+ FILE_RELEASABLE,
+ FILE_RELEASE_AGENT,
};
static ssize_t cgroup_write_uint(struct cgroup *cont, struct cftype *cft,
@@ -1240,6 +1340,32 @@ static ssize_t cgroup_common_file_write(struct cgroup *cont,
case FILE_TASKLIST:
retval = attach_task_by_pid(cont, buffer);
break;
+ case FILE_NOTIFY_ON_RELEASE:
+ clear_bit(CONT_RELEASABLE, &cont->flags);
+ if (simple_strtoul(buffer, NULL, 10) != 0)
+ set_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags);
+ else
+ clear_bit(CONT_NOTIFY_ON_RELEASE, &cont->flags);
+ break;
+ case FILE_RELEASE_AGENT:
+ {
+ struct cgroupfs_root *root = cont->root;
+ /* Strip trailing newline */
+ if (nbytes && (buffer[nbytes-1] == '\n')) {
+ buffer[nbytes-1] = 0;
+ }
+ if (nbytes < sizeof(root->release_agent_path)) {
+ /* We never write anything other than '\0'
+ * into the last char of release_agent_path,
+ * so it always remains a NUL-terminated
+ * string */
+ strncpy(root->release_agent_path, buffer, nbytes);
+ root->release_agent_path[nbytes] = 0;
+ } else {
+ retval = -ENOSPC;
+ }
+ break;
+ }
default:
retval = -EINVAL;
goto out2;
@@ -1281,6 +1407,49 @@ static ssize_t cgroup_read_uint(struct cgroup *cont, struct cftype *cft,
return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}
+static ssize_t cgroup_common_file_read(struct cgroup *cont,
+ struct cftype *cft,
+ struct file *file,
+ char __user *buf,
+ size_t nbytes, loff_t *ppos)
+{
+ enum cgroup_filetype type = cft->private;
+ char *page;
+ ssize_t retval = 0;
+ char *s;
+
+ if (!(page = (char *)__get_free_page(GFP_KERNEL)))
+ return -ENOMEM;
+
+ s = page;
+
+ switch (type) {
+ case FILE_RELEASE_AGENT:
+ {
+ struct cgroupfs_root *root;
+ size_t n;
+ mutex_lock(&cgroup_mutex);
+ root = cont->root;
+ n = strnlen(root->release_agent_path,
+ sizeof(root->release_agent_path));
+ n = min(n, (size_t) PAGE_SIZE);
+ strncpy(s, root->release_agent_path, n);
+ mutex_unlock(&cgroup_mutex);
+ s += n;
+ break;
+ }
+ default:
+ retval = -EINVAL;
+ goto out;
+ }
+ *s++ = '\n';
+
+ retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
+out:
+ free_page((unsigned long)page);
+ return retval;
+}
+
static ssize_t cgroup_file_read(struct file *file, char __user *buf,
size_t nbytes, loff_t *ppos)
{
@@ -1699,16 +1868,49 @@ static int cgroup_tasks_release(struct inode *unused_inode,
return 0;
}
+static u64 cgroup_read_notify_on_release(struct cgroup *cont,
+ struct cftype *cft)
+{
+ return notify_on_release(cont);
+}
+
+static u64 cgroup_read_releasable(struct cgroup *cont, struct cftype *cft)
+{
+ return test_bit(CONT_RELEASABLE, &cont->flags);
+}
+
/*
* for the common functions, 'private' gives the type of file
*/
-static struct cftype cft_tasks = {
- .name = "tasks",
- .open = cgroup_tasks_open,
- .read = cgroup_tasks_read,
+static struct cftype files[] = {
+ {
+ .name = "tasks",
+ .open = cgroup_tasks_open,
+ .read = cgroup_tasks_read,
+ .write = cgroup_common_file_write,
+ .release = cgroup_tasks_release,
+ .private = FILE_TASKLIST,
+ },
+
+ {
+ .name = "notify_on_release",
+ .read_uint = cgroup_read_notify_on_release,
+ .write = cgroup_common_file_write,
+ .private = FILE_NOTIFY_ON_RELEASE,
+ },
+
+ {
+ .name = "releasable",
+ .read_uint = cgroup_read_releasable,
+ .private = FILE_RELEASABLE,
+ }
+};
+
+static struct cftype cft_release_agent = {
+ .name = "release_agent",
+ .read = cgroup_common_file_read,
.write = cgroup_common_file_write,
- .release = cgroup_tasks_release,
- .private = FILE_TASKLIST,
+ .private = FILE_RELEASE_AGENT,
};
static int cgroup_populate_dir(struct cgroup *cont)
@@ -1719,10 +1921,15 @@ static int cgroup_populate_dir(struct cgroup *cont)
/* First clear out any existing files */
cgroup_clear_directory(cont->dentry);
- err = cgroup_add_file(cont, NULL, &cft_tasks);
+ err = cgroup_add_files(cont, NULL, files, ARRAY_SIZE(files));
if (err < 0)
return err;
+ if (cont == cont->top_cgroup) {
+ if ((err = cgroup_add_file(cont, NULL, &cft_release_agent)) < 0)
+ return err;
+ }
+
for_each_subsys(cont->root, ss) {
if (ss->populate && (err = ss->populate(ss, cont)) < 0)
return err;
@@ -1779,6 +1986,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
INIT_LIST_HEAD(&cont->sibling);
INIT_LIST_HEAD(&cont->children);
INIT_LIST_HEAD(&cont->css_sets);
+ INIT_LIST_HEAD(&cont->release_list);
cont->parent = parent;
cont->root = parent->root;
@@ -1840,6 +2048,38 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
return cgroup_create(c_parent, dentry, mode | S_IFDIR);
}
+static inline int cgroup_has_css_refs(struct cgroup *cont)
+{
+ /* Check the reference count on each subsystem. Since we
+ * already established that there are no tasks in the
+ * cgroup, if the css refcount is also 0, then there should
+ * be no outstanding references, so the subsystem is safe to
+ * destroy. We scan across all subsystems rather than using
+ * the per-hierarchy linked list of mounted subsystems since
+ * we can be called via check_for_release() with no
+ * synchronization other than RCU, and the subsystem linked
+ * list isn't RCU-safe */
+ int i;
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ struct cgroup_subsys *ss = subsys[i];
+ struct cgroup_subsys_state *css;
+ /* Skip subsystems not in this hierarchy */
+ if (ss->root != cont->root)
+ continue;
+ css = cont->subsys[ss->subsys_id];
+ /* When called from check_for_release() it's possible
+ * that by this point the cgroup has been removed
+ * and the css deleted. But a false-positive doesn't
+ * matter, since it can only happen if the cgroup
+ * has been deleted and hence no longer needs the
+ * release agent to be called anyway. */
+ if (css && atomic_read(&css->refcnt)) {
+ return 1;
+ }
+ }
+ return 0;
+}
+
static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
struct cgroup *cont = dentry->d_fsdata;
@@ -1848,7 +2088,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
struct cgroup_subsys *ss;
struct super_block *sb;
struct cgroupfs_root *root;
- int css_busy = 0;
/* the vfs holds both inode->i_mutex already */
@@ -1866,20 +2105,7 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
root = cont->root;
sb = root->sb;
- /* Check the reference count on each subsystem. Since we
- * already established that there are no tasks in the
- * cgroup, if the css refcount is also 0, then there should
- * be no outstanding references, so the subsystem is safe to
- * destroy */
- for_each_subsys(root, ss) {
- struct cgroup_subsys_state *css;
- css = cont->subsys[ss->subsys_id];
- if (atomic_read(&css->refcnt)) {
- css_busy = 1;
- break;
- }
- }
- if (css_busy) {
+ if (cgroup_has_css_refs(cont)) {
mutex_unlock(&cgroup_mutex);
return -EBUSY;
}
@@ -1889,7 +2115,11 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
ss->destroy(ss, cont);
}
+ spin_lock(&release_list_lock);
set_bit(CONT_REMOVED, &cont->flags);
+ if (!list_empty(&cont->release_list))
+ list_del(&cont->release_list);
+ spin_unlock(&release_list_lock);
/* delete my sibling from parent->children */
list_del(&cont->sibling);
spin_lock(&cont->dentry->d_lock);
@@ -1901,6 +2131,9 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
dput(d);
root->number_of_cgroups--;
+ set_bit(CONT_RELEASABLE, &parent->flags);
+ check_for_release(parent);
+
mutex_unlock(&cgroup_mutex);
/* Drop the active superblock reference that we took when we
* created the cgroup */
@@ -1938,15 +2171,15 @@ static void cgroup_init_subsys(struct cgroup_subsys *ss)
/* If this subsystem requested that it be notified with fork
* events, we should send it one now for every process in the
* system */
- if (ss->fork) {
- struct task_struct *g, *p;
-
- read_lock(&tasklist_lock);
- do_each_thread(g, p) {
- ss->fork(ss, p);
- } while_each_thread(g, p);
- read_unlock(&tasklist_lock);
- }
+ if (ss->fork) {
+ struct task_struct *g, *p;
+
+ read_lock(&tasklist_lock);
+ do_each_thread(g, p) {
+ ss->fork(ss, p);
+ } while_each_thread(g, p);
+ read_unlock(&tasklist_lock);
+ }
need_forkexit_callback |= ss->fork || ss->exit;
@@ -2263,7 +2496,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
tsk->cgroups = &init_css_set;
task_unlock(tsk);
if (cg)
- put_css_set(cg);
+ put_css_set_taskexit(cg);
}
/**
@@ -2374,7 +2607,10 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
out_release:
mutex_unlock(&inode->i_mutex);
+
+ mutex_lock(&cgroup_mutex);
put_css_set(cg);
+ mutex_unlock(&cgroup_mutex);
deactivate_super(parent->root->sb);
return ret;
}
@@ -2404,3 +2640,111 @@ int cgroup_is_descendant(const struct cgroup *cont)
ret = (cont == target);
return ret;
}
+
+static void check_for_release(struct cgroup *cont)
+{
+ /* All of these checks rely on RCU to keep the cgroup
+ * structure alive */
+ if (cgroup_is_releasable(cont) && !atomic_read(&cont->count)
+ && list_empty(&cont->children) && !cgroup_has_css_refs(cont)) {
+ /* Control Group is currently removeable. If it's not
+ * already queued for a userspace notification, queue
+ * it now */
+ int need_schedule_work = 0;
+ spin_lock(&release_list_lock);
+ if (!cgroup_is_removed(cont) &&
+ list_empty(&cont->release_list)) {
+ list_add(&cont->release_list, &release_list);
+ need_schedule_work = 1;
+ }
+ spin_unlock(&release_list_lock);
+ if (need_schedule_work)
+ schedule_work(&release_agent_work);
+ }
+}
+
+void __css_put(struct cgroup_subsys_state *css)
+{
+ struct cgroup *cont = css->cgroup;
+ rcu_read_lock();
+ if (atomic_dec_and_test(&css->refcnt) && notify_on_release(cont)) {
+ set_bit(CONT_RELEASABLE, &cont->flags);
+ check_for_release(cont);
+ }
+ rcu_read_unlock();
+}
+
+/*
+ * Notify userspace when a cgroup is released, by running the
+ * configured release agent with the name of the cgroup (path
+ * relative to the root of cgroup file system) as the argument.
+ *
+ * Most likely, this user command will try to rmdir this cgroup.
+ *
+ * This races with the possibility that some other task will be
+ * attached to this cgroup before it is removed, or that some other
+ * user task will 'mkdir' a child cgroup of this cgroup. That's ok.
+ * The presumed 'rmdir' will fail quietly if this cgroup is no longer
+ * unused, and this cgroup will be reprieved from its death sentence,
+ * to continue to serve a useful existence. Next time it's released,
+ * we will get notified again, if it still has 'notify_on_release' set.
+ *
+ * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
+ * means only wait until the task is successfully execve()'d. The
+ * separate release agent task is forked by call_usermodehelper(),
+ * then control in this thread returns here, without waiting for the
+ * release agent task. We don't bother to wait because the caller of
+ * this routine has no use for the exit status of the release agent
+ * task, so no sense holding our caller up for that.
+ *
+ */
+
+static void cgroup_release_agent(struct work_struct *work)
+{
+ BUG_ON(work != &release_agent_work);
+ mutex_lock(&cgroup_mutex);
+ spin_lock(&release_list_lock);
+ while (!list_empty(&release_list)) {
+ char *argv[3], *envp[3];
+ int i;
+ char *pathbuf;
+ struct cgroup *cont = list_entry(release_list.next,
+ struct cgroup,
+ release_list);
+ list_del_init(&cont->release_list);
+ spin_unlock(&release_list_lock);
+ pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!pathbuf) {
+ spin_lock(&release_list_lock);
+ continue;
+ }
+
+ if (cgroup_path(cont, pathbuf, PAGE_SIZE) < 0) {
+ kfree(pathbuf);
+ spin_lock(&release_list_lock);
+ continue;
+ }
+
+ i = 0;
+ argv[i++] = cont->root->release_agent_path;
+ argv[i++] = (char *)pathbuf;
+ argv[i] = NULL;
+
+ i = 0;
+ /* minimal command environment */
+ envp[i++] = "HOME=/";
+ envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
+ envp[i] = NULL;
+
+ /* Drop the lock while we invoke the usermode helper,
+ * since the exec could involve hitting disk and hence
+ * be a slow process */
+ mutex_unlock(&cgroup_mutex);
+ call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+ kfree(pathbuf);
+ mutex_lock(&cgroup_mutex);
+ spin_lock(&release_list_lock);
+ }
+ spin_unlock(&release_list_lock);
+ mutex_unlock(&cgroup_mutex);
+}

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