[PATCH 07/10] Task Containers(V11): Automatic userspace notification of idle containers

menage
2007-07-20T19:46:35Z

[-- Attachment #1: containersv10-support-for-automatic-userspace-release-agents.patch --]
[-- Type: text/plain, Size: 22483 bytes --]

This patch adds the following files to the container filesystem:

notify_on_release - configures/reports whether the container subsystem should
attempt to run a release script when this container 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 container 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; containers that need to have their release agents invoked by
the workqueue task are linked on to a list.

Signed-off-by: Paul Menage <menage@google.com>
---

include/linux/container.h | 11 -
kernel/container.c | 425 +++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 393 insertions(+), 43 deletions(-)

Index: container-2.6.22-rc6-mm1/include/linux/container.h
===================================================================
--- container-2.6.22-rc6-mm1.orig/include/linux/container.h
+++ container-2.6.22-rc6-mm1/include/linux/container.h
@@ -77,10 +77,11 @@ static inline void css_get(struct contai
* css_get()
*/

+extern void __css_put(struct container_subsys_state *css);
static inline void css_put(struct container_subsys_state *css)
{
if (!test_bit(CSS_ROOT, &css->flags))
- atomic_dec(&css->refcnt);
+ __css_put(css);
}

struct container {
@@ -112,6 +113,13 @@ struct container {
* tasks in this container. Protected by css_group_lock
*/
struct list_head css_groups;
+
+ /*
+ * Linked list running through all containers that can
+ * potentially be reaped by the release agent. Protected by
+ * release_list_lock
+ */
+ struct list_head release_list;
};

/* A css_group is a structure holding pointers to a set of
@@ -285,7 +293,6 @@ struct task_struct *container_iter_next(
struct container_iter *it);
void container_iter_end(struct container *cont, struct container_iter *it);

-
#else /* !CONFIG_CONTAINERS */

static inline int container_init_early(void) { return 0; }
Index: container-2.6.22-rc6-mm1/kernel/container.c
===================================================================
--- container-2.6.22-rc6-mm1.orig/kernel/container.c
+++ container-2.6.22-rc6-mm1/kernel/container.c
@@ -44,6 +44,8 @@
#include <linux/sort.h>
#include <asm/atomic.h>

+static DEFINE_MUTEX(container_mutex);
+
/* Generate an array of container subsystem pointers */
#define SUBSYS(_x) &_x ## _subsys,

@@ -82,6 +84,13 @@ struct containerfs_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 subcontainers exist, you could miss a
+ * notification. We ensure that it's always a valid
+ * NUL-terminated string */
+ char release_agent_path[PATH_MAX];
};

@@ -109,7 +118,13 @@ static int need_forkexit_callback;

/* bits in struct container flags field */
enum {
+ /* Container is dead */
CONT_REMOVED,
+ /* Container has previously had a child container or a task,
+ * but no longer (only if CONT_NOTIFY_ON_RELEASE is set) */
+ CONT_RELEASABLE,
+ /* Container requires release notifications to userspace */
+ CONT_NOTIFY_ON_RELEASE,
};

/* convenient tests for these bits */
@@ -123,6 +138,19 @@ enum {
ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
};

+inline int container_is_releasable(const struct container *cont)
+{
+ const int bits =
+ (1 << CONT_RELEASABLE) |
+ (1 << CONT_NOTIFY_ON_RELEASE);
+ return (cont->flags & bits) == bits;
+}
+
+inline int notify_on_release(const struct container *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
@@ -134,6 +162,14 @@ list_for_each_entry(_ss, &_root->subsys_
#define for_each_root(_root) \
list_for_each_entry(_root, &roots, root_list)

+/* the list of containers eligible for automatic release. Protected by
+ * release_list_lock */
+static LIST_HEAD(release_list);
+static DEFINE_SPINLOCK(release_list_lock);
+static void container_release_agent(struct work_struct *work);
+static DECLARE_WORK(release_agent_work, container_release_agent);
+static void check_for_release(struct container *cont);
+
/* Link structure for associating css_group objects with containers */
struct cg_container_link {
/*
@@ -188,11 +224,8 @@ static int use_task_css_group_links;
/*
* unlink a css_group from the list and free it
*/
-static void release_css_group(struct kref *k)
+static void unlink_css_group(struct css_group *cg)
{
- struct css_group *cg = container_of(k, struct css_group, ref);
- int i;
-
write_lock(&css_group_lock);
list_del(&cg->list);
css_group_count--;
@@ -205,11 +238,39 @@ static void release_css_group(struct kre
kfree(link);
}
write_unlock(&css_group_lock);
- for (i = 0; i < CONTAINER_SUBSYS_COUNT; i++)
- atomic_dec(&cg->subsys[i]->container->count);
+}
+
+static void __release_css_group(struct kref *k, int taskexit)
+{
+ int i;
+ struct css_group *cg = container_of(k, struct css_group, ref);
+
+ unlink_css_group(cg);
+
+ rcu_read_lock();
+ for (i = 0; i < CONTAINER_SUBSYS_COUNT; i++) {
+ struct container *cont = cg->subsys[i]->container;
+ 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_group(struct kref *k)
+{
+ __release_css_group(k, 0);
+}
+
+static void release_css_group_taskexit(struct kref *k)
+{
+ __release_css_group(k, 1);
+}
+
/*
* refcounted get/put for css_group objects
*/
@@ -223,6 +284,11 @@ static inline void put_css_group(struct
kref_put(&cg->ref, release_css_group);
}

+static inline void put_css_group_taskexit(struct css_group *cg)
+{
+ kref_put(&cg->ref, release_css_group_taskexit);
+}
+
/*
* find_existing_css_group() is a helper for
* find_css_group(), and checks to see whether an existing
@@ -464,8 +530,6 @@ static struct css_group *find_css_group(
* update of a tasks container pointer by attach_task()
*/

-static DEFINE_MUTEX(container_mutex);
-
/**
* container_lock - lock out any changes to container structures
*
@@ -524,6 +588,13 @@ static void container_diput(struct dentr
if (S_ISDIR(inode->i_mode)) {
struct container *cont = dentry->d_fsdata;
BUG_ON(!(container_is_removed(cont)));
+ /* It's possible for external users to be holding css
+ * reference counts on a container; css_put() needs to
+ * be able to access the container after decrementing
+ * the reference count in order to know if it needs to
+ * queue the container to be handled by the release
+ * agent */
+ synchronize_rcu();
kfree(cont);
}
iput(inode);
@@ -668,6 +739,8 @@ static int container_show_options(struct
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(&container_mutex);
return 0;
}
@@ -675,6 +748,7 @@ static int container_show_options(struct
struct container_sb_opts {
unsigned long subsys_bits;
unsigned long flags;
+ char *release_agent;
};

/* Convert a hierarchy specifier into a bitmask of subsystems and
@@ -686,6 +760,7 @@ static int parse_containerfs_options(cha

opts->subsys_bits = 0;
opts->flags = 0;
+ opts->release_agent = NULL;

while ((token = strsep(&o, ",")) != NULL) {
if (!*token)
@@ -694,6 +769,15 @@ static int parse_containerfs_options(cha
opts->subsys_bits = (1 << CONTAINER_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 container_subsys *ss;
int i;
@@ -743,7 +827,11 @@ static int container_remount(struct supe
if (!ret)
container_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(&container_mutex);
mutex_unlock(&cont->dentry->d_inode->i_mutex);
return ret;
@@ -767,6 +855,7 @@ static void init_container_root(struct c
INIT_LIST_HEAD(&cont->sibling);
INIT_LIST_HEAD(&cont->children);
INIT_LIST_HEAD(&cont->css_groups);
+ INIT_LIST_HEAD(&cont->release_list);
}

static int container_test_super(struct super_block *sb, void *data)
@@ -841,8 +930,11 @@ static int container_get_sb(struct file_

/* First find the desired set of subsystems */
ret = parse_containerfs_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)
@@ -851,6 +943,10 @@ static int container_get_sb(struct file_
init_container_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, container_test_super, container_set_super, root);

@@ -1125,7 +1221,7 @@ static int attach_task(struct container
ss->attach(ss, cont, oldcont, tsk);
}
}
-
+ set_bit(CONT_RELEASABLE, &oldcont->flags);
synchronize_rcu();
put_css_group(cg);
return 0;
@@ -1175,6 +1271,9 @@ enum container_filetype {
FILE_ROOT,
FILE_DIR,
FILE_TASKLIST,
+ FILE_NOTIFY_ON_RELEASE,
+ FILE_RELEASABLE,
+ FILE_RELEASE_AGENT,
};

static ssize_t container_common_file_write(struct container *cont,
@@ -1212,6 +1311,32 @@ static ssize_t container_common_file_wri
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 containerfs_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;
@@ -1252,6 +1377,49 @@ static ssize_t container_read_uint(struc
return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

+static ssize_t container_common_file_read(struct container *cont,
+ struct cftype *cft,
+ struct file *file,
+ char __user *buf,
+ size_t nbytes, loff_t *ppos)
+{
+ enum container_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 containerfs_root *root;
+ size_t n;
+ mutex_lock(&container_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(&container_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 container_file_read(struct file *file, char __user *buf,
size_t nbytes, loff_t *ppos)
{
@@ -1667,16 +1835,49 @@ static int container_tasks_release(struc
return 0;
}

+static u64 container_read_notify_on_release(struct container *cont,
+ struct cftype *cft)
+{
+ return notify_on_release(cont);
+}
+
+static u64 container_read_releasable(struct container *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 = container_tasks_open,
- .read = container_tasks_read,
+static struct cftype files[] = {
+ {
+ .name = "tasks",
+ .open = container_tasks_open,
+ .read = container_tasks_read,
+ .write = container_common_file_write,
+ .release = container_tasks_release,
+ .private = FILE_TASKLIST,
+ },
+
+ {
+ .name = "notify_on_release",
+ .read_uint = container_read_notify_on_release,
+ .write = container_common_file_write,
+ .private = FILE_NOTIFY_ON_RELEASE,
+ },
+
+ {
+ .name = "releasable",
+ .read_uint = container_read_releasable,
+ .private = FILE_RELEASABLE,
+ }
+};
+
+static struct cftype cft_release_agent = {
+ .name = "release_agent",
+ .read = container_common_file_read,
.write = container_common_file_write,
- .release = container_tasks_release,
- .private = FILE_TASKLIST,
+ .private = FILE_RELEASE_AGENT,
};

static int container_populate_dir(struct container *cont)
@@ -1687,10 +1888,15 @@ static int container_populate_dir(struct
/* First clear out any existing files */
container_clear_directory(cont->dentry);

- err = container_add_file(cont, NULL, &cft_tasks);
+ err = container_add_files(cont, NULL, files, ARRAY_SIZE(files));
if (err < 0)
return err;

+ if (cont == cont->top_container) {
+ if ((err = container_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;
@@ -1747,6 +1953,7 @@ static long container_create(struct cont
INIT_LIST_HEAD(&cont->sibling);
INIT_LIST_HEAD(&cont->children);
INIT_LIST_HEAD(&cont->css_groups);
+ INIT_LIST_HEAD(&cont->release_list);

cont->parent = parent;
cont->root = parent->root;
@@ -1808,6 +2015,38 @@ static int container_mkdir(struct inode
return container_create(c_parent, dentry, mode | S_IFDIR);
}

+static inline int container_has_css_refs(struct container *cont)
+{
+ /* Check the reference count on each subsystem. Since we
+ * already established that there are no tasks in the
+ * container, 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 < CONTAINER_SUBSYS_COUNT; i++) {
+ struct container_subsys *ss = subsys[i];
+ struct container_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 container has been removed
+ * and the css deleted. But a false-positive doesn't
+ * matter, since it can only happen if the container
+ * 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 container_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
struct container *cont = dentry->d_fsdata;
@@ -1816,7 +2055,6 @@ static int container_rmdir(struct inode
struct container_subsys *ss;
struct super_block *sb;
struct containerfs_root *root;
- int css_busy = 0;

/* the vfs holds both inode->i_mutex already */

@@ -1834,20 +2072,7 @@ static int container_rmdir(struct inode
root = cont->root;
sb = root->sb;

- /* Check the reference count on each subsystem. Since we
- * already established that there are no tasks in the
- * container, 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 container_subsys_state *css;
- css = cont->subsys[ss->subsys_id];
- if (atomic_read(&css->refcnt)) {
- css_busy = 1;
- break;
- }
- }
- if (css_busy) {
+ if (container_has_css_refs(cont)) {
mutex_unlock(&container_mutex);
return -EBUSY;
}
@@ -1857,7 +2082,11 @@ static int container_rmdir(struct inode
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);
@@ -1869,6 +2098,9 @@ static int container_rmdir(struct inode
dput(d);
root->number_of_containers--;

+ set_bit(CONT_RELEASABLE, &parent->flags);
+ check_for_release(parent);
+
mutex_unlock(&container_mutex);
/* Drop the active superblock reference that we took when we
* created the container */
@@ -1906,15 +2138,15 @@ static void container_init_subsys(struct
/* 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;
+ 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);
- }
+ 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;

@@ -2241,7 +2473,7 @@ void container_exit(struct task_struct *
tsk->containers = &init_css_group;
task_unlock(tsk);
if (cg)
- put_css_group(cg);
+ put_css_group_taskexit(cg);
}

/**
@@ -2352,7 +2584,10 @@ int container_clone(struct task_struct *

out_release:
mutex_unlock(&inode->i_mutex);
+
+ mutex_lock(&container_mutex);
put_css_group(cg);
+ mutex_unlock(&container_mutex);
deactivate_super(parent->root->sb);
return ret;
}
@@ -2382,3 +2617,111 @@ int container_is_descendant(const struct
ret = (cont == target);
return ret;
}
+
+static void check_for_release(struct container *cont)
+{
+ /* All of these checks rely on RCU to keep the container
+ * structure alive */
+ if (container_is_releasable(cont) && !atomic_read(&cont->count)
+ && list_empty(&cont->children) && !container_has_css_refs(cont)) {
+ /* Container 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 (!container_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 container_subsys_state *css)
+{
+ struct container *cont = css->container;
+ 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 container is released, by running the
+ * configured release agent with the name of the container (path
+ * relative to the root of container file system) as the argument.
+ *
+ * Most likely, this user command will try to rmdir this container.
+ *
+ * This races with the possibility that some other task will be
+ * attached to this container before it is removed, or that some other
+ * user task will 'mkdir' a child container of this container. That's ok.
+ * The presumed 'rmdir' will fail quietly if this container is no longer
+ * unused, and this container 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 container_release_agent(struct work_struct *work)
+{
+ BUG_ON(work != &release_agent_work);
+ mutex_lock(&container_mutex);
+ spin_lock(&release_list_lock);
+ while (!list_empty(&release_list)) {
+ char *argv[3], *envp[3];
+ int i;
+ char *pathbuf;
+ struct container *cont = list_entry(release_list.next,
+ struct container,
+ 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 (container_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(&container_mutex);
+ call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+ kfree(pathbuf);
+ mutex_lock(&container_mutex);
+ spin_lock(&release_list_lock);
+ }
+ spin_unlock(&release_list_lock);
+ mutex_unlock(&container_mutex);
+}

--