Commit 74a1166d authored by Ben Blum's avatar Ben Blum Committed by Linus Torvalds

cgroups: make procs file writable

Make procs file writable to move all threads by tgid at once.

Add functionality that enables users to move all threads in a threadgroup
at once to a cgroup by writing the tgid to the 'cgroup.procs' file.  This
current implementation makes use of a per-threadgroup rwsem that's taken
for reading in the fork() path to prevent newly forking threads within the
threadgroup from "escaping" while the move is in progress.
Signed-off-by: default avatarBen Blum <bblum@andrew.cmu.edu>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Reviewed-by: default avatarPaul Menage <menage@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f780bdb7
......@@ -236,7 +236,8 @@ containing the following files describing that cgroup:
- cgroup.procs: list of tgids in the cgroup. This list is not
guaranteed to be sorted or free of duplicate tgids, and userspace
should sort/uniquify the list if this property is required.
This is a read-only file, for now.
Writing a thread group id into this file moves all threads in that
group into this cgroup.
- notify_on_release flag: run the release agent on exit?
- release_agent: the path to use for release notifications (this file
exists in the top cgroup only)
......@@ -430,6 +431,12 @@ You can attach the current shell task by echoing 0:
# echo 0 > tasks
You can use the cgroup.procs file instead of the tasks file to move all
threads in a threadgroup at once. Echoing the pid of any task in a
threadgroup to cgroup.procs causes all tasks in that threadgroup to be
be attached to the cgroup. Writing 0 to cgroup.procs moves all tasks
in the writing task's threadgroup.
Note: Since every task is always a member of exactly one cgroup in each
mounted hierarchy, to remove a task from its current cgroup you must
move it into a new cgroup (possibly the root cgroup) by writing to the
......
......@@ -1735,6 +1735,76 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
}
EXPORT_SYMBOL_GPL(cgroup_path);
/*
* cgroup_task_migrate - move a task from one cgroup to another.
*
* 'guarantee' is set if the caller promises that a new css_set for the task
* will already exist. If not set, this function might sleep, and can fail with
* -ENOMEM. Otherwise, it can only fail with -ESRCH.
*/
static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
struct task_struct *tsk, bool guarantee)
{
struct css_set *oldcg;
struct css_set *newcg;
/*
* get old css_set. we need to take task_lock and refcount it, because
* an exiting task can change its css_set to init_css_set and drop its
* old one without taking cgroup_mutex.
*/
task_lock(tsk);
oldcg = tsk->cgroups;
get_css_set(oldcg);
task_unlock(tsk);
/* locate or allocate a new css_set for this task. */
if (guarantee) {
/* we know the css_set we want already exists. */
struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
read_lock(&css_set_lock);
newcg = find_existing_css_set(oldcg, cgrp, template);
BUG_ON(!newcg);
get_css_set(newcg);
read_unlock(&css_set_lock);
} else {
might_sleep();
/* find_css_set will give us newcg already referenced. */
newcg = find_css_set(oldcg, cgrp);
if (!newcg) {
put_css_set(oldcg);
return -ENOMEM;
}
}
put_css_set(oldcg);
/* if PF_EXITING is set, the tsk->cgroups pointer is no longer safe. */
task_lock(tsk);
if (tsk->flags & PF_EXITING) {
task_unlock(tsk);
put_css_set(newcg);
return -ESRCH;
}
rcu_assign_pointer(tsk->cgroups, newcg);
task_unlock(tsk);
/* Update the css_set linked lists if we're using them */
write_lock(&css_set_lock);
if (!list_empty(&tsk->cg_list))
list_move(&tsk->cg_list, &newcg->tasks);
write_unlock(&css_set_lock);
/*
* We just gained a reference on oldcg by taking it from the task. As
* trading it for newcg is protected by cgroup_mutex, we're safe to drop
* it here; it will be freed under RCU.
*/
put_css_set(oldcg);
set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
return 0;
}
/**
* cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
* @cgrp: the cgroup the task is attaching to
......@@ -1745,11 +1815,9 @@ EXPORT_SYMBOL_GPL(cgroup_path);
*/
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
int retval = 0;
int retval;
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
struct css_set *cg;
struct css_set *newcg;
struct cgroupfs_root *root = cgrp->root;
/* Nothing to do if the task is already in that cgroup */
......@@ -1780,36 +1848,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
}
}
task_lock(tsk);
cg = tsk->cgroups;
get_css_set(cg);
task_unlock(tsk);
/*
* Locate or allocate a new css_set for this task,
* based on its final set of cgroups
*/
newcg = find_css_set(cg, cgrp);
put_css_set(cg);
if (!newcg) {
retval = -ENOMEM;
goto out;
}
task_lock(tsk);
if (tsk->flags & PF_EXITING) {
task_unlock(tsk);
put_css_set(newcg);
retval = -ESRCH;
retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
if (retval)
goto out;
}
rcu_assign_pointer(tsk->cgroups, newcg);
task_unlock(tsk);
/* Update the css_set linked lists if we're using them */
write_lock(&css_set_lock);
if (!list_empty(&tsk->cg_list))
list_move(&tsk->cg_list, &newcg->tasks);
write_unlock(&css_set_lock);
for_each_subsys(root, ss) {
if (ss->pre_attach)
......@@ -1819,9 +1860,8 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
if (ss->attach)
ss->attach(ss, cgrp, oldcgrp, tsk);
}
set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
synchronize_rcu();
put_css_set(cg);
/*
* wake up rmdir() waiter. the rmdir should fail since the cgroup
......@@ -1871,49 +1911,356 @@ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk)
EXPORT_SYMBOL_GPL(cgroup_attach_task_all);
/*
* Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
* held. May take task_lock of task
* cgroup_attach_proc works in two stages, the first of which prefetches all
* new css_sets needed (to make sure we have enough memory before committing
* to the move) and stores them in a list of entries of the following type.
* TODO: possible optimization: use css_set->rcu_head for chaining instead
*/
struct cg_list_entry {
struct css_set *cg;
struct list_head links;
};
static bool css_set_check_fetched(struct cgroup *cgrp,
struct task_struct *tsk, struct css_set *cg,
struct list_head *newcg_list)
{
struct css_set *newcg;
struct cg_list_entry *cg_entry;
struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
read_lock(&css_set_lock);
newcg = find_existing_css_set(cg, cgrp, template);
if (newcg)
get_css_set(newcg);
read_unlock(&css_set_lock);
/* doesn't exist at all? */
if (!newcg)
return false;
/* see if it's already in the list */
list_for_each_entry(cg_entry, newcg_list, links) {
if (cg_entry->cg == newcg) {
put_css_set(newcg);
return true;
}
}
/* not found */
put_css_set(newcg);
return false;
}
/*
* Find the new css_set and store it in the list in preparation for moving the
* given task to the given cgroup. Returns 0 or -ENOMEM.
*/
static int css_set_prefetch(struct cgroup *cgrp, struct css_set *cg,
struct list_head *newcg_list)
{
struct css_set *newcg;
struct cg_list_entry *cg_entry;
/* ensure a new css_set will exist for this thread */
newcg = find_css_set(cg, cgrp);
if (!newcg)
return -ENOMEM;
/* add it to the list */
cg_entry = kmalloc(sizeof(struct cg_list_entry), GFP_KERNEL);
if (!cg_entry) {
put_css_set(newcg);
return -ENOMEM;
}
cg_entry->cg = newcg;
list_add(&cg_entry->links, newcg_list);
return 0;
}
/**
* cgroup_attach_proc - attach all threads in a threadgroup to a cgroup
* @cgrp: the cgroup to attach to
* @leader: the threadgroup leader task_struct of the group to be attached
*
* Call holding cgroup_mutex and the threadgroup_fork_lock of the leader. Will
* take task_lock of each thread in leader's threadgroup individually in turn.
*/
int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
{
int retval, i, group_size;
struct cgroup_subsys *ss, *failed_ss = NULL;
bool cancel_failed_ss = false;
/* guaranteed to be initialized later, but the compiler needs this */
struct cgroup *oldcgrp = NULL;
struct css_set *oldcg;
struct cgroupfs_root *root = cgrp->root;
/* threadgroup list cursor and array */
struct task_struct *tsk;
struct task_struct **group;
/*
* we need to make sure we have css_sets for all the tasks we're
* going to move -before- we actually start moving them, so that in
* case we get an ENOMEM we can bail out before making any changes.
*/
struct list_head newcg_list;
struct cg_list_entry *cg_entry, *temp_nobe;
/*
* step 0: in order to do expensive, possibly blocking operations for
* every thread, we cannot iterate the thread group list, since it needs
* rcu or tasklist locked. instead, build an array of all threads in the
* group - threadgroup_fork_lock prevents new threads from appearing,
* and if threads exit, this will just be an over-estimate.
*/
group_size = get_nr_threads(leader);
group = kmalloc(group_size * sizeof(*group), GFP_KERNEL);
if (!group)
return -ENOMEM;
/* prevent changes to the threadgroup list while we take a snapshot. */
rcu_read_lock();
if (!thread_group_leader(leader)) {
/*
* a race with de_thread from another thread's exec() may strip
* us of our leadership, making while_each_thread unsafe to use
* on this task. if this happens, there is no choice but to
* throw this task away and try again (from cgroup_procs_write);
* this is "double-double-toil-and-trouble-check locking".
*/
rcu_read_unlock();
retval = -EAGAIN;
goto out_free_group_list;
}
/* take a reference on each task in the group to go in the array. */
tsk = leader;
i = 0;
do {
/* as per above, nr_threads may decrease, but not increase. */
BUG_ON(i >= group_size);
get_task_struct(tsk);
group[i] = tsk;
i++;
} while_each_thread(leader, tsk);
/* remember the number of threads in the array for later. */
group_size = i;
rcu_read_unlock();
/*
* step 1: check that we can legitimately attach to the cgroup.
*/
for_each_subsys(root, ss) {
if (ss->can_attach) {
retval = ss->can_attach(ss, cgrp, leader);
if (retval) {
failed_ss = ss;
goto out_cancel_attach;
}
}
/* a callback to be run on every thread in the threadgroup. */
if (ss->can_attach_task) {
/* run on each task in the threadgroup. */
for (i = 0; i < group_size; i++) {
retval = ss->can_attach_task(cgrp, group[i]);
if (retval) {
failed_ss = ss;
cancel_failed_ss = true;
goto out_cancel_attach;
}
}
}
}
/*
* step 2: make sure css_sets exist for all threads to be migrated.
* we use find_css_set, which allocates a new one if necessary.
*/
INIT_LIST_HEAD(&newcg_list);
for (i = 0; i < group_size; i++) {
tsk = group[i];
/* nothing to do if this task is already in the cgroup */
oldcgrp = task_cgroup_from_root(tsk, root);
if (cgrp == oldcgrp)
continue;
/* get old css_set pointer */
task_lock(tsk);
if (tsk->flags & PF_EXITING) {
/* ignore this task if it's going away */
task_unlock(tsk);
continue;
}
oldcg = tsk->cgroups;
get_css_set(oldcg);
task_unlock(tsk);
/* see if the new one for us is already in the list? */
if (css_set_check_fetched(cgrp, tsk, oldcg, &newcg_list)) {
/* was already there, nothing to do. */
put_css_set(oldcg);
} else {
/* we don't already have it. get new one. */
retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
put_css_set(oldcg);
if (retval)
goto out_list_teardown;
}
}
/*
* step 3: now that we're guaranteed success wrt the css_sets, proceed
* to move all tasks to the new cgroup, calling ss->attach_task for each
* one along the way. there are no failure cases after here, so this is
* the commit point.
*/
for_each_subsys(root, ss) {
if (ss->pre_attach)
ss->pre_attach(cgrp);
}
for (i = 0; i < group_size; i++) {
tsk = group[i];
/* leave current thread as it is if it's already there */
oldcgrp = task_cgroup_from_root(tsk, root);
if (cgrp == oldcgrp)
continue;
/* attach each task to each subsystem */
for_each_subsys(root, ss) {
if (ss->attach_task)
ss->attach_task(cgrp, tsk);
}
/* if the thread is PF_EXITING, it can just get skipped. */
retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
BUG_ON(retval != 0 && retval != -ESRCH);
}
/* nothing is sensitive to fork() after this point. */
/*
* step 4: do expensive, non-thread-specific subsystem callbacks.
* TODO: if ever a subsystem needs to know the oldcgrp for each task
* being moved, this call will need to be reworked to communicate that.
*/
for_each_subsys(root, ss) {
if (ss->attach)
ss->attach(ss, cgrp, oldcgrp, leader);
}
/*
* step 5: success! and cleanup
*/
synchronize_rcu();
cgroup_wakeup_rmdir_waiter(cgrp);
retval = 0;
out_list_teardown:
/* clean up the list of prefetched css_sets. */
list_for_each_entry_safe(cg_entry, temp_nobe, &newcg_list, links) {
list_del(&cg_entry->links);
put_css_set(cg_entry->cg);
kfree(cg_entry);
}
out_cancel_attach:
/* same deal as in cgroup_attach_task */
if (retval) {
for_each_subsys(root, ss) {
if (ss == failed_ss) {
if (cancel_failed_ss && ss->cancel_attach)
ss->cancel_attach(ss, cgrp, leader);
break;
}
if (ss->cancel_attach)
ss->cancel_attach(ss, cgrp, leader);
}
}
/* clean up the array of referenced threads in the group. */
for (i = 0; i < group_size; i++)
put_task_struct(group[i]);
out_free_group_list:
kfree(group);
return retval;
}
/*
* Find the task_struct of the task to attach by vpid and pass it along to the
* function to attach either it or all tasks in its threadgroup. Will take
* cgroup_mutex; may take task_lock of task.
*/
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
{
struct task_struct *tsk;
const struct cred *cred = current_cred(), *tcred;
int ret;
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;
if (pid) {
rcu_read_lock();
tsk = find_task_by_vpid(pid);
if (!tsk || tsk->flags & PF_EXITING) {
if (!tsk) {
rcu_read_unlock();
cgroup_unlock();
return -ESRCH;
}
if (threadgroup) {
/*
* RCU protects this access, since tsk was found in the
* tid map. a race with de_thread may cause group_leader
* to stop being the leader, but cgroup_attach_proc will
* detect it later.
*/
tsk = tsk->group_leader;
} else if (tsk->flags & PF_EXITING) {
/* optimization for the single-task-only case */
rcu_read_unlock();
cgroup_unlock();
return -ESRCH;
}
/*
* even if we're attaching all tasks in the thread group, we
* only need to check permissions on one of them.
*/
tcred = __task_cred(tsk);
if (cred->euid &&
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
rcu_read_unlock();
cgroup_unlock();
return -EACCES;
}
get_task_struct(tsk);
rcu_read_unlock();
} else {
tsk = current;
if (threadgroup)
tsk = current->group_leader;
else
tsk = current;
get_task_struct(tsk);
}
ret = cgroup_attach_task(cgrp, tsk);
if (threadgroup) {
threadgroup_fork_write_lock(tsk);
ret = cgroup_attach_proc(cgrp, tsk);
threadgroup_fork_write_unlock(tsk);
} else {
ret = cgroup_attach_task(cgrp, tsk);
}
put_task_struct(tsk);
cgroup_unlock();
return ret;
}
static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
{
return attach_task_by_pid(cgrp, pid, false);
}
static int cgroup_procs_write(struct cgroup *cgrp, struct cftype *cft, u64 tgid)
{
int ret;
if (!cgroup_lock_live_group(cgrp))
return -ENODEV;
ret = attach_task_by_pid(cgrp, pid);
cgroup_unlock();
do {
/*
* attach_proc fails with -EAGAIN if threadgroup leadership
* changes in the middle of the operation, in which case we need
* to find the task_struct for the new leader and start over.
*/
ret = attach_task_by_pid(cgrp, tgid, true);
} while (ret == -EAGAIN);
return ret;
}
......@@ -3270,9 +3617,9 @@ static struct cftype files[] = {
{
.name = CGROUP_FILE_GENERIC_PREFIX "procs",
.open = cgroup_procs_open,
/* .write_u64 = cgroup_procs_write, TODO */
.write_u64 = cgroup_procs_write,
.release = cgroup_pidlist_release,
.mode = S_IRUGO,
.mode = S_IRUGO | S_IWUSR,
},
{
.name = "notify_on_release",
......
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