// SPDX-License-Identifier: GPL-2.0
#include <linux/cgroup.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/signal.h>
#include "cgroup-internal.h"
#include <trace/events/cgroup.h>
/*
* Propagate the cgroup frozen state upwards by the cgroup tree.
*/
static void cgroup_propagate_frozen(struct cgroup *cgrp, bool frozen)
{
int desc = 1;
/*
* If the new state is frozen, some freezing ancestor cgroups may change
* their state too, depending on if all their descendants are frozen.
*
* Otherwise, all ancestor cgroups are forced into the non-frozen state.
*/
while ((cgrp = cgroup_parent(cgrp))) {
if (frozen) {
cgrp->freezer.nr_frozen_descendants += desc;
if (!test_bit(CGRP_FROZEN, &cgrp->flags) &&
test_bit(CGRP_FREEZE, &cgrp->flags) &&
cgrp->freezer.nr_frozen_descendants ==
cgrp->nr_descendants) {
set_bit(CGRP_FROZEN, &cgrp->flags);
cgroup_file_notify(&cgrp->events_file);
TRACE_CGROUP_PATH(notify_frozen, cgrp, 1);
desc++;
}
} else {
cgrp->freezer.nr_frozen_descendants -= desc;
if (test_bit(CGRP_FROZEN, &cgrp->flags)) {
clear_bit(CGRP_FROZEN, &cgrp->flags);
cgroup_file_notify(&cgrp->events_file);
TRACE_CGROUP_PATH(notify_frozen, cgrp, 0);
desc++;
}
}
}
}
/*
* Revisit the cgroup frozen state.
* Checks if the cgroup is really frozen and perform all state transitions.
*/
void cgroup_update_frozen(struct cgroup *cgrp)
{
bool frozen;
lockdep_assert_held(&css_set_lock);
/*
* If the cgroup has to be frozen (CGRP_FREEZE bit set),
* and all tasks are frozen and/or stopped, let's consider
* the cgroup frozen. Otherwise it's not frozen.
*/
frozen = test_bit(CGRP_FREEZE, &cgrp->flags) &&
cgrp->freezer.nr_frozen_tasks == __cgroup_task_count(cgrp);
if (frozen) {
/* Already there? */
if (test_bit(CGRP_FROZEN, &cgrp->flags))
return;
set_bit(CGRP_FROZEN, &cgrp->flags);
} else {
/* Already there? */
if (!test_bit(CGRP_FROZEN, &cgrp->flags))
return;
clear_bit(CGRP_FROZEN, &cgrp->flags);
}
cgroup_file_notify(&cgrp->events_file);
TRACE_CGROUP_PATH(notify_frozen, cgrp, frozen);
/* Update the state of ancestor cgroups. */
cgroup_propagate_frozen(cgrp, frozen);
}
/*
* Increment cgroup's nr_frozen_tasks.
*/
static void cgroup_inc_frozen_cnt(struct cgroup *cgrp)
{
cgrp->freezer.nr_frozen_tasks++;
}
/*
* Decrement cgroup's nr_frozen_tasks.
*/
static void cgroup_dec_frozen_cnt(struct cgroup *cgrp)
{
cgrp->freezer.nr_frozen_tasks--;
WARN_ON_ONCE(cgrp->freezer.nr_frozen_tasks < 0);
}
/*
* Enter frozen/stopped state, if not yet there. Update cgroup's counters,
* and revisit the state of the cgroup, if necessary.
*/
void cgroup_enter_frozen(void)
{
struct cgroup *cgrp;
if (current->frozen)
return;
spin_lock_irq(&css_set_lock);
current->frozen = true;
cgrp = task_dfl_cgroup(current);
cgroup_inc_frozen_cnt(cgrp);
cgroup_update_frozen(cgrp);
spin_unlock_irq(&css_set_lock);
}
/*
* Conditionally leave frozen/stopped state. Update cgroup's counters,
* and revisit the state of the cgroup, if necessary.
*
* If always_leave is not set, and the cgroup is freezing,
* we're racing with the cgroup freezing. In this case, we don't
* drop the frozen counter to avoid a transient switch to
* the unfrozen state.
*/
void cgroup_leave_frozen(bool always_leave)
{
struct cgroup *cgrp;
spin_lock_irq(&css_set_lock);
cgrp = task_dfl_cgroup(current);
if (always_leave || !test_bit(CGRP_FREEZE, &cgrp->flags)) {
cgroup_dec_frozen_cnt(cgrp);
cgroup_update_frozen(cgrp);
WARN_ON_ONCE(!current->frozen);
current->frozen = false;
} else if (!(current->jobctl & JOBCTL_TRAP_FREEZE)) {
spin_lock(¤t->sighand->siglock);
current->jobctl |= JOBCTL_TRAP_FREEZE;
set_thread_flag(TIF_SIGPENDING);
spin_unlock(¤t->sighand->siglock);
}
spin_unlock_irq(&css_set_lock);
}
/*
* Freeze or unfreeze the task by setting or clearing the JOBCTL_TRAP_FREEZE
* jobctl bit.
*/
static void cgroup_freeze_task(struct task_struct *task, bool freeze)
{
unsigned long flags;
/* If the task is about to die, don't bother with freezing it. */
if (!lock_task_sighand(task, &flags))
return;
if (freeze) {
task->jobctl |= JOBCTL_TRAP_FREEZE;
signal_wake_up(task, false);
} else {
task->jobctl &= ~JOBCTL_TRAP_FREEZE;
wake_up_process(task);
}
unlock_task_sighand(task, &flags);
}
/*
* Freeze or unfreeze all tasks in the given cgroup.
*/
static void cgroup_do_freeze(struct cgroup *cgrp, bool freeze)
{
struct css_task_iter it;
struct task_struct *task;
lockdep_assert_held(&cgroup_mutex);
spin_lock_irq(&css_set_lock);
if (freeze)
set_bit(CGRP_FREEZE, &cgrp->flags);
else
clear_bit(CGRP_FREEZE, &cgrp->flags);
spin_unlock_irq(&css_set_lock);
if (freeze)
TRACE_CGROUP_PATH(freeze, cgrp);
else
TRACE_CGROUP_PATH(unfreeze, cgrp);
css_task_iter_start(&cgrp->self, 0, &it);
while ((task = css_task_iter_next(&it))) {
/*
* Ignore kernel threads here. Freezing cgroups containing
* kthreads isn't supported.
*/
if (task->flags & PF_KTHREAD)
continue;
cgroup_freeze_task(task, freeze);
}
css_task_iter_end(&it);
/*
* Cgroup state should be revisited here to cover empty leaf cgroups
* and cgroups which descendants are already in the desired state.
*/
spin_lock_irq(&css_set_lock);
if (cgrp->nr_descendants == cgrp->freezer.nr_frozen_descendants)
cgroup_update_frozen(cgrp);
spin_unlock_irq(&css_set_lock);
}
/*
* Adjust the task state (freeze or unfreeze) and revisit the state of
* source and destination cgroups.
*/
void cgroup_freezer_migrate_task(struct task_struct *task,
struct cgroup *src, struct cgroup *dst)
{
lockdep_assert_held(&css_set_lock);
/*
* Kernel threads are not supposed to be frozen at all.
*/
if (task->flags & PF_KTHREAD)
return;
/*
* It's not necessary to do changes if both of the src and dst cgroups
* are not freezing and task is not frozen.
*/
if (!test_bit(CGRP_FREEZE, &src->flags) &&
!test_bit(CGRP_FREEZE, &dst->flags) &&
!task->frozen)
return;
/*
* Adjust counters of freezing and frozen tasks.
* Note, that if the task is frozen, but the destination cgroup is not
* frozen, we bump both counters to keep them balanced.
*/
if (task->frozen) {
cgroup_inc_frozen_cnt(dst);
cgroup_dec_frozen_cnt(src);
}
cgroup_update_frozen(dst);
cgroup_update_frozen(src);
/*
* Force the task to the desired state.
*/
cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));
}
void cgroup_freeze(struct cgroup *cgrp, bool freeze)
{
struct cgroup_subsys_state *css;
struct cgroup *dsct;
bool applied = false;
lockdep_assert_held(&cgroup_mutex);
/*
* Nothing changed? Just exit.
*/
if (cgrp->freezer.freeze == freeze)
return;
cgrp->freezer.freeze = freeze;
/*
* Propagate changes downwards the cgroup tree.
*/
css_for_each_descendant_pre(css, &cgrp->self) {
dsct = css->cgroup;
if (cgroup_is_dead(dsct))
continue;
if (freeze) {
dsct->freezer.e_freeze++;
/*
* Already frozen because of ancestor's settings?
*/
if (dsct->freezer.e_freeze > 1)
continue;
} else {
dsct->freezer.e_freeze--;
/*
* Still frozen because of ancestor's settings?
*/
if (dsct->freezer.e_freeze > 0)
continue;
WARN_ON_ONCE(dsct->freezer.e_freeze < 0);
}
/*
* Do change actual state: freeze or unfreeze.
*/
cgroup_do_freeze(dsct, freeze);
applied = true;
}
/*
* Even if the actual state hasn't changed, let's notify a user.
* The state can be enforced by an ancestor cgroup: the cgroup
* can already be in the desired state or it can be locked in the
* opposite state, so that the transition will never happen.
* In both cases it's better to notify a user, that there is
* nothing to wait for.
*/
if (!applied) {
TRACE_CGROUP_PATH(notify_frozen, cgrp,
test_bit(CGRP_FROZEN, &cgrp->flags));
cgroup_file_notify(&cgrp->events_file);
}
}
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