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![Aleksa Sarai](/assets/img/avatar_default.png)
Add a new cgroup subsystem callback can_fork that conditionally states whether or not the fork is accepted or rejected by a cgroup policy. In addition, add a cancel_fork callback so that if an error occurs later in the forking process, any state modified by can_fork can be reverted. Allow for a private opaque pointer to be passed from cgroup_can_fork to cgroup_post_fork, allowing for the fork state to be stored by each subsystem separately. Also add a tagging system for cgroup_subsys.h to allow for CGROUP_<TAG> enumerations to be be defined and used. In addition, explicitly add a CGROUP_CANFORK_COUNT macro to make arrays easier to define. This is in preparation for implementing the pids cgroup subsystem. Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> Signed-off-by: Tejun Heo <tj@kernel.org>
484 lines
12 KiB
C
484 lines
12 KiB
C
/*
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* cgroup_freezer.c - control group freezer subsystem
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*
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* Copyright IBM Corporation, 2007
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*
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* Author : Cedric Le Goater <clg@fr.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2.1 of the GNU Lesser General Public License
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it would be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#include <linux/export.h>
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#include <linux/slab.h>
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#include <linux/cgroup.h>
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#include <linux/fs.h>
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#include <linux/uaccess.h>
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#include <linux/freezer.h>
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#include <linux/seq_file.h>
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#include <linux/mutex.h>
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/*
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* A cgroup is freezing if any FREEZING flags are set. FREEZING_SELF is
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* set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
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* for "THAWED". FREEZING_PARENT is set if the parent freezer is FREEZING
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* for whatever reason. IOW, a cgroup has FREEZING_PARENT set if one of
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* its ancestors has FREEZING_SELF set.
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*/
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enum freezer_state_flags {
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CGROUP_FREEZER_ONLINE = (1 << 0), /* freezer is fully online */
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CGROUP_FREEZING_SELF = (1 << 1), /* this freezer is freezing */
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CGROUP_FREEZING_PARENT = (1 << 2), /* the parent freezer is freezing */
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CGROUP_FROZEN = (1 << 3), /* this and its descendants frozen */
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/* mask for all FREEZING flags */
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CGROUP_FREEZING = CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
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};
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struct freezer {
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struct cgroup_subsys_state css;
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unsigned int state;
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};
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static DEFINE_MUTEX(freezer_mutex);
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static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
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{
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return css ? container_of(css, struct freezer, css) : NULL;
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}
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static inline struct freezer *task_freezer(struct task_struct *task)
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{
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return css_freezer(task_css(task, freezer_cgrp_id));
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}
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static struct freezer *parent_freezer(struct freezer *freezer)
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{
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return css_freezer(freezer->css.parent);
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}
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bool cgroup_freezing(struct task_struct *task)
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{
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bool ret;
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rcu_read_lock();
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ret = task_freezer(task)->state & CGROUP_FREEZING;
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rcu_read_unlock();
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return ret;
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}
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static const char *freezer_state_strs(unsigned int state)
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{
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if (state & CGROUP_FROZEN)
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return "FROZEN";
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if (state & CGROUP_FREEZING)
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return "FREEZING";
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return "THAWED";
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};
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static struct cgroup_subsys_state *
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freezer_css_alloc(struct cgroup_subsys_state *parent_css)
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{
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struct freezer *freezer;
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freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
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if (!freezer)
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return ERR_PTR(-ENOMEM);
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return &freezer->css;
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}
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/**
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* freezer_css_online - commit creation of a freezer css
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* @css: css being created
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*
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* We're committing to creation of @css. Mark it online and inherit
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* parent's freezing state while holding both parent's and our
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* freezer->lock.
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*/
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static int freezer_css_online(struct cgroup_subsys_state *css)
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{
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struct freezer *freezer = css_freezer(css);
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struct freezer *parent = parent_freezer(freezer);
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mutex_lock(&freezer_mutex);
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freezer->state |= CGROUP_FREEZER_ONLINE;
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if (parent && (parent->state & CGROUP_FREEZING)) {
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freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN;
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atomic_inc(&system_freezing_cnt);
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}
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mutex_unlock(&freezer_mutex);
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return 0;
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}
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/**
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* freezer_css_offline - initiate destruction of a freezer css
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* @css: css being destroyed
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*
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* @css is going away. Mark it dead and decrement system_freezing_count if
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* it was holding one.
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*/
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static void freezer_css_offline(struct cgroup_subsys_state *css)
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{
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struct freezer *freezer = css_freezer(css);
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mutex_lock(&freezer_mutex);
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if (freezer->state & CGROUP_FREEZING)
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atomic_dec(&system_freezing_cnt);
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freezer->state = 0;
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mutex_unlock(&freezer_mutex);
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}
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static void freezer_css_free(struct cgroup_subsys_state *css)
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{
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kfree(css_freezer(css));
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}
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/*
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* Tasks can be migrated into a different freezer anytime regardless of its
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* current state. freezer_attach() is responsible for making new tasks
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* conform to the current state.
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*
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* Freezer state changes and task migration are synchronized via
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* @freezer->lock. freezer_attach() makes the new tasks conform to the
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* current state and all following state changes can see the new tasks.
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*/
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static void freezer_attach(struct cgroup_subsys_state *new_css,
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struct cgroup_taskset *tset)
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{
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struct freezer *freezer = css_freezer(new_css);
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struct task_struct *task;
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bool clear_frozen = false;
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mutex_lock(&freezer_mutex);
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/*
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* Make the new tasks conform to the current state of @new_css.
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* For simplicity, when migrating any task to a FROZEN cgroup, we
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* revert it to FREEZING and let update_if_frozen() determine the
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* correct state later.
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*
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* Tasks in @tset are on @new_css but may not conform to its
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* current state before executing the following - !frozen tasks may
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* be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
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*/
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cgroup_taskset_for_each(task, tset) {
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if (!(freezer->state & CGROUP_FREEZING)) {
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__thaw_task(task);
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} else {
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freeze_task(task);
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freezer->state &= ~CGROUP_FROZEN;
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clear_frozen = true;
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}
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}
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/* propagate FROZEN clearing upwards */
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while (clear_frozen && (freezer = parent_freezer(freezer))) {
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freezer->state &= ~CGROUP_FROZEN;
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clear_frozen = freezer->state & CGROUP_FREEZING;
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}
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mutex_unlock(&freezer_mutex);
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}
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/**
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* freezer_fork - cgroup post fork callback
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* @task: a task which has just been forked
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*
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* @task has just been created and should conform to the current state of
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* the cgroup_freezer it belongs to. This function may race against
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* freezer_attach(). Losing to freezer_attach() means that we don't have
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* to do anything as freezer_attach() will put @task into the appropriate
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* state.
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*/
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static void freezer_fork(struct task_struct *task, void *private)
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{
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struct freezer *freezer;
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/*
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* The root cgroup is non-freezable, so we can skip locking the
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* freezer. This is safe regardless of race with task migration.
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* If we didn't race or won, skipping is obviously the right thing
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* to do. If we lost and root is the new cgroup, noop is still the
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* right thing to do.
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*/
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if (task_css_is_root(task, freezer_cgrp_id))
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return;
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mutex_lock(&freezer_mutex);
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rcu_read_lock();
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freezer = task_freezer(task);
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if (freezer->state & CGROUP_FREEZING)
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freeze_task(task);
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rcu_read_unlock();
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mutex_unlock(&freezer_mutex);
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}
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/**
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* update_if_frozen - update whether a cgroup finished freezing
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* @css: css of interest
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*
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* Once FREEZING is initiated, transition to FROZEN is lazily updated by
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* calling this function. If the current state is FREEZING but not FROZEN,
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* this function checks whether all tasks of this cgroup and the descendant
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* cgroups finished freezing and, if so, sets FROZEN.
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*
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* The caller is responsible for grabbing RCU read lock and calling
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* update_if_frozen() on all descendants prior to invoking this function.
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*
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* Task states and freezer state might disagree while tasks are being
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* migrated into or out of @css, so we can't verify task states against
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* @freezer state here. See freezer_attach() for details.
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*/
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static void update_if_frozen(struct cgroup_subsys_state *css)
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{
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struct freezer *freezer = css_freezer(css);
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struct cgroup_subsys_state *pos;
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struct css_task_iter it;
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struct task_struct *task;
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lockdep_assert_held(&freezer_mutex);
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if (!(freezer->state & CGROUP_FREEZING) ||
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(freezer->state & CGROUP_FROZEN))
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return;
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/* are all (live) children frozen? */
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rcu_read_lock();
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css_for_each_child(pos, css) {
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struct freezer *child = css_freezer(pos);
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if ((child->state & CGROUP_FREEZER_ONLINE) &&
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!(child->state & CGROUP_FROZEN)) {
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rcu_read_unlock();
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return;
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}
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}
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rcu_read_unlock();
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/* are all tasks frozen? */
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css_task_iter_start(css, &it);
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while ((task = css_task_iter_next(&it))) {
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if (freezing(task)) {
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/*
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* freezer_should_skip() indicates that the task
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* should be skipped when determining freezing
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* completion. Consider it frozen in addition to
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* the usual frozen condition.
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*/
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if (!frozen(task) && !freezer_should_skip(task))
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goto out_iter_end;
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}
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}
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freezer->state |= CGROUP_FROZEN;
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out_iter_end:
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css_task_iter_end(&it);
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}
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static int freezer_read(struct seq_file *m, void *v)
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{
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struct cgroup_subsys_state *css = seq_css(m), *pos;
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mutex_lock(&freezer_mutex);
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rcu_read_lock();
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/* update states bottom-up */
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css_for_each_descendant_post(pos, css) {
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if (!css_tryget_online(pos))
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continue;
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rcu_read_unlock();
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update_if_frozen(pos);
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rcu_read_lock();
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css_put(pos);
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}
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rcu_read_unlock();
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mutex_unlock(&freezer_mutex);
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seq_puts(m, freezer_state_strs(css_freezer(css)->state));
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seq_putc(m, '\n');
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return 0;
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}
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static void freeze_cgroup(struct freezer *freezer)
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{
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struct css_task_iter it;
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struct task_struct *task;
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css_task_iter_start(&freezer->css, &it);
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while ((task = css_task_iter_next(&it)))
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freeze_task(task);
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css_task_iter_end(&it);
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}
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static void unfreeze_cgroup(struct freezer *freezer)
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{
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struct css_task_iter it;
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struct task_struct *task;
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css_task_iter_start(&freezer->css, &it);
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while ((task = css_task_iter_next(&it)))
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__thaw_task(task);
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css_task_iter_end(&it);
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}
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/**
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* freezer_apply_state - apply state change to a single cgroup_freezer
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* @freezer: freezer to apply state change to
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* @freeze: whether to freeze or unfreeze
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* @state: CGROUP_FREEZING_* flag to set or clear
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*
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* Set or clear @state on @cgroup according to @freeze, and perform
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* freezing or thawing as necessary.
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*/
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static void freezer_apply_state(struct freezer *freezer, bool freeze,
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unsigned int state)
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{
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/* also synchronizes against task migration, see freezer_attach() */
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lockdep_assert_held(&freezer_mutex);
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if (!(freezer->state & CGROUP_FREEZER_ONLINE))
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return;
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if (freeze) {
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if (!(freezer->state & CGROUP_FREEZING))
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atomic_inc(&system_freezing_cnt);
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freezer->state |= state;
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freeze_cgroup(freezer);
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} else {
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bool was_freezing = freezer->state & CGROUP_FREEZING;
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freezer->state &= ~state;
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if (!(freezer->state & CGROUP_FREEZING)) {
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if (was_freezing)
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atomic_dec(&system_freezing_cnt);
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freezer->state &= ~CGROUP_FROZEN;
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unfreeze_cgroup(freezer);
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}
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}
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}
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/**
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* freezer_change_state - change the freezing state of a cgroup_freezer
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* @freezer: freezer of interest
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* @freeze: whether to freeze or thaw
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*
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* Freeze or thaw @freezer according to @freeze. The operations are
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* recursive - all descendants of @freezer will be affected.
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*/
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static void freezer_change_state(struct freezer *freezer, bool freeze)
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{
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struct cgroup_subsys_state *pos;
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/*
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* Update all its descendants in pre-order traversal. Each
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* descendant will try to inherit its parent's FREEZING state as
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* CGROUP_FREEZING_PARENT.
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*/
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mutex_lock(&freezer_mutex);
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rcu_read_lock();
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css_for_each_descendant_pre(pos, &freezer->css) {
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struct freezer *pos_f = css_freezer(pos);
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struct freezer *parent = parent_freezer(pos_f);
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if (!css_tryget_online(pos))
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continue;
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rcu_read_unlock();
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if (pos_f == freezer)
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freezer_apply_state(pos_f, freeze,
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CGROUP_FREEZING_SELF);
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else
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freezer_apply_state(pos_f,
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parent->state & CGROUP_FREEZING,
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CGROUP_FREEZING_PARENT);
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rcu_read_lock();
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css_put(pos);
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}
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rcu_read_unlock();
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mutex_unlock(&freezer_mutex);
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}
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static ssize_t freezer_write(struct kernfs_open_file *of,
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char *buf, size_t nbytes, loff_t off)
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{
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bool freeze;
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buf = strstrip(buf);
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if (strcmp(buf, freezer_state_strs(0)) == 0)
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freeze = false;
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else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0)
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freeze = true;
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else
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return -EINVAL;
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freezer_change_state(css_freezer(of_css(of)), freeze);
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return nbytes;
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}
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static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css,
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struct cftype *cft)
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{
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struct freezer *freezer = css_freezer(css);
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return (bool)(freezer->state & CGROUP_FREEZING_SELF);
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}
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static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css,
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struct cftype *cft)
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{
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struct freezer *freezer = css_freezer(css);
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return (bool)(freezer->state & CGROUP_FREEZING_PARENT);
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}
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static struct cftype files[] = {
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{
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.name = "state",
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.flags = CFTYPE_NOT_ON_ROOT,
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.seq_show = freezer_read,
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.write = freezer_write,
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},
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{
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.name = "self_freezing",
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.flags = CFTYPE_NOT_ON_ROOT,
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.read_u64 = freezer_self_freezing_read,
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},
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{
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.name = "parent_freezing",
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.flags = CFTYPE_NOT_ON_ROOT,
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.read_u64 = freezer_parent_freezing_read,
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},
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{ } /* terminate */
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};
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struct cgroup_subsys freezer_cgrp_subsys = {
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.css_alloc = freezer_css_alloc,
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.css_online = freezer_css_online,
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.css_offline = freezer_css_offline,
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.css_free = freezer_css_free,
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.attach = freezer_attach,
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.fork = freezer_fork,
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.legacy_cftypes = files,
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};
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