cregit-Linux how code gets into the kernel

Release 4.15 kernel/cgroup/freezer.c

Directory: kernel/cgroup
/*
 * cgroup_freezer.c -  control group freezer subsystem
 *
 * Copyright IBM Corporation, 2007
 *
 * Author : Cedric Le Goater <clg@fr.ibm.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2.1 of the GNU Lesser General Public License
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <linux/export.h>
#include <linux/slab.h>
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/freezer.h>
#include <linux/seq_file.h>
#include <linux/mutex.h>

/*
 * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 * its ancestors has FREEZING_SELF set.
 */

enum freezer_state_flags {
	
CGROUP_FREEZER_ONLINE	= (1 << 0), /* freezer is fully online */
	
CGROUP_FREEZING_SELF	= (1 << 1), /* this freezer is freezing */
	
CGROUP_FREEZING_PARENT	= (1 << 2), /* the parent freezer is freezing */
	
CGROUP_FROZEN		= (1 << 3), /* this and its descendants frozen */

	/* mask for all FREEZING flags */
	
CGROUP_FREEZING		= CGROUP_FREEZING_SELF | CGROUP_FREEZING_PARENT,
};


struct freezer {
	
struct cgroup_subsys_state	css;
	
unsigned int			state;
};

static DEFINE_MUTEX(freezer_mutex);


static inline struct freezer *css_freezer(struct cgroup_subsys_state *css) { return css ? container_of(css, struct freezer, css) : NULL; }

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static inline struct freezer *task_freezer(struct task_struct *task) { return css_freezer(task_css(task, freezer_cgrp_id)); }

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static struct freezer *parent_freezer(struct freezer *freezer) { return css_freezer(freezer->css.parent); }

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bool cgroup_freezing(struct task_struct *task) { bool ret; rcu_read_lock(); ret = task_freezer(task)->state & CGROUP_FREEZING; rcu_read_unlock(); return ret; }

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static const char *freezer_state_strs(unsigned int state) { if (state & CGROUP_FROZEN) return "FROZEN"; if (state & CGROUP_FREEZING) return "FREEZING"; return "THAWED"; }

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;
static struct cgroup_subsys_state * freezer_css_alloc(struct cgroup_subsys_state *parent_css) { struct freezer *freezer; freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL); if (!freezer) return ERR_PTR(-ENOMEM); return &freezer->css; }

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/** * freezer_css_online - commit creation of a freezer css * @css: css being created * * We're committing to creation of @css. Mark it online and inherit * parent's freezing state while holding both parent's and our * freezer->lock. */
static int freezer_css_online(struct cgroup_subsys_state *css) { struct freezer *freezer = css_freezer(css); struct freezer *parent = parent_freezer(freezer); mutex_lock(&freezer_mutex); freezer->state |= CGROUP_FREEZER_ONLINE; if (parent && (parent->state & CGROUP_FREEZING)) { freezer->state |= CGROUP_FREEZING_PARENT | CGROUP_FROZEN; atomic_inc(&system_freezing_cnt); } mutex_unlock(&freezer_mutex); return 0; }

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/** * freezer_css_offline - initiate destruction of a freezer css * @css: css being destroyed * * @css is going away. Mark it dead and decrement system_freezing_count if * it was holding one. */
static void freezer_css_offline(struct cgroup_subsys_state *css) { struct freezer *freezer = css_freezer(css); mutex_lock(&freezer_mutex); if (freezer->state & CGROUP_FREEZING) atomic_dec(&system_freezing_cnt); freezer->state = 0; mutex_unlock(&freezer_mutex); }

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static void freezer_css_free(struct cgroup_subsys_state *css) { kfree(css_freezer(css)); }

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/* * Tasks can be migrated into a different freezer anytime regardless of its * current state. freezer_attach() is responsible for making new tasks * conform to the current state. * * Freezer state changes and task migration are synchronized via * @freezer->lock. freezer_attach() makes the new tasks conform to the * current state and all following state changes can see the new tasks. */
static void freezer_attach(struct cgroup_taskset *tset) { struct task_struct *task; struct cgroup_subsys_state *new_css; mutex_lock(&freezer_mutex); /* * Make the new tasks conform to the current state of @new_css. * For simplicity, when migrating any task to a FROZEN cgroup, we * revert it to FREEZING and let update_if_frozen() determine the * correct state later. * * Tasks in @tset are on @new_css but may not conform to its * current state before executing the following - !frozen tasks may * be visible in a FROZEN cgroup and frozen tasks in a THAWED one. */ cgroup_taskset_for_each(task, new_css, tset) { struct freezer *freezer = css_freezer(new_css); if (!(freezer->state & CGROUP_FREEZING)) { __thaw_task(task); } else { freeze_task(task); /* clear FROZEN and propagate upwards */ while (freezer && (freezer->state & CGROUP_FROZEN)) { freezer->state &= ~CGROUP_FROZEN; freezer = parent_freezer(freezer); } } } mutex_unlock(&freezer_mutex); }

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/** * freezer_fork - cgroup post fork callback * @task: a task which has just been forked * * @task has just been created and should conform to the current state of * the cgroup_freezer it belongs to. This function may race against * freezer_attach(). Losing to freezer_attach() means that we don't have * to do anything as freezer_attach() will put @task into the appropriate * state. */
static void freezer_fork(struct task_struct *task) { struct freezer *freezer; /* * The root cgroup is non-freezable, so we can skip locking the * freezer. This is safe regardless of race with task migration. * If we didn't race or won, skipping is obviously the right thing * to do. If we lost and root is the new cgroup, noop is still the * right thing to do. */ if (task_css_is_root(task, freezer_cgrp_id)) return; mutex_lock(&freezer_mutex); rcu_read_lock(); freezer = task_freezer(task); if (freezer->state & CGROUP_FREEZING) freeze_task(task); rcu_read_unlock(); mutex_unlock(&freezer_mutex); }

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/** * update_if_frozen - update whether a cgroup finished freezing * @css: css of interest * * Once FREEZING is initiated, transition to FROZEN is lazily updated by * calling this function. If the current state is FREEZING but not FROZEN, * this function checks whether all tasks of this cgroup and the descendant * cgroups finished freezing and, if so, sets FROZEN. * * The caller is responsible for grabbing RCU read lock and calling * update_if_frozen() on all descendants prior to invoking this function. * * Task states and freezer state might disagree while tasks are being * migrated into or out of @css, so we can't verify task states against * @freezer state here. See freezer_attach() for details. */
static void update_if_frozen(struct cgroup_subsys_state *css) { struct freezer *freezer = css_freezer(css); struct cgroup_subsys_state *pos; struct css_task_iter it; struct task_struct *task; lockdep_assert_held(&freezer_mutex); if (!(freezer->state & CGROUP_FREEZING) || (freezer->state & CGROUP_FROZEN)) return; /* are all (live) children frozen? */ rcu_read_lock(); css_for_each_child(pos, css) { struct freezer *child = css_freezer(pos); if ((child->state & CGROUP_FREEZER_ONLINE) && !(child->state & CGROUP_FROZEN)) { rcu_read_unlock(); return; } } rcu_read_unlock(); /* are all tasks frozen? */ css_task_iter_start(css, 0, &it); while ((task = css_task_iter_next(&it))) { if (freezing(task)) { /* * freezer_should_skip() indicates that the task * should be skipped when determining freezing * completion. Consider it frozen in addition to * the usual frozen condition. */ if (!frozen(task) && !freezer_should_skip(task)) goto out_iter_end; } } freezer->state |= CGROUP_FROZEN; out_iter_end: css_task_iter_end(&it); }

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static int freezer_read(struct seq_file *m, void *v) { struct cgroup_subsys_state *css = seq_css(m), *pos; mutex_lock(&freezer_mutex); rcu_read_lock(); /* update states bottom-up */ css_for_each_descendant_post(pos, css) { if (!css_tryget_online(pos)) continue; rcu_read_unlock(); update_if_frozen(pos); rcu_read_lock(); css_put(pos); } rcu_read_unlock(); mutex_unlock(&freezer_mutex); seq_puts(m, freezer_state_strs(css_freezer(css)->state)); seq_putc(m, '\n'); return 0; }

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static void freeze_cgroup(struct freezer *freezer) { struct css_task_iter it; struct task_struct *task; css_task_iter_start(&freezer->css, 0, &it); while ((task = css_task_iter_next(&it))) freeze_task(task); css_task_iter_end(&it); }

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static void unfreeze_cgroup(struct freezer *freezer) { struct css_task_iter it; struct task_struct *task; css_task_iter_start(&freezer->css, 0, &it); while ((task = css_task_iter_next(&it))) __thaw_task(task); css_task_iter_end(&it); }

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/** * freezer_apply_state - apply state change to a single cgroup_freezer * @freezer: freezer to apply state change to * @freeze: whether to freeze or unfreeze * @state: CGROUP_FREEZING_* flag to set or clear * * Set or clear @state on @cgroup according to @freeze, and perform * freezing or thawing as necessary. */
static void freezer_apply_state(struct freezer *freezer, bool freeze, unsigned int state) { /* also synchronizes against task migration, see freezer_attach() */ lockdep_assert_held(&freezer_mutex); if (!(freezer->state & CGROUP_FREEZER_ONLINE)) return; if (freeze) { if (!(freezer->state & CGROUP_FREEZING)) atomic_inc(&system_freezing_cnt); freezer->state |= state; freeze_cgroup(freezer); } else { bool was_freezing = freezer->state & CGROUP_FREEZING; freezer->state &= ~state; if (!(freezer->state & CGROUP_FREEZING)) { if (was_freezing) atomic_dec(&system_freezing_cnt); freezer->state &= ~CGROUP_FROZEN; unfreeze_cgroup(freezer); } } }

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/** * freezer_change_state - change the freezing state of a cgroup_freezer * @freezer: freezer of interest * @freeze: whether to freeze or thaw * * Freeze or thaw @freezer according to @freeze. The operations are * recursive - all descendants of @freezer will be affected. */
static void freezer_change_state(struct freezer *freezer, bool freeze) { struct cgroup_subsys_state *pos; /* * Update all its descendants in pre-order traversal. Each * descendant will try to inherit its parent's FREEZING state as * CGROUP_FREEZING_PARENT. */ mutex_lock(&freezer_mutex); rcu_read_lock(); css_for_each_descendant_pre(pos, &freezer->css) { struct freezer *pos_f = css_freezer(pos); struct freezer *parent = parent_freezer(pos_f); if (!css_tryget_online(pos)) continue; rcu_read_unlock(); if (pos_f == freezer) freezer_apply_state(pos_f, freeze, CGROUP_FREEZING_SELF); else freezer_apply_state(pos_f, parent->state & CGROUP_FREEZING, CGROUP_FREEZING_PARENT); rcu_read_lock(); css_put(pos); } rcu_read_unlock(); mutex_unlock(&freezer_mutex); }

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static ssize_t freezer_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { bool freeze; buf = strstrip(buf); if (strcmp(buf, freezer_state_strs(0)) == 0) freeze = false; else if (strcmp(buf, freezer_state_strs(CGROUP_FROZEN)) == 0) freeze = true; else return -EINVAL; freezer_change_state(css_freezer(of_css(of)), freeze); return nbytes; }

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static u64 freezer_self_freezing_read(struct cgroup_subsys_state *css, struct cftype *cft) { struct freezer *freezer = css_freezer(css); return (bool)(freezer->state & CGROUP_FREEZING_SELF); }

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static u64 freezer_parent_freezing_read(struct cgroup_subsys_state *css, struct cftype *cft) { struct freezer *freezer = css_freezer(css); return (bool)(freezer->state & CGROUP_FREEZING_PARENT); }

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static struct cftype files[] = { { .name = "state", .flags = CFTYPE_NOT_ON_ROOT, .seq_show = freezer_read, .write = freezer_write, }, { .name = "self_freezing", .flags = CFTYPE_NOT_ON_ROOT, .read_u64 = freezer_self_freezing_read, }, { .name = "parent_freezing", .flags = CFTYPE_NOT_ON_ROOT, .read_u64 = freezer_parent_freezing_read, }, { } /* terminate */ }; struct cgroup_subsys freezer_cgrp_subsys = { .css_alloc = freezer_css_alloc, .css_online = freezer_css_online, .css_offline = freezer_css_offline, .css_free = freezer_css_free, .attach = freezer_attach, .fork = freezer_fork, .legacy_cftypes = files, };

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Directory: kernel/cgroup
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