mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-06 02:50:43 +00:00
![Peter Zijlstra](/assets/img/avatar_default.png)
Rewrite the core freezer to behave better wrt thawing and be simpler in general. By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is ensured frozen tasks stay frozen until thawed and don't randomly wake up early, as is currently possible. As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up two PF_flags (yay!). Specifically; the current scheme works a little like: freezer_do_not_count(); schedule(); freezer_count(); And either the task is blocked, or it lands in try_to_freezer() through freezer_count(). Now, when it is blocked, the freezer considers it frozen and continues. However, on thawing, once pm_freezing is cleared, freezer_count() stops working, and any random/spurious wakeup will let a task run before its time. That is, thawing tries to thaw things in explicit order; kernel threads and workqueues before doing bringing SMP back before userspace etc.. However due to the above mentioned races it is entirely possible for userspace tasks to thaw (by accident) before SMP is back. This can be a fatal problem in asymmetric ISA architectures (eg ARMv9) where the userspace task requires a special CPU to run. As said; replace this with a special task state TASK_FROZEN and add the following state transitions: TASK_FREEZABLE -> TASK_FROZEN __TASK_STOPPED -> TASK_FROZEN __TASK_TRACED -> TASK_FROZEN The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL (IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state is already required to deal with spurious wakeups and the freezer causes one such when thawing the task (since the original state is lost). The special __TASK_{STOPPED,TRACED} states *can* be restored since their canonical state is in ->jobctl. With this, frozen tasks need an explicit TASK_FROZEN wakeup and are free of undue (early / spurious) wakeups. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
474 lines
12 KiB
C
474 lines
12 KiB
C
/*
|
|
* 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;
|
|
}
|
|
|
|
static inline struct freezer *task_freezer(struct task_struct *task)
|
|
{
|
|
return css_freezer(task_css(task, freezer_cgrp_id));
|
|
}
|
|
|
|
static struct freezer *parent_freezer(struct freezer *freezer)
|
|
{
|
|
return css_freezer(freezer->css.parent);
|
|
}
|
|
|
|
bool cgroup_freezing(struct task_struct *task)
|
|
{
|
|
bool ret;
|
|
|
|
rcu_read_lock();
|
|
ret = task_freezer(task)->state & CGROUP_FREEZING;
|
|
rcu_read_unlock();
|
|
|
|
return ret;
|
|
}
|
|
|
|
static const char *freezer_state_strs(unsigned int state)
|
|
{
|
|
if (state & CGROUP_FROZEN)
|
|
return "FROZEN";
|
|
if (state & CGROUP_FREEZING)
|
|
return "FREEZING";
|
|
return "THAWED";
|
|
};
|
|
|
|
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;
|
|
}
|
|
|
|
/**
|
|
* 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;
|
|
static_branch_inc(&freezer_active);
|
|
}
|
|
|
|
mutex_unlock(&freezer_mutex);
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* 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)
|
|
static_branch_dec(&freezer_active);
|
|
|
|
freezer->state = 0;
|
|
|
|
mutex_unlock(&freezer_mutex);
|
|
}
|
|
|
|
static void freezer_css_free(struct cgroup_subsys_state *css)
|
|
{
|
|
kfree(css_freezer(css));
|
|
}
|
|
|
|
/*
|
|
* 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);
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
}
|
|
|
|
/**
|
|
* 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) && !frozen(task))
|
|
goto out_iter_end;
|
|
}
|
|
|
|
freezer->state |= CGROUP_FROZEN;
|
|
out_iter_end:
|
|
css_task_iter_end(&it);
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
/**
|
|
* 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))
|
|
static_branch_inc(&freezer_active);
|
|
freezer->state |= state;
|
|
freeze_cgroup(freezer);
|
|
} else {
|
|
bool was_freezing = freezer->state & CGROUP_FREEZING;
|
|
|
|
freezer->state &= ~state;
|
|
|
|
if (!(freezer->state & CGROUP_FREEZING)) {
|
|
freezer->state &= ~CGROUP_FROZEN;
|
|
if (was_freezing)
|
|
static_branch_dec(&freezer_active);
|
|
unfreeze_cgroup(freezer);
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* 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);
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
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,
|
|
};
|