kernel-ark/kernel/cgroup_freezer.c
Tejun Heo 8c7f6edbda cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them
Currently, cgroup hierarchy support is a mess.  cpu related subsystems
behave correctly - configuration, accounting and control on a parent
properly cover its children.  blkio and freezer completely ignore
hierarchy and treat all cgroups as if they're directly under the root
cgroup.  Others show yet different behaviors.

These differing interpretations of cgroup hierarchy make using cgroup
confusing and it impossible to co-mount controllers into the same
hierarchy and obtain sane behavior.

Eventually, we want full hierarchy support from all subsystems and
probably a unified hierarchy.  Users using separate hierarchies
expecting completely different behaviors depending on the mounted
subsystem is deterimental to making any progress on this front.

This patch adds cgroup_subsys.broken_hierarchy and sets it to %true
for controllers which are lacking in hierarchy support.  The goal of
this patch is two-fold.

* Move users away from using hierarchy on currently non-hierarchical
  subsystems, so that implementing proper hierarchy support on those
  doesn't surprise them.

* Keep track of which controllers are broken how and nudge the
  subsystems to implement proper hierarchy support.

For now, start with a single warning message.  We can whine louder
later on.

v2: Fixed a typo spotted by Michal. Warning message updated.

v3: Updated memcg part so that it doesn't generate warning in the
    cases where .use_hierarchy=false doesn't make the behavior
    different from root.use_hierarchy=true.  Fixed a typo spotted by
    Glauber.

v4: Check ->broken_hierarchy after cgroup creation is complete so that
    ->create() can affect the result per Michal.  Dropped unnecessary
    memcg root handling per Michal.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
2012-09-14 12:01:16 -07:00

385 lines
9.4 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>
enum freezer_state {
CGROUP_THAWED = 0,
CGROUP_FREEZING,
CGROUP_FROZEN,
};
struct freezer {
struct cgroup_subsys_state css;
enum freezer_state state;
spinlock_t lock; /* protects _writes_ to state */
};
static inline struct freezer *cgroup_freezer(
struct cgroup *cgroup)
{
return container_of(
cgroup_subsys_state(cgroup, freezer_subsys_id),
struct freezer, css);
}
static inline struct freezer *task_freezer(struct task_struct *task)
{
return container_of(task_subsys_state(task, freezer_subsys_id),
struct freezer, css);
}
bool cgroup_freezing(struct task_struct *task)
{
enum freezer_state state;
bool ret;
rcu_read_lock();
state = task_freezer(task)->state;
ret = state == CGROUP_FREEZING || state == CGROUP_FROZEN;
rcu_read_unlock();
return ret;
}
/*
* cgroups_write_string() limits the size of freezer state strings to
* CGROUP_LOCAL_BUFFER_SIZE
*/
static const char *freezer_state_strs[] = {
"THAWED",
"FREEZING",
"FROZEN",
};
/*
* State diagram
* Transitions are caused by userspace writes to the freezer.state file.
* The values in parenthesis are state labels. The rest are edge labels.
*
* (THAWED) --FROZEN--> (FREEZING) --FROZEN--> (FROZEN)
* ^ ^ | |
* | \_______THAWED_______/ |
* \__________________________THAWED____________/
*/
struct cgroup_subsys freezer_subsys;
/* Locks taken and their ordering
* ------------------------------
* cgroup_mutex (AKA cgroup_lock)
* freezer->lock
* css_set_lock
* task->alloc_lock (AKA task_lock)
* task->sighand->siglock
*
* cgroup code forces css_set_lock to be taken before task->alloc_lock
*
* freezer_create(), freezer_destroy():
* cgroup_mutex [ by cgroup core ]
*
* freezer_can_attach():
* cgroup_mutex (held by caller of can_attach)
*
* freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
* freezer->lock
* sighand->siglock (if the cgroup is freezing)
*
* freezer_read():
* cgroup_mutex
* freezer->lock
* write_lock css_set_lock (cgroup iterator start)
* task->alloc_lock
* read_lock css_set_lock (cgroup iterator start)
*
* freezer_write() (freeze):
* cgroup_mutex
* freezer->lock
* write_lock css_set_lock (cgroup iterator start)
* task->alloc_lock
* read_lock css_set_lock (cgroup iterator start)
* sighand->siglock (fake signal delivery inside freeze_task())
*
* freezer_write() (unfreeze):
* cgroup_mutex
* freezer->lock
* write_lock css_set_lock (cgroup iterator start)
* task->alloc_lock
* read_lock css_set_lock (cgroup iterator start)
* task->alloc_lock (inside __thaw_task(), prevents race with refrigerator())
* sighand->siglock
*/
static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
{
struct freezer *freezer;
freezer = kzalloc(sizeof(struct freezer), GFP_KERNEL);
if (!freezer)
return ERR_PTR(-ENOMEM);
spin_lock_init(&freezer->lock);
freezer->state = CGROUP_THAWED;
return &freezer->css;
}
static void freezer_destroy(struct cgroup *cgroup)
{
struct freezer *freezer = cgroup_freezer(cgroup);
if (freezer->state != CGROUP_THAWED)
atomic_dec(&system_freezing_cnt);
kfree(freezer);
}
/* task is frozen or will freeze immediately when next it gets woken */
static bool is_task_frozen_enough(struct task_struct *task)
{
return frozen(task) ||
(task_is_stopped_or_traced(task) && freezing(task));
}
/*
* The call to cgroup_lock() in the freezer.state write method prevents
* a write to that file racing against an attach, and hence the
* can_attach() result will remain valid until the attach completes.
*/
static int freezer_can_attach(struct cgroup *new_cgroup,
struct cgroup_taskset *tset)
{
struct freezer *freezer;
struct task_struct *task;
/*
* Anything frozen can't move or be moved to/from.
*/
cgroup_taskset_for_each(task, new_cgroup, tset)
if (cgroup_freezing(task))
return -EBUSY;
freezer = cgroup_freezer(new_cgroup);
if (freezer->state != CGROUP_THAWED)
return -EBUSY;
return 0;
}
static void freezer_fork(struct task_struct *task)
{
struct freezer *freezer;
/*
* No lock is needed, since the task isn't on tasklist yet,
* so it can't be moved to another cgroup, which means the
* freezer won't be removed and will be valid during this
* function call. Nevertheless, apply RCU read-side critical
* section to suppress RCU lockdep false positives.
*/
rcu_read_lock();
freezer = task_freezer(task);
rcu_read_unlock();
/*
* The root cgroup is non-freezable, so we can skip the
* following check.
*/
if (!freezer->css.cgroup->parent)
return;
spin_lock_irq(&freezer->lock);
BUG_ON(freezer->state == CGROUP_FROZEN);
/* Locking avoids race with FREEZING -> THAWED transitions. */
if (freezer->state == CGROUP_FREEZING)
freeze_task(task);
spin_unlock_irq(&freezer->lock);
}
/*
* caller must hold freezer->lock
*/
static void update_if_frozen(struct cgroup *cgroup,
struct freezer *freezer)
{
struct cgroup_iter it;
struct task_struct *task;
unsigned int nfrozen = 0, ntotal = 0;
enum freezer_state old_state = freezer->state;
cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it))) {
ntotal++;
if (freezing(task) && is_task_frozen_enough(task))
nfrozen++;
}
if (old_state == CGROUP_THAWED) {
BUG_ON(nfrozen > 0);
} else if (old_state == CGROUP_FREEZING) {
if (nfrozen == ntotal)
freezer->state = CGROUP_FROZEN;
} else { /* old_state == CGROUP_FROZEN */
BUG_ON(nfrozen != ntotal);
}
cgroup_iter_end(cgroup, &it);
}
static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
struct seq_file *m)
{
struct freezer *freezer;
enum freezer_state state;
if (!cgroup_lock_live_group(cgroup))
return -ENODEV;
freezer = cgroup_freezer(cgroup);
spin_lock_irq(&freezer->lock);
state = freezer->state;
if (state == CGROUP_FREEZING) {
/* We change from FREEZING to FROZEN lazily if the cgroup was
* only partially frozen when we exitted write. */
update_if_frozen(cgroup, freezer);
state = freezer->state;
}
spin_unlock_irq(&freezer->lock);
cgroup_unlock();
seq_puts(m, freezer_state_strs[state]);
seq_putc(m, '\n');
return 0;
}
static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
{
struct cgroup_iter it;
struct task_struct *task;
unsigned int num_cant_freeze_now = 0;
cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it))) {
if (!freeze_task(task))
continue;
if (is_task_frozen_enough(task))
continue;
if (!freezing(task) && !freezer_should_skip(task))
num_cant_freeze_now++;
}
cgroup_iter_end(cgroup, &it);
return num_cant_freeze_now ? -EBUSY : 0;
}
static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
{
struct cgroup_iter it;
struct task_struct *task;
cgroup_iter_start(cgroup, &it);
while ((task = cgroup_iter_next(cgroup, &it)))
__thaw_task(task);
cgroup_iter_end(cgroup, &it);
}
static int freezer_change_state(struct cgroup *cgroup,
enum freezer_state goal_state)
{
struct freezer *freezer;
int retval = 0;
freezer = cgroup_freezer(cgroup);
spin_lock_irq(&freezer->lock);
update_if_frozen(cgroup, freezer);
switch (goal_state) {
case CGROUP_THAWED:
if (freezer->state != CGROUP_THAWED)
atomic_dec(&system_freezing_cnt);
freezer->state = CGROUP_THAWED;
unfreeze_cgroup(cgroup, freezer);
break;
case CGROUP_FROZEN:
if (freezer->state == CGROUP_THAWED)
atomic_inc(&system_freezing_cnt);
freezer->state = CGROUP_FREEZING;
retval = try_to_freeze_cgroup(cgroup, freezer);
break;
default:
BUG();
}
spin_unlock_irq(&freezer->lock);
return retval;
}
static int freezer_write(struct cgroup *cgroup,
struct cftype *cft,
const char *buffer)
{
int retval;
enum freezer_state goal_state;
if (strcmp(buffer, freezer_state_strs[CGROUP_THAWED]) == 0)
goal_state = CGROUP_THAWED;
else if (strcmp(buffer, freezer_state_strs[CGROUP_FROZEN]) == 0)
goal_state = CGROUP_FROZEN;
else
return -EINVAL;
if (!cgroup_lock_live_group(cgroup))
return -ENODEV;
retval = freezer_change_state(cgroup, goal_state);
cgroup_unlock();
return retval;
}
static struct cftype files[] = {
{
.name = "state",
.flags = CFTYPE_NOT_ON_ROOT,
.read_seq_string = freezer_read,
.write_string = freezer_write,
},
{ } /* terminate */
};
struct cgroup_subsys freezer_subsys = {
.name = "freezer",
.create = freezer_create,
.destroy = freezer_destroy,
.subsys_id = freezer_subsys_id,
.can_attach = freezer_can_attach,
.fork = freezer_fork,
.base_cftypes = files,
/*
* freezer subsys doesn't handle hierarchy at all. Frozen state
* should be inherited through the hierarchy - if a parent is
* frozen, all its children should be frozen. Fix it and remove
* the following.
*/
.broken_hierarchy = true,
};