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Merge branch 'for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 

Pull cgroup updates from Tejun Heo:

 - a new PIDs controller is added.  It turns out that PIDs are actually
   an independent resource from kmem due to the limited PID space.

 - more core preparations for the v2 interface.  Once cpu side interface
   is settled, it should be ready for lifting the devel mask.
   for-4.3-unified-base was temporarily branched so that other trees
   (block) can pull cgroup core changes that blkcg changes depend on.

 - a non-critical idr_preload usage bug fix.

* 'for-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: pids: fix invalid get/put usage
  cgroup: introduce cgroup_subsys->legacy_name
  cgroup: don't print subsystems for the default hierarchy
  cgroup: make cftype->private a unsigned long
  cgroup: export cgrp_dfl_root
  cgroup: define controller file conventions
  cgroup: fix idr_preload usage
  cgroup: add documentation for the PIDs controller
  cgroup: implement the PIDs subsystem
  cgroup: allow a cgroup subsystem to reject a fork
This commit is contained in:
Linus Torvalds 2015-09-02 08:04:23 -07:00
parent 76ec51ef5e 20f1f4b5ff
commit 8bdc69b764
14 changed files with 717 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
CREDITS
View File

@ -3219,6 +3219,11 @@ S: 69 rue Dunois
S: 75013 Paris
S: France
N: Aleksa Sarai
E: cyphar@cyphar.com
W: https://www.cyphar.com/
D: `pids` cgroup subsystem
N: Dipankar Sarma
E: dipankar@in.ibm.com
D: RCU

2
Documentation/cgroups/00-INDEX
View File

@ -22,6 +22,8 @@ net_cls.txt
- Network classifier cgroups details and usages.
net_prio.txt
- Network priority cgroups details and usages.
pids.txt
- Process number cgroups details and usages.
resource_counter.txt
- Resource Counter API.
unified-hierarchy.txt

85
Documentation/cgroups/pids.txt Normal file
View File

@ -0,0 +1,85 @@
Process Number Controller
=========================
Abstract
--------
The process number controller is used to allow a cgroup hierarchy to stop any
new tasks from being fork()'d or clone()'d after a certain limit is reached.
Since it is trivial to hit the task limit without hitting any kmemcg limits in
place, PIDs are a fundamental resource. As such, PID exhaustion must be
preventable in the scope of a cgroup hierarchy by allowing resource limiting of
the number of tasks in a cgroup.
Usage
-----
In order to use the `pids` controller, set the maximum number of tasks in
pids.max (this is not available in the root cgroup for obvious reasons). The
number of processes currently in the cgroup is given by pids.current.
Organisational operations are not blocked by cgroup policies, so it is possible
to have pids.current > pids.max. This can be done by either setting the limit to
be smaller than pids.current, or attaching enough processes to the cgroup such
that pids.current > pids.max. However, it is not possible to violate a cgroup
policy through fork() or clone(). fork() and clone() will return -EAGAIN if the
creation of a new process would cause a cgroup policy to be violated.
To set a cgroup to have no limit, set pids.max to "max". This is the default for
all new cgroups (N.B. that PID limits are hierarchical, so the most stringent
limit in the hierarchy is followed).
pids.current tracks all child cgroup hierarchies, so parent/pids.current is a
superset of parent/child/pids.current.
Example
-------
First, we mount the pids controller:
# mkdir -p /sys/fs/cgroup/pids
# mount -t cgroup -o pids none /sys/fs/cgroup/pids
Then we create a hierarchy, set limits and attach processes to it:
# mkdir -p /sys/fs/cgroup/pids/parent/child
# echo 2 > /sys/fs/cgroup/pids/parent/pids.max
# echo $$ > /sys/fs/cgroup/pids/parent/cgroup.procs
# cat /sys/fs/cgroup/pids/parent/pids.current
2
#
It should be noted that attempts to overcome the set limit (2 in this case) will
fail:
# cat /sys/fs/cgroup/pids/parent/pids.current
2
# ( /bin/echo "Here's some processes for you." | cat )
sh: fork: Resource temporary unavailable
#
Even if we migrate to a child cgroup (which doesn't have a set limit), we will
not be able to overcome the most stringent limit in the hierarchy (in this case,
parent's):
# echo $$ > /sys/fs/cgroup/pids/parent/child/cgroup.procs
# cat /sys/fs/cgroup/pids/parent/pids.current
2
# cat /sys/fs/cgroup/pids/parent/child/pids.current
2
# cat /sys/fs/cgroup/pids/parent/child/pids.max
max
# ( /bin/echo "Here's some processes for you." | cat )
sh: fork: Resource temporary unavailable
#
We can set a limit that is smaller than pids.current, which will stop any new
processes from being forked at all (note that the shell itself counts towards
pids.current):
# echo 1 > /sys/fs/cgroup/pids/parent/pids.max
# /bin/echo "We can't even spawn a single process now."
sh: fork: Resource temporary unavailable
# echo 0 > /sys/fs/cgroup/pids/parent/pids.max
# /bin/echo "We can't even spawn a single process now."
sh: fork: Resource temporary unavailable
#

80
Documentation/cgroups/unified-hierarchy.txt
View File

@ -23,10 +23,13 @@ CONTENTS
5. Other Changes
5-1. [Un]populated Notification
5-2. Other Core Changes
5-3. Per-Controller Changes
5-3-1. blkio
5-3-2. cpuset
5-3-3. memory
5-3. Controller File Conventions
5-3-1. Format
5-3-2. Control Knobs
5-4. Per-Controller Changes
5-4-1. blkio
5-4-2. cpuset
5-4-3. memory
6. Planned Changes
6-1. CAP for resource control
@ -372,14 +375,75 @@ supported and the interface files "release_agent" and
- The "cgroup.clone_children" file is removed.
5-3. Per-Controller Changes
5-3. Controller File Conventions
5-3-1. blkio
5-3-1. Format
In general, all controller files should be in one of the following
formats whenever possible.
- Values only files
VAL0 VAL1...\n
- Flat keyed files
KEY0 VAL0\n
KEY1 VAL1\n
...
- Nested keyed files
KEY0 SUB_KEY0=VAL00 SUB_KEY1=VAL01...
KEY1 SUB_KEY0=VAL10 SUB_KEY1=VAL11...
...
For a writeable file, the format for writing should generally match
reading; however, controllers may allow omitting later fields or
implement restricted shortcuts for most common use cases.
For both flat and nested keyed files, only the values for a single key
can be written at a time. For nested keyed files, the sub key pairs
may be specified in any order and not all pairs have to be specified.
5-3-2. Control Knobs
- Settings for a single feature should generally be implemented in a
single file.
- In general, the root cgroup should be exempt from resource control
and thus shouldn't have resource control knobs.
- If a controller implements ratio based resource distribution, the
control knob should be named "weight" and have the range [1, 10000]
and 100 should be the default value. The values are chosen to allow
enough and symmetric bias in both directions while keeping it
intuitive (the default is 100%).
- If a controller implements an absolute resource guarantee and/or
limit, the control knobs should be named "min" and "max"
respectively. If a controller implements best effort resource
gurantee and/or limit, the control knobs should be named "low" and
"high" respectively.
In the above four control files, the special token "max" should be
used to represent upward infinity for both reading and writing.
- If a setting has configurable default value and specific overrides,
the default settings should be keyed with "default" and appear as
the first entry in the file. Specific entries can use "default" as
its value to indicate inheritance of the default value.
5-4. Per-Controller Changes
5-4-1. blkio
- blk-throttle becomes properly hierarchical.
5-3-2. cpuset
5-4-2. cpuset
- Tasks are kept in empty cpusets after hotplug and take on the masks
of the nearest non-empty ancestor, instead of being moved to it.
@ -388,7 +452,7 @@ supported and the interface files "release_agent" and
masks of the nearest non-empty ancestor.
5-3-3. memory
5-4-3. memory
- use_hierarchy is on by default and the cgroup file for the flag is
not created.

15
include/linux/cgroup-defs.h
View File

@ -34,12 +34,17 @@ struct seq_file;
/* define the enumeration of all cgroup subsystems */
#define SUBSYS(_x) _x ## _cgrp_id,
#define SUBSYS_TAG(_t) CGROUP_ ## _t, \
__unused_tag_ ## _t = CGROUP_ ## _t - 1,
enum cgroup_subsys_id {
#include <linux/cgroup_subsys.h>
CGROUP_SUBSYS_COUNT,
};
#undef SUBSYS_TAG
#undef SUBSYS
#define CGROUP_CANFORK_COUNT (CGROUP_CANFORK_END - CGROUP_CANFORK_START)
/* bits in struct cgroup_subsys_state flags field */
enum {
CSS_NO_REF = (1 << 0), /* no reference counting for this css */
@ -318,7 +323,7 @@ struct cftype {
* end of cftype array.
*/
char name[MAX_CFTYPE_NAME];
int private;
unsigned long private;
/*
* If not 0, file mode is set to this value, otherwise it will
* be figured out automatically
@ -406,7 +411,9 @@ struct cgroup_subsys {
struct cgroup_taskset *tset);
void (*attach)(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset);
void (*fork)(struct task_struct *task);
int (*can_fork)(struct task_struct *task, void **priv_p);
void (*cancel_fork)(struct task_struct *task, void *priv);
void (*fork)(struct task_struct *task, void *priv);
void (*exit)(struct cgroup_subsys_state *css,
struct cgroup_subsys_state *old_css,
struct task_struct *task);
@ -434,6 +441,9 @@ struct cgroup_subsys {
int id;
const char *name;
/* optional, initialized automatically during boot if not set */
const char *legacy_name;
/* link to parent, protected by cgroup_lock() */
struct cgroup_root *root;
@ -491,6 +501,7 @@ static inline void cgroup_threadgroup_change_end(struct task_struct *tsk)
#else /* CONFIG_CGROUPS */
#define CGROUP_CANFORK_COUNT 0
#define CGROUP_SUBSYS_COUNT 0
static inline void cgroup_threadgroup_change_begin(struct task_struct *tsk) {}

24
include/linux/cgroup.h
View File

@ -22,6 +22,15 @@
#ifdef CONFIG_CGROUPS
/*
* All weight knobs on the default hierarhcy should use the following min,
* default and max values. The default value is the logarithmic center of
* MIN and MAX and allows 100x to be expressed in both directions.
*/
#define CGROUP_WEIGHT_MIN 1
#define CGROUP_WEIGHT_DFL 100
#define CGROUP_WEIGHT_MAX 10000
/* a css_task_iter should be treated as an opaque object */
struct css_task_iter {
struct cgroup_subsys *ss;
@ -62,7 +71,12 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *tsk);
void cgroup_fork(struct task_struct *p);
void cgroup_post_fork(struct task_struct *p);
extern int cgroup_can_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]);
extern void cgroup_cancel_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]);
extern void cgroup_post_fork(struct task_struct *p,
void *old_ss_priv[CGROUP_CANFORK_COUNT]);
void cgroup_exit(struct task_struct *p);
int cgroup_init_early(void);
@ -524,7 +538,13 @@ static inline int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry) { return -EINVAL; }
static inline void cgroup_fork(struct task_struct *p) {}
static inline void cgroup_post_fork(struct task_struct *p) {}
static inline int cgroup_can_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT])
{ return 0; }
static inline void cgroup_cancel_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]) {}
static inline void cgroup_post_fork(struct task_struct *p,
void *ss_priv[CGROUP_CANFORK_COUNT]) {}
static inline void cgroup_exit(struct task_struct *p) {}
static inline int cgroup_init_early(void) { return 0; }

28
include/linux/cgroup_subsys.h
View File

@ -3,6 +3,17 @@
*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/
/*
* This file *must* be included with SUBSYS() defined.
* SUBSYS_TAG() is a noop if undefined.
*/
#ifndef SUBSYS_TAG
#define __TMP_SUBSYS_TAG
#define SUBSYS_TAG(_x)
#endif
#if IS_ENABLED(CONFIG_CPUSETS)
SUBSYS(cpuset)
#endif
@ -47,12 +58,29 @@ SUBSYS(net_prio)
SUBSYS(hugetlb)
#endif
/*
* Subsystems that implement the can_fork() family of callbacks.
*/
SUBSYS_TAG(CANFORK_START)
#if IS_ENABLED(CONFIG_CGROUP_PIDS)
SUBSYS(pids)
#endif
SUBSYS_TAG(CANFORK_END)
/*
* The following subsystems are not supported on the default hierarchy.
*/
#if IS_ENABLED(CONFIG_CGROUP_DEBUG)
SUBSYS(debug)
#endif
#ifdef __TMP_SUBSYS_TAG
#undef __TMP_SUBSYS_TAG
#undef SUBSYS_TAG
#endif
/*
* DO NOT ADD ANY SUBSYSTEM WITHOUT EXPLICIT ACKS FROM CGROUP MAINTAINERS.
*/

16
init/Kconfig
View File

@ -947,6 +947,22 @@ config CGROUP_FREEZER
Provides a way to freeze and unfreeze all tasks in a
cgroup.
config CGROUP_PIDS
bool "PIDs cgroup subsystem"
help
Provides enforcement of process number limits in the scope of a
cgroup. Any attempt to fork more processes than is allowed in the
cgroup will fail. PIDs are fundamentally a global resource because it
is fairly trivial to reach PID exhaustion before you reach even a
conservative kmemcg limit. As a result, it is possible to grind a
system to halt without being limited by other cgroup policies. The
PIDs cgroup subsystem is designed to stop this from happening.
It should be noted that organisational operations (such as attaching
to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
since the PIDs limit only affects a process's ability to fork, not to
attach to a cgroup.
config CGROUP_DEVICE
bool "Device controller for cgroups"
help

1
kernel/Makefile
View File

@ -55,6 +55,7 @@ obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o
obj-$(CONFIG_COMPAT) += compat.o
obj-$(CONFIG_CGROUPS) += cgroup.o
obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
obj-$(CONFIG_CGROUP_PIDS) += cgroup_pids.o
obj-$(CONFIG_CPUSETS) += cpuset.o
obj-$(CONFIG_UTS_NS) += utsname.o
obj-$(CONFIG_USER_NS) += user_namespace.o

122
kernel/cgroup.c
View File

@ -145,6 +145,7 @@ static const char *cgroup_subsys_name[] = {
* part of that cgroup.
*/
struct cgroup_root cgrp_dfl_root;
EXPORT_SYMBOL_GPL(cgrp_dfl_root);
/*
* The default hierarchy always exists but is hidden until mounted for the
@ -186,6 +187,9 @@ static u64 css_serial_nr_next = 1;
static unsigned long have_fork_callback __read_mostly;
static unsigned long have_exit_callback __read_mostly;
/* Ditto for the can_fork callback. */
static unsigned long have_canfork_callback __read_mostly;
static struct cftype cgroup_dfl_base_files[];
static struct cftype cgroup_legacy_base_files[];
@ -207,7 +211,7 @@ static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
idr_preload(gfp_mask);
spin_lock_bh(&cgroup_idr_lock);
ret = idr_alloc(idr, ptr, start, end, gfp_mask);
ret = idr_alloc(idr, ptr, start, end, gfp_mask & ~__GFP_WAIT);
spin_unlock_bh(&cgroup_idr_lock);
idr_preload_end();
return ret;
@ -1027,10 +1031,13 @@ static const struct file_operations proc_cgroupstats_operations;
static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
char *buf)
{
struct cgroup_subsys *ss = cft->ss;
if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
!(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
cft->ss->name, cft->name);
cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
cft->name);
else
strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
return buf;
@ -1332,9 +1339,10 @@ static int cgroup_show_options(struct seq_file *seq,
struct cgroup_subsys *ss;
int ssid;
for_each_subsys(ss, ssid)
if (root->subsys_mask & (1 << ssid))
seq_printf(seq, ",%s", ss->name);
if (root != &cgrp_dfl_root)
for_each_subsys(ss, ssid)
if (root->subsys_mask & (1 << ssid))
seq_printf(seq, ",%s", ss->legacy_name);
if (root->flags & CGRP_ROOT_NOPREFIX)
seq_puts(seq, ",noprefix");
if (root->flags & CGRP_ROOT_XATTR)
@ -1447,7 +1455,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
}
for_each_subsys(ss, i) {
if (strcmp(token, ss->name))
if (strcmp(token, ss->legacy_name))
continue;
if (ss->disabled)
continue;
@ -1666,7 +1674,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
lockdep_assert_held(&cgroup_mutex);
ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_NOWAIT);
ret = cgroup_idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
if (ret < 0)
goto out;
root_cgrp->id = ret;
@ -4579,7 +4587,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
if (err)
goto err_free_css;
err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_NOWAIT);
err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
if (err < 0)
goto err_free_percpu_ref;
css->id = err;
@ -4656,7 +4664,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
* Temporarily set the pointer to NULL, so idr_find() won't return
* a half-baked cgroup.
*/
cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_NOWAIT);
cgrp->id = cgroup_idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
if (cgrp->id < 0) {
ret = -ENOMEM;
goto out_cancel_ref;
@ -4955,6 +4963,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
have_fork_callback |= (bool)ss->fork << ss->id;
have_exit_callback |= (bool)ss->exit << ss->id;
have_canfork_callback |= (bool)ss->can_fork << ss->id;
/* At system boot, before all subsystems have been
* registered, no tasks have been forked, so we don't
@ -4993,6 +5002,8 @@ int __init cgroup_init_early(void)
ss->id = i;
ss->name = cgroup_subsys_name[i];
if (!ss->legacy_name)
ss->legacy_name = cgroup_subsys_name[i];
if (ss->early_init)
cgroup_init_subsys(ss, true);
@ -5136,9 +5147,11 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
continue;
seq_printf(m, "%d:", root->hierarchy_id);
for_each_subsys(ss, ssid)
if (root->subsys_mask & (1 << ssid))
seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
if (root != &cgrp_dfl_root)
for_each_subsys(ss, ssid)
if (root->subsys_mask & (1 << ssid))
seq_printf(m, "%s%s", count++ ? "," : "",
ss->legacy_name);
if (strlen(root->name))
seq_printf(m, "%sname=%s", count ? "," : "",
root->name);
@ -5178,7 +5191,7 @@ static int proc_cgroupstats_show(struct seq_file *m, void *v)
for_each_subsys(ss, i)
seq_printf(m, "%s\t%d\t%d\t%d\n",
ss->name, ss->root->hierarchy_id,
ss->legacy_name, ss->root->hierarchy_id,
atomic_read(&ss->root->nr_cgrps), !ss->disabled);
mutex_unlock(&cgroup_mutex);
@ -5197,6 +5210,19 @@ static const struct file_operations proc_cgroupstats_operations = {
.release = single_release,
};
static void **subsys_canfork_priv_p(void *ss_priv[CGROUP_CANFORK_COUNT], int i)
{
if (CGROUP_CANFORK_START <= i && i < CGROUP_CANFORK_END)
return &ss_priv[i - CGROUP_CANFORK_START];
return NULL;
}
static void *subsys_canfork_priv(void *ss_priv[CGROUP_CANFORK_COUNT], int i)
{
void **private = subsys_canfork_priv_p(ss_priv, i);
return private ? *private : NULL;
}
/**
* cgroup_fork - initialize cgroup related fields during copy_process()
* @child: pointer to task_struct of forking parent process.
@ -5211,6 +5237,57 @@ void cgroup_fork(struct task_struct *child)
INIT_LIST_HEAD(&child->cg_list);
}
/**
* cgroup_can_fork - called on a new task before the process is exposed
* @child: the task in question.
*
* This calls the subsystem can_fork() callbacks. If the can_fork() callback
* returns an error, the fork aborts with that error code. This allows for
* a cgroup subsystem to conditionally allow or deny new forks.
*/
int cgroup_can_fork(struct task_struct *child,
void *ss_priv[CGROUP_CANFORK_COUNT])
{
struct cgroup_subsys *ss;
int i, j, ret;
for_each_subsys_which(ss, i, &have_canfork_callback) {
ret = ss->can_fork(child, subsys_canfork_priv_p(ss_priv, i));
if (ret)
goto out_revert;
}
return 0;
out_revert:
for_each_subsys(ss, j) {
if (j >= i)
break;
if (ss->cancel_fork)
ss->cancel_fork(child, subsys_canfork_priv(ss_priv, j));
}
return ret;
}
/**
* cgroup_cancel_fork - called if a fork failed after cgroup_can_fork()
* @child: the task in question
*
* This calls the cancel_fork() callbacks if a fork failed *after*
* cgroup_can_fork() succeded.
*/
void cgroup_cancel_fork(struct task_struct *child,
void *ss_priv[CGROUP_CANFORK_COUNT])
{
struct cgroup_subsys *ss;
int i;
for_each_subsys(ss, i)
if (ss->cancel_fork)
ss->cancel_fork(child, subsys_canfork_priv(ss_priv, i));
}
/**
* cgroup_post_fork - called on a new task after adding it to the task list
* @child: the task in question
@ -5221,7 +5298,8 @@ void cgroup_fork(struct task_struct *child)
* cgroup_task_iter_start() - to guarantee that the new task ends up on its
* list.
*/
void cgroup_post_fork(struct task_struct *child)
void cgroup_post_fork(struct task_struct *child,
void *old_ss_priv[CGROUP_CANFORK_COUNT])
{
struct cgroup_subsys *ss;
int i;
@ -5266,7 +5344,7 @@ void cgroup_post_fork(struct task_struct *child)
* and addition to css_set.
*/
for_each_subsys_which(ss, i, &have_fork_callback)
ss->fork(child);
ss->fork(child, subsys_canfork_priv(old_ss_priv, i));
}
/**
@ -5400,12 +5478,14 @@ static int __init cgroup_disable(char *str)
continue;
for_each_subsys(ss, i) {
if (!strcmp(token, ss->name)) {
ss->disabled = 1;
printk(KERN_INFO "Disabling %s control group"
" subsystem\n", ss->name);
break;
}
if (strcmp(token, ss->name) &&
strcmp(token, ss->legacy_name))
continue;
ss->disabled = 1;
printk(KERN_INFO "Disabling %s control group subsystem\n",
ss->name);
break;
}
}
return 1;

2
kernel/cgroup_freezer.c
View File

@ -203,7 +203,7 @@ static void freezer_attach(struct cgroup_subsys_state *new_css,
* to do anything as freezer_attach() will put @task into the appropriate
* state.
*/
static void freezer_fork(struct task_struct *task)
static void freezer_fork(struct task_struct *task, void *private)
{
struct freezer *freezer;

355
kernel/cgroup_pids.c Normal file
View File

@ -0,0 +1,355 @@
/*
* Process number limiting controller for cgroups.
*
* Used to allow a cgroup hierarchy to stop any new processes from fork()ing
* after a certain limit is reached.
*
* Since it is trivial to hit the task limit without hitting any kmemcg limits
* in place, PIDs are a fundamental resource. As such, PID exhaustion must be
* preventable in the scope of a cgroup hierarchy by allowing resource limiting
* of the number of tasks in a cgroup.
*
* In order to use the `pids` controller, set the maximum number of tasks in
* pids.max (this is not available in the root cgroup for obvious reasons). The
* number of processes currently in the cgroup is given by pids.current.
* Organisational operations are not blocked by cgroup policies, so it is
* possible to have pids.current > pids.max. However, it is not possible to
* violate a cgroup policy through fork(). fork() will return -EAGAIN if forking
* would cause a cgroup policy to be violated.
*
* To set a cgroup to have no limit, set pids.max to "max". This is the default
* for all new cgroups (N.B. that PID limits are hierarchical, so the most
* stringent limit in the hierarchy is followed).
*
* pids.current tracks all child cgroup hierarchies, so parent/pids.current is
* a superset of parent/child/pids.current.
*
* Copyright (C) 2015 Aleksa Sarai <cyphar@cyphar.com>
*
* This file is subject to the terms and conditions of version 2 of the GNU
* General Public License. See the file COPYING in the main directory of the
* Linux distribution for more details.
*/
#include <linux/kernel.h>
#include <linux/threads.h>
#include <linux/atomic.h>
#include <linux/cgroup.h>
#include <linux/slab.h>
#define PIDS_MAX (PID_MAX_LIMIT + 1ULL)
#define PIDS_MAX_STR "max"
struct pids_cgroup {
struct cgroup_subsys_state css;
/*
* Use 64-bit types so that we can safely represent "max" as
* %PIDS_MAX = (%PID_MAX_LIMIT + 1).
*/
atomic64_t counter;
int64_t limit;
};
static struct pids_cgroup *css_pids(struct cgroup_subsys_state *css)
{
return container_of(css, struct pids_cgroup, css);
}
static struct pids_cgroup *parent_pids(struct pids_cgroup *pids)
{
return css_pids(pids->css.parent);
}
static struct cgroup_subsys_state *
pids_css_alloc(struct cgroup_subsys_state *parent)
{
struct pids_cgroup *pids;
pids = kzalloc(sizeof(struct pids_cgroup), GFP_KERNEL);
if (!pids)
return ERR_PTR(-ENOMEM);
pids->limit = PIDS_MAX;
atomic64_set(&pids->counter, 0);
return &pids->css;
}
static void pids_css_free(struct cgroup_subsys_state *css)
{
kfree(css_pids(css));
}
/**
* pids_cancel - uncharge the local pid count
* @pids: the pid cgroup state
* @num: the number of pids to cancel
*
* This function will WARN if the pid count goes under 0, because such a case is
* a bug in the pids controller proper.
*/
static void pids_cancel(struct pids_cgroup *pids, int num)
{
/*
* A negative count (or overflow for that matter) is invalid,
* and indicates a bug in the `pids` controller proper.
*/
WARN_ON_ONCE(atomic64_add_negative(-num, &pids->counter));
}
/**
* pids_uncharge - hierarchically uncharge the pid count
* @pids: the pid cgroup state
* @num: the number of pids to uncharge
*/
static void pids_uncharge(struct pids_cgroup *pids, int num)
{
struct pids_cgroup *p;
for (p = pids; p; p = parent_pids(p))
pids_cancel(p, num);
}
/**
* pids_charge - hierarchically charge the pid count
* @pids: the pid cgroup state
* @num: the number of pids to charge
*
* This function does *not* follow the pid limit set. It cannot fail and the new
* pid count may exceed the limit. This is only used for reverting failed
* attaches, where there is no other way out than violating the limit.
*/
static void pids_charge(struct pids_cgroup *pids, int num)
{
struct pids_cgroup *p;
for (p = pids; p; p = parent_pids(p))
atomic64_add(num, &p->counter);
}
/**
* pids_try_charge - hierarchically try to charge the pid count
* @pids: the pid cgroup state
* @num: the number of pids to charge
*
* This function follows the set limit. It will fail if the charge would cause
* the new value to exceed the hierarchical limit. Returns 0 if the charge
* succeded, otherwise -EAGAIN.
*/
static int pids_try_charge(struct pids_cgroup *pids, int num)
{
struct pids_cgroup *p, *q;
for (p = pids; p; p = parent_pids(p)) {
int64_t new = atomic64_add_return(num, &p->counter);
/*
* Since new is capped to the maximum number of pid_t, if
* p->limit is %PIDS_MAX then we know that this test will never
* fail.
*/
if (new > p->limit)
goto revert;
}
return 0;
revert:
for (q = pids; q != p; q = parent_pids(q))
pids_cancel(q, num);
pids_cancel(p, num);
return -EAGAIN;
}
static int pids_can_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct pids_cgroup *pids = css_pids(css);
struct task_struct *task;
cgroup_taskset_for_each(task, tset) {
struct cgroup_subsys_state *old_css;
struct pids_cgroup *old_pids;
/*
* No need to pin @old_css between here and cancel_attach()
* because cgroup core protects it from being freed before
* the migration completes or fails.
*/
old_css = task_css(task, pids_cgrp_id);
old_pids = css_pids(old_css);
pids_charge(pids, 1);
pids_uncharge(old_pids, 1);
}
return 0;
}
static void pids_cancel_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
struct pids_cgroup *pids = css_pids(css);
struct task_struct *task;
cgroup_taskset_for_each(task, tset) {
struct cgroup_subsys_state *old_css;
struct pids_cgroup *old_pids;
old_css = task_css(task, pids_cgrp_id);
old_pids = css_pids(old_css);
pids_charge(old_pids, 1);
pids_uncharge(pids, 1);
}
}
static int pids_can_fork(struct task_struct *task, void **priv_p)
{
struct cgroup_subsys_state *css;
struct pids_cgroup *pids;
int err;
/*
* Use the "current" task_css for the pids subsystem as the tentative
* css. It is possible we will charge the wrong hierarchy, in which
* case we will forcefully revert/reapply the charge on the right
* hierarchy after it is committed to the task proper.
*/
css = task_get_css(current, pids_cgrp_id);
pids = css_pids(css);
err = pids_try_charge(pids, 1);
if (err)
goto err_css_put;
*priv_p = css;
return 0;
err_css_put:
css_put(css);
return err;
}
static void pids_cancel_fork(struct task_struct *task, void *priv)
{
struct cgroup_subsys_state *css = priv;
struct pids_cgroup *pids = css_pids(css);
pids_uncharge(pids, 1);
css_put(css);
}
static void pids_fork(struct task_struct *task, void *priv)
{
struct cgroup_subsys_state *css;
struct cgroup_subsys_state *old_css = priv;
struct pids_cgroup *pids;
struct pids_cgroup *old_pids = css_pids(old_css);
css = task_get_css(task, pids_cgrp_id);
pids = css_pids(css);
/*
* If the association has changed, we have to revert and reapply the
* charge/uncharge on the wrong hierarchy to the current one. Since
* the association can only change due to an organisation event, its
* okay for us to ignore the limit in this case.
*/
if (pids != old_pids) {
pids_uncharge(old_pids, 1);
pids_charge(pids, 1);
}
css_put(css);
css_put(old_css);
}
static void pids_exit(struct cgroup_subsys_state *css,
struct cgroup_subsys_state *old_css,
struct task_struct *task)
{
struct pids_cgroup *pids = css_pids(old_css);
pids_uncharge(pids, 1);
}
static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
struct cgroup_subsys_state *css = of_css(of);
struct pids_cgroup *pids = css_pids(css);
int64_t limit;
int err;
buf = strstrip(buf);
if (!strcmp(buf, PIDS_MAX_STR)) {
limit = PIDS_MAX;
goto set_limit;
}
err = kstrtoll(buf, 0, &limit);
if (err)
return err;
if (limit < 0 || limit >= PIDS_MAX)
return -EINVAL;
set_limit:
/*
* Limit updates don't need to be mutex'd, since it isn't
* critical that any racing fork()s follow the new limit.
*/
pids->limit = limit;
return nbytes;
}
static int pids_max_show(struct seq_file *sf, void *v)
{
struct cgroup_subsys_state *css = seq_css(sf);
struct pids_cgroup *pids = css_pids(css);
int64_t limit = pids->limit;
if (limit >= PIDS_MAX)
seq_printf(sf, "%s\n", PIDS_MAX_STR);
else
seq_printf(sf, "%lld\n", limit);
return 0;
}
static s64 pids_current_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
struct pids_cgroup *pids = css_pids(css);
return atomic64_read(&pids->counter);
}
static struct cftype pids_files[] = {
{
.name = "max",
.write = pids_max_write,
.seq_show = pids_max_show,
.flags = CFTYPE_NOT_ON_ROOT,
},
{
.name = "current",
.read_s64 = pids_current_read,
},
{ } /* terminate */
};
struct cgroup_subsys pids_cgrp_subsys = {
.css_alloc = pids_css_alloc,
.css_free = pids_css_free,
.can_attach = pids_can_attach,
.cancel_attach = pids_cancel_attach,
.can_fork = pids_can_fork,
.cancel_fork = pids_cancel_fork,
.fork = pids_fork,
.exit = pids_exit,
.legacy_cftypes = pids_files,
.dfl_cftypes = pids_files,
};

17
kernel/fork.c
View File

@ -1246,6 +1246,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
{
int retval;
struct task_struct *p;
void *cgrp_ss_priv[CGROUP_CANFORK_COUNT] = {};
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
@ -1517,6 +1518,16 @@ static struct task_struct *copy_process(unsigned long clone_flags,
INIT_LIST_HEAD(&p->thread_group);
p->task_works = NULL;
/*
* Ensure that the cgroup subsystem policies allow the new process to be
* forked. It should be noted the the new process's css_set can be changed
* between here and cgroup_post_fork() if an organisation operation is in
* progress.
*/
retval = cgroup_can_fork(p, cgrp_ss_priv);
if (retval)
goto bad_fork_free_pid;
/*
* Make it visible to the rest of the system, but dont wake it up yet.
* Need tasklist lock for parent etc handling!
@ -1553,7 +1564,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
spin_unlock(&current->sighand->siglock);
write_unlock_irq(&tasklist_lock);
retval = -ERESTARTNOINTR;
goto bad_fork_free_pid;
goto bad_fork_cancel_cgroup;
}
if (likely(p->pid)) {
@ -1595,7 +1606,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
write_unlock_irq(&tasklist_lock);
proc_fork_connector(p);
cgroup_post_fork(p);
cgroup_post_fork(p, cgrp_ss_priv);
if (clone_flags & CLONE_THREAD)
threadgroup_change_end(current);
perf_event_fork(p);
@ -1605,6 +1616,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
return p;
bad_fork_cancel_cgroup:
cgroup_cancel_fork(p, cgrp_ss_priv);
bad_fork_free_pid:
if (pid != &init_struct_pid)
free_pid(pid);

2
kernel/sched/core.c
View File

@ -8133,7 +8133,7 @@ static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css)
sched_offline_group(tg);
}
static void cpu_cgroup_fork(struct task_struct *task)
static void cpu_cgroup_fork(struct task_struct *task, void *private)
{
sched_move_task(task);
}