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Subject[PATCH 07/10] cgroups: allow subsystems to cancel a fork
Date
Let the subsystem's fork callback return an error value so that they can
cancel a fork. This is going to be used by the task counter subsystem to
implement the limit.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Aditya Kali <adityakali@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tim Hockin <thockin@hockin.org>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Containers <containers@lists.linux-foundation.org>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Cgroups <cgroups@vger.kernel.org>
Cc: Daniel J Walsh <dwalsh@redhat.com>
Cc: "Daniel P. Berrange" <berrange@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Max Kellermann <mk@cm4all.com>
Cc: Mandeep Singh Baines <msb@chromium.org>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/cgroup.h | 20 ++++++++++++++------
kernel/cgroup.c | 23 +++++++++++++++++++----
kernel/cgroup_freezer.c | 6 ++++--
kernel/exit.c | 2 +-
kernel/fork.c | 7 +++++--
5 files changed, 43 insertions(+), 15 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7da3e74..e7d3f0d 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -17,10 +17,11 @@
#include <linux/rwsem.h>
#include <linux/idr.h>

+struct cgroup_subsys;
+
#ifdef CONFIG_CGROUPS

struct cgroupfs_root;
-struct cgroup_subsys;
struct inode;
struct cgroup;
struct css_id;
@@ -32,9 +33,11 @@ extern int cgroup_lock_is_held(void);
extern bool cgroup_lock_live_group(struct cgroup *cgrp);
extern void cgroup_unlock(void);
extern void cgroup_fork(struct task_struct *p);
-extern void cgroup_fork_callbacks(struct task_struct *p);
+extern int cgroup_fork_callbacks(struct task_struct *p,
+ struct cgroup_subsys **failed_ss);
extern void cgroup_post_fork(struct task_struct *p);
-extern void cgroup_exit(struct task_struct *p, int run_callbacks);
+extern void cgroup_exit(struct task_struct *p, int run_callbacks,
+ struct cgroup_subsys *failed_ss);
extern int cgroupstats_build(struct cgroupstats *stats,
struct dentry *dentry);
extern int cgroup_load_subsys(struct cgroup_subsys *ss);
@@ -462,7 +465,7 @@ struct cgroup_subsys {
struct cgroup_taskset *tset);
void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup_taskset *tset);
- void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
+ int (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
void (*exit)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup *old_cgrp, struct task_struct *task);
int (*populate)(struct cgroup_subsys *ss,
@@ -614,9 +617,14 @@ struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
static inline int cgroup_init_early(void) { return 0; }
static inline int cgroup_init(void) { return 0; }
static inline void cgroup_fork(struct task_struct *p) {}
-static inline void cgroup_fork_callbacks(struct task_struct *p) {}
+static inline int cgroup_fork_callbacks(struct task_struct *p,
+ struct cgroup_subsys **failed_ss)
+{
+ return 0;
+}
static inline void cgroup_post_fork(struct task_struct *p) {}
-static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
+static inline void cgroup_exit(struct task_struct *p, int callbacks,
+ struct cgroup_subsys *failed_ss) {}

static inline void cgroup_lock(void) {}
static inline void cgroup_unlock(void) {}
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1626152..af38004 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4583,8 +4583,11 @@ void cgroup_fork(struct task_struct *child)
* tasklist. No need to take any locks since no-one can
* be operating on this task.
*/
-void cgroup_fork_callbacks(struct task_struct *child)
+int cgroup_fork_callbacks(struct task_struct *child,
+ struct cgroup_subsys **failed_ss)
{
+ int err;
+
if (need_forkexit_callback) {
int i;
/*
@@ -4594,10 +4597,17 @@ void cgroup_fork_callbacks(struct task_struct *child)
*/
for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
- if (ss->fork)
- ss->fork(ss, child);
+ if (ss->fork) {
+ err = ss->fork(ss, child);
+ if (err) {
+ *failed_ss = ss;
+ return err;
+ }
+ }
}
}
+
+ return 0;
}

/**
@@ -4664,7 +4674,8 @@ void cgroup_post_fork(struct task_struct *child)
* which wards off any cgroup_attach_task() attempts, or task is a failed
* fork, never visible to cgroup_attach_task.
*/
-void cgroup_exit(struct task_struct *tsk, int run_callbacks)
+void cgroup_exit(struct task_struct *tsk, int run_callbacks,
+ struct cgroup_subsys *failed_ss)
{
struct css_set *cg;
int i;
@@ -4693,6 +4704,10 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
*/
for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
+
+ if (ss == failed_ss)
+ break;
+
if (ss->exit) {
struct cgroup *old_cgrp =
rcu_dereference_raw(cg->subsys[i])->cgroup;
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index fc0646b..ec86eb7 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -185,7 +185,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
return 0;
}

-static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
+static int freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
{
struct freezer *freezer;

@@ -205,7 +205,7 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
* following check.
*/
if (!freezer->css.cgroup->parent)
- return;
+ return 0;

spin_lock_irq(&freezer->lock);
BUG_ON(freezer->state == CGROUP_FROZEN);
@@ -214,6 +214,8 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
if (freezer->state == CGROUP_FREEZING)
freeze_task(task);
spin_unlock_irq(&freezer->lock);
+
+ return 0;
}

/*
diff --git a/kernel/exit.c b/kernel/exit.c
index 294b170..e2ee0bb 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -990,7 +990,7 @@ void do_exit(long code)
*/
perf_event_exit_task(tsk);

- cgroup_exit(tsk, 1);
+ cgroup_exit(tsk, 1, NULL);

if (group_dead)
disassociate_ctty(1);
diff --git a/kernel/fork.c b/kernel/fork.c
index 051f090..617ca93 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1054,6 +1054,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
int retval;
struct task_struct *p;
int cgroup_callbacks_done = 0;
+ struct cgroup_subsys *cgroup_failed_ss = NULL;

if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
@@ -1308,8 +1309,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
/* Now that the task is set up, run cgroup callbacks if
* necessary. We need to run them before the task is visible
* on the tasklist. */
- cgroup_fork_callbacks(p);
+ retval = cgroup_fork_callbacks(p, &cgroup_failed_ss);
cgroup_callbacks_done = 1;
+ if (retval)
+ goto bad_fork_free_pid;

/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);
@@ -1413,7 +1416,7 @@ bad_fork_cleanup_cgroup:
#endif
if (clone_flags & CLONE_THREAD)
threadgroup_change_end(current);
- cgroup_exit(p, cgroup_callbacks_done);
+ cgroup_exit(p, cgroup_callbacks_done, cgroup_failed_ss);
delayacct_tsk_free(p);
module_put(task_thread_info(p)->exec_domain->module);
bad_fork_cleanup_count:
--
1.7.5.4


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