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Subject[RFC PATCH 1/4] cgroups: Allow a cgroup subsys to reject a fork
Date
Make the cgroup subsystem fork callback return a value
so that subsystems are able to accept or reject a fork
completion with a custom error value.

This prepares for implementing rlimit in cgroups scope.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/cgroup.h | 9 ++++++---
kernel/cgroup.c | 13 ++++++++++---
kernel/cgroup_freezer.c | 6 ++++--
kernel/fork.c | 5 ++++-
4 files changed, 24 insertions(+), 9 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ab4ac0c..07213af 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -32,7 +32,7 @@ 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);
extern void cgroup_post_fork(struct task_struct *p);
extern void cgroup_exit(struct task_struct *p, int run_callbacks);
extern int cgroupstats_build(struct cgroupstats *stats,
@@ -475,7 +475,7 @@ struct cgroup_subsys {
void (*attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup *old_cgrp, struct task_struct *tsk);
- 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,
@@ -633,7 +633,10 @@ 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)
+{
+ return 0;
+}
static inline void cgroup_post_fork(struct task_struct *p) {}
static inline void cgroup_exit(struct task_struct *p, int callbacks) {}

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2731d11..688be3d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4514,10 +4514,12 @@ 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)
{
if (need_forkexit_callback) {
int i;
+ int ret;
+
/*
* forkexit callbacks are only supported for builtin
* subsystems, and the builtin section of the subsys array is
@@ -4525,10 +4527,15 @@ 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) {
+ ret = ss->fork(ss, child);
+ if (ret)
+ return ret;
+ }
}
}
+
+ return 0;
}

/**
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index e691818..e704be6 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -186,7 +186,7 @@ static int freezer_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
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;

@@ -206,7 +206,7 @@ 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);
@@ -215,6 +215,8 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
if (freezer->state == CGROUP_FREEZING)
freeze_task(task, true);
spin_unlock_irq(&freezer->lock);
+
+ return 0;
}

/*
diff --git a/kernel/fork.c b/kernel/fork.c
index 0276c30..2625461 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1298,7 +1298,10 @@ 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);
+ if (retval)
+ goto bad_fork_free_pid;
+
cgroup_callbacks_done = 1;

/* Need tasklist lock for parent etc handling! */
--
1.7.5.4


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