Re: [PATCH 09/10] cgroups: Allow subsystems to cancel a fork

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Mon, Oct 03, 2011 at 09:07:11PM +0200, Frederic Weisbecker wrote:
> 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>

Acked-by: Kirill A. Shutemov <kirill@shutemov.name>

> 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: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kay Sievers <kay.sievers@vrfy.org>
> Cc: Tim Hockin <thockin@hockin.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Kirill A. Shutemov <kirill@shutemov.name>
> Cc: Containers <containers@lists.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 b62cf5e..9c8151e 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);
> @@ -479,7 +482,7 @@ struct cgroup_subsys {
>  			    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,
> @@ -636,9 +639,14 @@ 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 709baef..018df9d 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -4540,8 +4540,11 @@ 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;
>  		/*
> @@ -4551,10 +4554,17 @@ 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;
>  }
>  
>  /**
> @@ -4612,7 +4622,8 @@ 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;
> @@ -4641,6 +4652,10 @@ 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 c1421a1..30a4332 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -187,7 +187,7 @@ static int freezer_can_attach_task(struct cgroup *cgrp, struct cgroup *old_cgrp,
>  	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;
>  
> @@ -207,7 +207,7 @@ 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);
> @@ -216,6 +216,8 @@ 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/exit.c b/kernel/exit.c
> index 2913b35..abab32b 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -994,7 +994,7 @@ NORET_TYPE 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 8e6b6f4..ee8abdb 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1058,6 +1058,7 @@ 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);
> @@ -1312,8 +1313,10 @@ 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);
> @@ -1419,7 +1422,7 @@ bad_fork_cleanup_cgroup:
>  #endif
>  	if (clone_flags & CLONE_THREAD)
>  		threadgroup_fork_read_unlock(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
> 

-- 
 Kirill A. Shutemov