[Devel] Re: [PATCH v21 015/100] cgroup freezer: Update stale locking comments

[Rafael J. Wysocki]

On Saturday 01 May 2010, Oren Laadan wrote:
> From: Matt Helsley <matthltc at us.ibm.com>
> 
> Update stale comments regarding locking order and add a little more detail
> so it's easier to follow the locking between the cgroup freezer and the
> power management freezer code.

I guess these three patches are for me.

Do you want me to handle them?

Rafael


> Signed-off-by: Matt Helsley <matthltc at us.ibm.com>
> Cc: Oren Laadan <orenl at cs.columbia.edu>
> Cc: Cedric Le Goater <legoater at free.fr>
> Cc: Paul Menage <menage at google.com>
> Cc: Li Zefan <lizf at cn.fujitsu.com>
> Cc: Rafael J. Wysocki <rjw at sisk.pl>
> Cc: linux-pm at lists.linux-foundation.org
> ---
>  kernel/cgroup_freezer.c |   21 +++++++++++++--------
>  1 files changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index da5e139..85f19cc 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -89,10 +89,10 @@ struct cgroup_subsys freezer_subsys;
>  
>  /* Locks taken and their ordering
>   * ------------------------------
> - * css_set_lock
>   * cgroup_mutex (AKA cgroup_lock)
> - * task->alloc_lock (AKA task_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
> @@ -100,33 +100,38 @@ struct cgroup_subsys freezer_subsys;
>   * freezer_create(), freezer_destroy():
>   * cgroup_mutex [ by cgroup core ]
>   *
> - * can_attach():
> - * cgroup_mutex
> + * freezer_can_attach():
> + * cgroup_mutex (held by caller of can_attach)
>   *
> - * cgroup_frozen():
> + * cgroup_freezing_or_frozen():
>   * task->alloc_lock (to get task's cgroup)
>   *
>   * freezer_fork() (preserving fork() performance means can't take cgroup_mutex):
> - * task->alloc_lock (to get task's cgroup)
>   * 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
> + *    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 (to prevent races with freeze_task())
> + *    task->alloc_lock (inside thaw_process(), prevents race with refrigerator())
>   *     sighand->siglock
>   */
>  static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
> 

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