Li Zefan wrote:
> It is sufficient to check if @task is frozen, and no need to check if
> the original freezer is frozen.
hmm, a task being frozen does not mean that its freezer cgroup is
frozen. So the extra check seems valid but looking at the comment :
/*
* The call to cgroup_lock() in the freezer.state write method prevents
* a write to that file racing against an attach, and hence the
* can_attach() result will remain valid until the attach completes.
*/
static int freezer_can_attach(struct cgroup_subsys *ss,
how do we know that the task_freezer(task), which is not protected by
the cgroup_lock(), is not going to change its state to CGROUP_FROZEN
it looks racy.
C.
> Signed-off-by: Li Zefan <[EMAIL PROTECTED]>
> ---
> kernel/cgroup_freezer.c | 16 +++++++---------
> 1 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index 7f54d1c..6fadafe 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -162,9 +162,13 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
> struct task_struct *task)
> {
> struct freezer *freezer;
> - int retval;
>
> - /* Anything frozen can't move or be moved to/from */
> + /*
> + * Anything frozen can't move or be moved to/from.
> + *
> + * Since orig_freezer->state == FROZEN means that @task has been
> + * frozen, so it's sufficient to check the latter condition.
> + */
>
> if (is_task_frozen_enough(task))
> return -EBUSY;
> @@ -173,13 +177,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss,
> if (freezer->state == CGROUP_FROZEN)
> return -EBUSY;
>
> - retval = 0;
> - task_lock(task);
> - freezer = task_freezer(task);
> - if (freezer->state == CGROUP_FROZEN)
> - retval = -EBUSY;
> - task_unlock(task);
> - return retval;
> + return 0;
> }
>
> static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
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