Messages in this thread Patch in this message | | | Date | Tue, 21 Oct 2008 09:32:50 +0200 | From | Cedric Le Goater <> | Subject | Re: [PATCH 2/4] freezer_cg: remove redundant check in freezer_can_attach() |
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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 <lizf@cn.fujitsu.com> > --- > 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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