On Wed, Nov 28 2012, Tejun Heo wrote:
> Hello, Greg.
>
> On Wed, Nov 28, 2012 at 12:15:42PM -0800, Greg Thelen wrote:
>> @@ -4276,6 +4276,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
>> DEFINE_WAIT(wait);
>> struct cgroup_event *event, *tmp;
>> struct cgroup_subsys *ss;
>> + struct list_head tmp_list;
>
> LIST_HEAD(tmp_list);
>
>>
>> lockdep_assert_held(&d->d_inode->i_mutex);
>> lockdep_assert_held(&cgroup_mutex);
>> @@ -4330,16 +4331,20 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
>> /*
>> * Unregister events and notify userspace.
>> * Notify userspace about cgroup removing only after rmdir of cgroup
>> - * directory to avoid race between userspace and kernelspace
>> + * directory to avoid race between userspace and kernelspace. Use
>> + * a temporary list to avoid a deadlock with cgroup_event_wake(). Since
>> + * cgroup_event_wake() is called with the wait queue head locked,
>> + * remove_wait_queue() cannot be called while holding event_list_lock.
>> */
>> spin_lock(&cgrp->event_list_lock);
>> - list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) {
>> + list_replace_init(&cgrp->event_list, &tmp_list);
>
> list_splice_init();
>
> would be more conventional, I think.
I used list_replace_init() because it avoided unnecessary init of
tmp_list. But I have no objection to list_splice_init(). I'll repost
with list_splice_init().
>> + spin_unlock(&cgrp->event_list_lock);
>> + list_for_each_entry_safe(event, tmp, &tmp_list, list) {
>> list_del(&event->list);
>
> Maybe convert this to list_del_init() while at it?
I assume this isn't technically required, but defensive. Seems like we
should also convert the list_del(&event->list) in cgroup_event_wake()
for consistency. I'll send these in separate patch.
>> remove_wait_queue(event->wqh, &event->wait);
>> eventfd_signal(event->eventfd, 1);
>> schedule_work(&event->remove);
>> }
>> - spin_unlock(&cgrp->event_list_lock);
>
> Thanks.
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