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SubjectRe: Q: perf_event && event->owner
On 11/09, Peter Zijlstra wrote:
>
> I think you're right, how about something like this?

I need to read it with a fresh head ;)

At first glance,

> @@ -2254,6 +2249,12 @@ static int perf_release(struct inode *in
>
> file->private_data = NULL;
>
> + if (event->owner) {
> + mutex_lock(&event->owner->perf_event_mutex);
> + list_del_init(&event->owner_entry);
> + mutex_unlock(&event->owner->perf_event_mutex);
> + }

Agreed, it is better to do this in perf_release().

But, this can use the already freed task_struct, event->owner.

Either sys_perf_open() should do get_task_struct() like we currently
do, or perf_event_exit_task() should clear event->owner and then
perf_release() should do something like

rcu_read_lock();
owner = event->owner;
if (owner)
get_task_struct(owner);
rcu_read_unlock();

if (owner) {
mutex_lock(&event->owner->perf_event_mutex);
list_del_init(&event->owner_entry);
mutex_unlock(&event->owner->perf_event_mutex);
put_task_struct(owner);
}

Probably this can be simplified...

Oleg.



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