On Fri, 2006-08-04 at 19:56 -0700, Paul Menage wrote:
> What's the recommended safe way to access current->res_group (or even
> an arbitrary task->res_group) without racing against a concurrent
> set_res_group() call from a different process?
I simplified some amount of locking in the last post. May be we
overlooked some situations.
Will look into it.
>
> For example, when calling numtasks_allow_fork(current->res_group) in
> numtasks, I don't see anything that guarantees that current will
> remain in the same res_group, or even that the res_group will persist
> for the lifetime of the call. (OK, so numtasks_allow_fork() isn't
> exactly a very long function call, but it's the principle that counts
> ...)
I totally agree.
>
> How about using task->alloc_lock to protect task->res_group? So all
> manipulation would either have to be done inside task->alloc_lock, or
> else would need to use a function such as:
>
> struct resource_group *task_get_res_group(struct task_struct *task) {
> struct resource_group *res;
> lock_task(task);
> res = task->res_group;
> if (res) kref_get(&res->ref);
> unlock_task(task);
> return res;
> }
>
> An alternative (more efficient but more complex) approach would be to use RCU.
>
> Paul
>
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