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?
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
...)
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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