Hi,
Starring at some parts of cgroups, I have a few questions:
- Is cgroup_enable_task_cg_list()'s while_each_thread() safe
against concurrent exec()? The leader may change in de_thread()
and invalidate the test done in while_each_thread().
- do_each_thread() also needs RCU and cgroup_enable_task_cg_list()
seems to remind it. But it seems there is at least one caller that
doesn't call rcu_read_lock(): update_cpu_mask() -> update_tasks_cpumask() -> cgroup_scan_tasks()
- By the time we call cgroup_post_fork(), it is ready to be woken up
and usable by the scheduler. I was thinking about a possible race
where somebody kills the child just before we call cgroup_post_fork()
and then it ends up calling cgroup_exit(). In this case should we perhaps
check for PF_EXITING. Of course I'm talking about a race that will certainly
never happen.
If I'm mistaken and the task can not exit concurrently, probably we don't need
the task_lock() there.
- Is the check for use_task_css_set_links in cgroup_post_fork() safe? given
it is checked outside css_set_lock?
Imagine this:
CPU 0 CPU 1
---- -----
cgroup_enable_task_cg() {
uset_tasks_css_set_links = 1
for_each_thread() {
add tasks in the list
}
}
do_fork() {
cgroup_post_fork() {
use_tasks_css_set_links appears
to be equal to 0 due to write/read
not flushed. New task won't
appear to the list.
- Is the read_lock() in cgroup_attach_proc() still necessary? It was added to protect
against exec() but now I think it is useless. rcu_read_lock() would be necessary to protect
against group_entry removal though I think.
Thanks.
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