[Devel] Re: [ckrm-tech] [PATCH 1/7] containers (V7): Generic container system abstracted from cpusets code

[Paul Jackson]

> IMO, we need to use task_lock() in container_exit() to avoid this race.
> 
> (I think this race already exists in mainline cpuset.c?)
> 
> P.S : cpuset.c checks for PF_EXITING twice in attach_task(), while this
> patch seems to be checking only once. Is that fine?

I think the cpuset code is ok, because, as you note, it locks the task,
picks off the cpuset pointer, and then checks a second time that the
task still does not have PF_EXITING set:

In the kernel/cpuset.c code for attach_task():

        task_lock(tsk);
        oldcs = tsk->cpuset;
        /*
         * After getting 'oldcs' cpuset ptr, be sure still not exiting.
         * If 'oldcs' might be the top_cpuset due to the_top_cpuset_hack
         * then fail this attach_task(), to avoid breaking top_cpuset.count.
         */
        if (tsk->flags & PF_EXITING) {
                task_unlock(tsk);
                mutex_unlock(&callback_mutex);
                put_task_struct(tsk);
                return -ESRCH;
        }

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