On Mon, Jun 23, 2014 at 02:52:18PM +0400, Kirill Tkhai wrote:
> > Then again, I suppose anything without rq->lock can and will miss tasks.
>
> If we use rq->lock it's possible to move check_for_tasks() to
> kernel/sched/core.c.
>
> And we can leave TASK_RUNNING check for waking tasks. Maybe something like
> this?
>
> static inline void check_for_tasks(int dead_cpu)
> {
> struct task_struct *g, *p;
> struct rq *rq = cpu_rq(dead_cpu);
>
> read_lock_irq(&tasklist_lock);
> raw_spin_lock(&rq->lock)
>
> do_each_thread(g, p) {
> if (!p->on_rq && p->state != TASK_RUNNING)
> continue;
> if (task_cpu(p) != dead_cpu)
> continue;
>
> pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
> p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
> } while_each_thread(g, p);
>
> raw_spin_unlock(&rq->lock)
> read_unlock_irq(&tasklist_lock);
> }
>
> It still does not give a 100% guarantee... Should we take p->pi_lock for
> every task?
seeing how rq->lock nests inside of ->pi_lock that's going to be
somewhat icky.
I think we can live with a false negative, given how much people run
this nonsense it'll trigger eventually.
False positives would be bad though :-)
So I think we can keep your original (lock-free) proposal.
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