On Sat, Oct 18, 2014 at 12:33:27PM +0400, Kirill Tkhai wrote: > How about this? > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index b78280c..d46427e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1165,7 +1165,21 @@ static void task_numa_compare(struct task_numa_env > *env, > > rcu_read_lock(); > cur = ACCESS_ONCE(dst_rq->curr); > - if (cur->pid == 0) /* idle */ > + /* > + * No need to move the exiting task, and this ensures that ->curr > + * wasn't reaped and thus get_task_struct() in task_numa_assign() > + * is safe; note that rcu_read_lock() can't protect from the final > + * put_task_struct() after the last schedule(). > + */ > + if (is_idle_task(cur) || (cur->flags & PF_EXITING)) > + cur = NULL; > + /* > + * Check once again to be sure curr is still on dst_rq. Even if > + * it points on a new task, which is using the memory of freed > + * cur, it's OK, because we've locked RCU before > + * delayed_put_task_struct() callback is called to put its struct. > + */ > + if (cur != ACCESS_ONCE(dst_rq->curr)) > cur = NULL; > > /*
So you worry about the refcount doing 0->1 ? In which case the above is still wrong and we should be using atomic_inc_not_zero() in order to acquire the reference count. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
