Hello, guys. On Wed, Dec 21, 2011 at 03:44:14AM -0800, tip-bot for Daisuke Nishimura wrote: > sched: Fix cgroup movement of forking process > > There is a small race between task_fork_fair() and sched_move_task(), > which is trying to move the parent. > > task_fork_fair() sched_move_task() > --------------------------------+--------------------------------- > cfs_rq = task_cfs_rq(current) > -> cfs_rq is the "old" one. > curr = cfs_rq->curr > -> curr is set to the parent. > task_rq_lock() > dequeue_task() > ->parent.se.vruntime -= (old)cfs_rq->min_vruntime > enqueue_task() > ->parent.se.vruntime += (new)cfs_rq->min_vruntime > task_rq_unlock() > raw_spin_lock_irqsave(rq->lock) > se->vruntime = curr->vruntime > -> vruntime of the child is set to that of the parent > which has already been updated by sched_move_task(). > se->vruntime -= (old)cfs_rq->min_vruntime. > raw_spin_unlock_irqrestore(rq->lock) > > As a result, vruntime of the child becomes far bigger than expected, > if (new)cfs_rq->min_vruntime >> (old)cfs_rq->min_vruntime. > > This patch fixes this problem by setting "cfs_rq" and "curr" after > holding the rq->lock. The race shouldn't happen with threadgroup locking scheduled to be merged for the coming merge window. sched_fork() and cgroup migration become exclusive and won't happen concurrently. Would still make sense for -stable tho. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|