Hi Peter, 2017-08-01 17:12 GMT+08:00 Peter Zijlstra <[email protected]>: > On Tue, Aug 01, 2017 at 04:57:43PM +0800, Yafang Shao wrote: >> > And how would that happen? We only call pick_next_entity(.curr=NULL) >> > when we _know_ cfs_rq->nr_running. >> >> It crashed my machine when I did hadoop test, and after I made this change >> it works now. >> On SMP system, cfs_rq->nr_running isn't protected well, although we _know_ >> cfs_rq->nr_running, >> but it is modified by other thread running on other CPU and the >> sched_entity is set NULL as well. >> Then this thread broken here as accessed the NULL pointer here. > > cfs_rq->nr_running should be protected by the rq->lock. If it is not, > something else is buggered.
Yes, I admit that something else is buggered, but unfortunately I haven't understood the scheduler deeply so can't find the root cause. But from my understanding, it is obviously a bug here as we can find that it may occurs that both 'se' and 'curr' are NULL. That's why I submit this patch to fix it.
