On Mon, Sep 29, 2014 at 06:54:18PM +0200, Peter Zijlstra wrote: > On Mon, Sep 29, 2014 at 08:43:47PM +0400, Kirill Tkhai wrote: > > Thanks for your report. It looks like your fix is not enough, because > > we check for rcu_read_lock_sched_held() in dl_bw_of(). It still warns > > even if rcu_read_lock() is held. > > > > I used rcu_read_lock_sched_held() because we free root_domain using > > call_rcu_sched(). So, it's necessary to held rcu_read_lock_sched(), > > and my initial commit has this problem too. > > > > It looks like we should fix it in a way like this: > > > > [PATCH]sched: Use dl_bw_of() under rcu_read_lock_sched() > > > > rq->rd is freed using call_rcu_sched(), and it's accessed with preemption > > disabled in the most cases. > > > > So in other places we should use rcu_read_lock_sched() to access it to fit > > the scheme: > > > > rcu_read_lock_sched() or preempt_disable() <==> call_rcu_sched(). > > Hmm, sad that. I cannot remember why that is rcu_sched, I suspect > because we rely on it someplace but I cannot remember where. > > We could of course do a double take on that and use call_rcu after > call_rcu_sched(), such that either or both are sufficient. > > I would very much prefer not to add extra preempt_disable()s if > possible.
Ah wait, if we simply move that preempt_disable() inside the for_each_cpu() loop there's no harm done. Having them outside is painful though. -- 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/
