Re: [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock

Paul E. McKenney
2020-04-21T15:43:14Z

On Tue, Apr 21, 2020 at 03:52:58PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 06, 2020 at 08:10:08PM +0800, Muchun Song wrote:
> > The walk_tg_tree_from() caller must hold rcu_lock,
>
> Not quite; with the RCU unification done 'recently' having preemption
> disabled is sufficient. AFAICT preemption is disabled.
>
> In fact; and I mentioned this to someone the other day, perhaps Joel; we
> can go and delete a whole bunch of rcu_read_lock() from the scheduler --
> basically undo all the work we did after RCU was split many years ago.

"If only I knew then what I know now..."

Then again, I suspect that we all have ample opportunity to use that
particular old phrase. ;-)

Thanx, Paul