Re: sched_ext/lavd hard lockup in old call_rcu_tasks_generic needadjust path

[Paul E. McKenney]

On Thu, Jun 11, 2026 at 02:02:58PM +0100, Matt Fleming wrote:
> On Tue, Jun 09, 2026 at 04:23:23AM -0700, Paul E. McKenney wrote:
> > 
> > Does commenting out the 'call_rcu_tasks_generic+547' printk() avoid the
> > issue?  If so, that printk() might be deferred or some such.
> > 
> > "But if you cannot trust printk(), what *can* you trust?"  ;-)
> 
> I tried this and it still crashes so apparently not! I'll keep digging
> to find the real cause (it's somewhat cumbersome to reproduce this hard
> lockup).

If this code path is nevertheless involved, one thing that might speed
things up would be to do bursts of call_rcu_tasks() from lots of CPUs,
then avoid doing any call_rcu_tasks() for some time, then do a single
isolated call_rcu_tasks().  Or maybe you are already doing this.

							Thanx, Paul