Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep
From: Sebastian Andrzej Siewior
Date: Wed Aug 28 2019 - 09:14:40 EST
On 2019-08-28 05:54:26 [-0700], Paul E. McKenney wrote:
> On Wed, Aug 28, 2019 at 11:27:39AM +0200, Sebastian Andrzej Siewior wrote:
> > On 2019-08-27 08:53:06 [-0700], Paul E. McKenney wrote:
> > > Am I understanding this correctly?
> > Everything perfect except that it is not lockdep complaining but the
> > WARN_ON_ONCE() in rcu_note_context_switch().
> This one, right?
> WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
> Another approach would be to change that WARN_ON_ONCE(). This fix might
> be too extreme, as it would suppress other issues:
> WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT_BASE) && !preempt && t->rcu_read_lock_nesting > 0);
> But maybe what is happening under the covers is that preempt is being
> set when sleeping on a spinlock. Is that the case?
I would like to keep that check and that is why we have:
| #if defined(CONFIG_PREEMPT_RT_FULL)
| sleeping_l = t->sleeping_lock;
| WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !sleeping_l);
in -RT and ->sleeping_lock is that counter that is incremented in
spin_lock(). And the only reason why sleeping_lock_inc() was used in the
patch was to disable _this_ warning.
> Thanx, Paul