From: "Paul E. McKenney" <paulmck@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Scott Wood <swood@redhat.com>,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Clark Williams <williams@redhat.com>
Subject: Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep
Date: Wed, 28 Aug 2019 08:50:28 -0700 [thread overview]
Message-ID: <20190828155028.GP26530@linux.ibm.com> (raw)
In-Reply-To: <20190828131433.3gi4debho5zc7hgc@linutronix.de>
On Wed, Aug 28, 2019 at 03:14:33PM +0200, Sebastian Andrzej Siewior wrote:
> 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;
> | #endif
> | 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.
Very good! I would prefer an (one-line) access function to keep the
number of #if uses down to dull roar, but other than that, looks good!
(Yeah, I know, this is tree_preempt.h, but still...)
Thanx, Paul
next prev parent reply other threads:[~2019-08-28 15:51 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 23:19 [PATCH RT v2 0/3] RCU fixes Scott Wood
2019-08-21 23:19 ` [PATCH RT v2 1/3] rcu: Acquire RCU lock when disabling BHs Scott Wood
2019-08-21 23:33 ` Paul E. McKenney
2019-08-22 13:39 ` Joel Fernandes
2019-08-22 15:27 ` Paul E. McKenney
2019-08-23 1:50 ` Joel Fernandes
2019-08-23 2:11 ` Paul E. McKenney
2019-08-23 3:23 ` Scott Wood
2019-08-23 12:30 ` Paul E. McKenney
2019-08-23 16:17 ` Sebastian Andrzej Siewior
2019-08-23 19:46 ` Scott Wood
2019-08-26 15:59 ` Sebastian Andrzej Siewior
2019-08-26 23:21 ` Scott Wood
2019-08-23 2:36 ` Scott Wood
2019-08-23 2:54 ` Paul E. McKenney
2019-08-21 23:19 ` [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Scott Wood
2019-08-21 23:35 ` Paul E. McKenney
2019-08-23 1:21 ` Scott Wood
2019-08-23 16:20 ` Sebastian Andrzej Siewior
2019-08-23 19:28 ` Scott Wood
2019-08-24 3:10 ` Joel Fernandes
2019-08-26 15:25 ` Sebastian Andrzej Siewior
2019-08-26 16:29 ` Paul E. McKenney
2019-08-26 17:49 ` Scott Wood
2019-08-26 18:12 ` Paul E. McKenney
2019-08-27 9:23 ` Sebastian Andrzej Siewior
2019-08-27 13:08 ` Joel Fernandes
2019-08-27 15:58 ` Paul E. McKenney
2019-08-27 16:06 ` Joel Fernandes
2019-08-27 15:53 ` Paul E. McKenney
2019-08-28 9:27 ` Sebastian Andrzej Siewior
2019-08-28 12:54 ` Paul E. McKenney
2019-08-28 13:14 ` Sebastian Andrzej Siewior
2019-08-28 13:59 ` Joel Fernandes
2019-08-28 15:51 ` Paul E. McKenney
2019-08-28 15:50 ` Paul E. McKenney [this message]
2019-08-21 23:19 ` [PATCH RT v2 3/3] rcu: Disable use_softirq on PREEMPT_RT Scott Wood
2019-08-21 23:40 ` Paul E. McKenney
2019-08-23 16:32 ` Sebastian Andrzej Siewior
2019-08-22 13:59 ` Joel Fernandes
2019-08-22 15:29 ` Paul E. McKenney
2019-08-22 19:31 ` Scott Wood
2019-08-23 0:52 ` Joel Fernandes
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