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From: Scott Wood <swood@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Paul E . McKenney" <paulmck@linux.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Clark Williams <williams@redhat.com>
Subject: Re: [PATCH RT v3 5/5] rcutorture: Avoid problematic critical section nesting on RT
Date: Tue, 17 Sep 2019 11:32:11 -0500	[thread overview]
Message-ID: <b6b87f7acde58fcf0c172622eb9acef43a113ec4.camel@redhat.com> (raw)
In-Reply-To: <20190917145035.l6egzthsdzp7aipe@linutronix.de>

On Tue, 2019-09-17 at 16:50 +0200, Sebastian Andrzej Siewior wrote:
> On 2019-09-17 09:36:22 [-0500], Scott Wood wrote:
> > > On non-RT you can (but should not) use the counter part of the
> > > function
> > > in random order like:
> > > 	local_bh_disable();
> > > 	local_irq_disable();
> > > 	local_bh_enable();
> > > 	local_irq_enable();
> > 
> > Actually even non-RT will assert if you do local_bh_enable() with IRQs
> > disabled -- but the other combinations do work, and are used some places
> > via
> > spinlocks.  If they are used via direct calls to preempt_disable() or
> > local_irq_disable() (or via raw spinlocks), then that will not go away
> > on RT
> > and we'll have a problem.
> 
> lockdep_assert_irqs_enabled() is a nop with CONFIG_PROVE_LOCKING=N and
> RT breaks either way. 

Right, I meant a non-RT kernel with debug checks enabled.

> > > Since you _can_ use it in random order Paul wants to test that the
> > > random use of those function does not break RCU in any way. Since they
> > > can not be used on RT in random order it has been agreed that we keep
> > > the test for !RT but disable it on RT.
> > 
> > For now, yes.  Long term it would be good to keep track of when
> > preemption/irqs would be disabled on RT, even when running a non-RT
> > debug
> > kernel, and assert when bad things are done with it (assuming an RT-
> > capable
> > arch).  Besides detecting these fairly unusual patterns, it could also
> > detect earlier the much more common problem of nesting a non-raw
> > spinlock
> > inside a raw spinlock or other RT-atomic context.
> 
> you will be surprised but we have patches for that. We need first get
> rid of other "false positives" before plugging this in.

Nice!  Are the "false positives" real issues from components that are
currently blacklisted on RT, or something different?

-Scott



  reply	other threads:[~2019-09-17 16:32 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 16:57 [PATCH RT v3 0/5] RCU fixes Scott Wood
2019-09-11 16:57 ` [PATCH RT v3 1/5] rcu: Acquire RCU lock when disabling BHs Scott Wood
2019-09-12 22:09   ` Joel Fernandes
2019-09-17  7:44   ` Sebastian Andrzej Siewior
2019-09-17 14:06     ` Scott Wood
2019-09-17 14:42       ` Sebastian Andrzej Siewior
2019-09-17 16:12         ` Scott Wood
2019-09-23 16:41           ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 2/5] sched: Rename sleeping_lock to rt_invol_sleep Scott Wood
2019-09-17  7:52   ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 3/5] sched: migrate_dis/enable: Use rt_invol_sleep Scott Wood
2019-09-17  7:59   ` Sebastian Andrzej Siewior
2019-09-17 14:06     ` Scott Wood
2019-09-23 16:59       ` Scott Wood
2019-09-23 17:52         ` Sebastian Andrzej Siewior
2019-09-24 11:21           ` Sebastian Andrzej Siewior
2019-09-24 13:53             ` Scott Wood
2019-09-24 15:25               ` Sebastian Andrzej Siewior
2019-09-24 15:47                 ` Scott Wood
2019-09-24 16:05                   ` Sebastian Andrzej Siewior
2019-09-24 16:35                     ` Scott Wood
2019-10-04 16:45                       ` Sebastian Andrzej Siewior
2019-09-11 16:57 ` [PATCH RT v3 4/5] rcu: Disable use_softirq on PREEMPT_RT Scott Wood
2019-09-12 21:38   ` Joel Fernandes
2019-09-12 22:19     ` Joel Fernandes
2019-09-17  9:31     ` Sebastian Andrzej Siewior
2019-09-17 14:08   ` Scott Wood
2019-09-11 16:57 ` [PATCH RT v3 5/5] rcutorture: Avoid problematic critical section nesting on RT Scott Wood
2019-09-12 22:17   ` Joel Fernandes
2019-09-16 16:55     ` Scott Wood
2019-09-17 10:07       ` Sebastian Andrzej Siewior
2019-09-17 14:36         ` Scott Wood
2019-09-17 14:50           ` Sebastian Andrzej Siewior
2019-09-17 16:32             ` Scott Wood [this message]
2019-09-23 16:25               ` Sebastian Andrzej Siewior

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