From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Scott Wood <swood@redhat.com>
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 16:50:35 +0200 [thread overview]
Message-ID: <20190917145035.l6egzthsdzp7aipe@linutronix.de> (raw)
In-Reply-To: <26dbecfee2c02456ddfda3647df1bcd56d9cc520.camel@redhat.com>
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.
> > 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.
> -Scott
Sebastian
next prev parent reply other threads:[~2019-09-17 14:50 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 [this message]
2019-09-17 16:32 ` Scott Wood
2019-09-23 16:25 ` Sebastian Andrzej Siewior
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