From: John Keeping <john@metanate.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
linux-rt-users@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Lockdep splat from destroy_workqueue() with RT_PREEMPT_FULL
Date: Thu, 8 Dec 2016 16:25:44 +0000 [thread overview]
Message-ID: <20161208162544.1909caf2.john@metanate.com> (raw)
In-Reply-To: <20161208133306.254xkj2d4a2c24yr@linutronix.de>
Hi Sebastian,
On Thu, 8 Dec 2016 14:33:06 +0100, Sebastian Andrzej Siewior wrote:
> On 2016-12-08 12:20:28 [+0000], John Keeping wrote:
> > I am seeing the following splat when stopping btattach on v4.4.30-rt41
> > with PREEMPT_RT_FULL with lockdep and slub_debug.
> >
> > The bad unlock balance seems to just be an effect of the lock having
> > been overwritten with POISON_FREE, the real issue is that
> > put_pwq_unlocked() is not resuming and unlocking the pool before the RCU
> > work scheduled indirectly by put_pwq() has completed.
>
> can you reproduce this? If so, is this patch helping?
Yes, I am able to reproduce it reasonably reliably, or at least I *was*
able to: since applying the patch below I haven't seen it fail at all,
so consider the patch:
Tested-by: John Keeping <john@metanate.com>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1135,9 +1135,11 @@ static void put_pwq_unlocked(struct pool_workqueue *pwq)
> * As both pwqs and pools are RCU protected, the
> * following lock operations are safe.
> */
> + rcu_read_lock();
> local_spin_lock_irq(pendingb_lock, &pwq->pool->lock);
> put_pwq(pwq);
> local_spin_unlock_irq(pendingb_lock, &pwq->pool->lock);
> + rcu_read_unlock();
> }
> }
John
prev parent reply other threads:[~2016-12-08 16:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 12:20 Lockdep splat from destroy_workqueue() with RT_PREEMPT_FULL John Keeping
2016-12-08 13:33 ` Sebastian Andrzej Siewior
2016-12-08 16:25 ` John Keeping [this message]
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