From: Peter Zijlstra <peterz@infradead.org>
To: Dave Jones <davej@codemonkey.org.uk>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Stephane Eranian <eranian@gmail.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
Andi Kleen <andi@firstfloor.org>
Subject: Re: perf related lockdep bug
Date: Wed, 4 Nov 2015 11:50:10 +0100 [thread overview]
Message-ID: <20151104105010.GA11639@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20151104102800.GZ11639@twins.programming.kicks-ass.net>
On Wed, Nov 04, 2015 at 11:28:00AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 04, 2015 at 11:21:51AM +0100, Peter Zijlstra wrote:
>
> > The problem appears to be due to the new RCU expedited grace period
> > stuff, with rcu_read_unlock() now randomly trying to acquire locks it
> > previously didn't.
> >
> > Lemme go look at those rcu bits again..
>
> Paul, I think this is because of:
>
> 8203d6d0ee78 ("rcu: Use single-stage IPI algorithm for RCU expedited grace period")
>
> What happens is that the IPI comes in and tags any random
> rcu_read_unlock() with the special bit, which then goes on and takes
> locks.
>
> Now the problem is that we have scheduler activity inside this lock;
> the one reported lockdep seems easy enough to fix, see below.
>
> I'll got and see if there's more sites than can cause this.
*sigh* yes, there's gobs more. In fact the very first one I looked at:
rcu_dump_cpu_stacks()
raw_spin_lock_irqsave(&rnp->lock, flags);
dump_cpu_task()
pr_info()
That too will end up doing wakeups..
idem:
- print_other_cpu_stall()
- rcu_print_details_task_stall_rnp()
So just like you had to pull out all the rcu_gp_kthead_wake() calls from
under rnp->lock, so too must we pull out all implied wakeups, which very
much include printk().
next prev parent reply other threads:[~2015-11-04 10:50 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-04 5:17 perf related lockdep bug Dave Jones
2015-11-04 10:21 ` Peter Zijlstra
2015-11-04 10:28 ` Peter Zijlstra
2015-11-04 10:50 ` Peter Zijlstra [this message]
2015-11-04 13:48 ` Paul E. McKenney
2015-11-04 14:20 ` Peter Zijlstra
2015-11-04 15:34 ` Paul E. McKenney
2015-11-04 15:36 ` Peter Zijlstra
2015-11-04 15:51 ` Paul E. McKenney
2015-11-04 20:58 ` Andi Kleen
2015-11-05 0:55 ` Paul E. McKenney
2015-11-05 1:59 ` Paul E. McKenney
2015-11-05 2:46 ` Andi Kleen
2015-11-05 14:04 ` Paul E. McKenney
2015-11-11 13:29 ` Paul E. McKenney
2015-11-10 6:39 ` [tip:perf/urgent] perf: Disable IRQs across RCU RS CS that acquires scheduler lock tip-bot for Paul E. McKenney
2015-11-04 14:01 ` perf related lockdep bug Paul E. McKenney
2015-11-04 14:34 ` Peter Zijlstra
2015-11-05 1:57 ` Paul E. McKenney
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