linux-kernel - Re: rb tree hrtimer lockup bug (found by perf

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Date:	Tue, 18 Mar 2014 21:52:58 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: rb tree hrtimer lockup bug (found by perf_fuzzer)

On Tue, 18 Mar 2014, Vince Weaver wrote:
> On Tue, 18 Mar 2014, Thomas Gleixner wrote:
> 
> > On Tue, 18 Mar 2014, Vince Weaver wrote:
> > 
> > > 
> > > The perf_fuzzer can quickly cause a machine to lockup with an hrtimer 
> > > related rb tree related oops.  I've had a hard time debugging this in any 
> > > useful manner, but I can trigger it on both core2 and haswell test systems 
> > > on 3.14-rc7.
> > > 
> > > This involves making a large number of perf_event events of all types and 
> > > then forking a lot.
> > 
> > Can you enable debugobjects please? The should give us an hint what
> > corrupts the rbtree.
> 
> I enabled debugobjects and then said Y to most of the questions brought up 
> by make oldconfig but now the system crashes at boot:

> [    3.678040] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018                                                                        
> [    3.686776] IP: [<ffffffff8106d7a8>] get_next_timer_interrupt+0x168/0x250    

The back trace is not really helpful. Is there anything before that
BUG in dmesg?

Thanks,

	tglx

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