Re: [ltt-dev] lttctl locks up with RT Linux

From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: jpaul@gdrs.com
Cc: paulmck@linux.vnet.ibm.com, ltt-dev@lists.casi.polymtl.ca,
	linux-rt-users@vger.kernel.org
Subject: Re: [ltt-dev] lttctl locks up with RT Linux
Date: Fri, 14 May 2010 10:56:55 -0400	[thread overview]
Message-ID: <20100514145655.GA9145@Krystal> (raw)
In-Reply-To: <A47866F933DF804684068A24BF04A9730862A80B@gdrs-exchange.gdrs.com>

Ah! I think I brought debugging to a whole new level here, including
developer interaction in the bissection. ;)

Thanks for the reports, they have been very useful to re-enable LTTng
for -rt kernels,

Mathieu

* jpaul@gdrs.com (jpaul@gdrs.com) wrote:
> Thanks Mathieu.  This was my fault .. I couldn't apply your patch
> (kept getting failures on hunks 2-8 for some reason) so I hand patched
> the file and in doing so, transposed a rcu unlock with an rcu lock
> (just as you suspected). So, after correcting that, all is well and
> I'm able to perform tracing under 2.6.33.2 RT.
> 
> Thanks Much!
> 
> JP
> 
> 
> -----Original Message-----
> From: Mathieu Desnoyers [mailto:compudj@krystal.dyndns.org]
> Sent: Thu 5/13/2010 2:23 PM
> To: John P. Paul
> Cc: ltt-dev@lists.casi.polymtl.ca; paulmck@linux.vnet.ibm.com; linux-rt-users@vger.kernel.org
> Subject: Re: [ltt-dev] lttctl locks up with RT Linux
>  
> Please double-check that you applied the last patch correctly. I tried
> building a lttng-enabled -rt tree here (x86 64 box), and it works (I can
> start/stop tracing and see the trace in lttv).
> 
> Note that I simply discarded the conflicting instrumentation patches for
> this quick test.
> 
> I'm pretty sure an error could have been inserted in async_wakeup()
> within ltt-tracer.c. Can you paste the code you have ?
> 
> Unbalanced rcu read lock/unlock could be causing this.
> 
> Thanks,
> 
> Mathieu
> 
> * jpaul@gdrs.com (jpaul@gdrs.com) wrote:
> > Turning off CONFIG_RCU_CPU_STALL_DETECTOR does not solve the issue with starting up "lttctl -C" ... that call never returns. I'm no longer getting the stack dumps in /var/log/messages and I still have to hard reboot the system as soft reboot doesn't work.
> > 
> > JP
> 
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com