linux-kernel - Re: [ltt-dev] LTTng0.158 Linux-2629-RT kernel BUG: sleeping function called from invalid context at kernel/rtmutex.c:685

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Date:	Wed, 17 Feb 2010 16:06:28 +0530
From:	naresh kamboju <naresh.kernel@...il.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	ltt-dev@...ts.casi.polymtl.ca, linux-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-rt-users@...r.kernel.org
Subject: Re: [ltt-dev] LTTng0.158 Linux-2629-RT kernel BUG: sleeping function 
	called from invalid context at kernel/rtmutex.c:685

Hi,

On Tue, Feb 16, 2010 at 10:35 PM, Mathieu Desnoyers
<compudj@...stal.dyndns.org> wrote:
> * Thomas Gleixner (tglx@...utronix.de) wrote:
>> On Tue, 16 Feb 2010, Mathieu Desnoyers wrote:
>> > > The function is called from an IPI. That's a LTTNG problem, not a RT one.

yes. it's seems be a LTTng0.158 problem.
I have tested with below combinations.

2.6.29                        ->no issues
2.6.29+LTTng0.100      ->no issues
2.6.29+LTTng0.158     ->no issues

2.6.29-RT                   ->no issues
2.6.29-RT+LTTng0.100 ->no issues
2.6.29-RT+LTTng0.158 ->BUG reported.

>> >
>> > I use del_timer in IPI to delete lttng per-cpu timers on all CPUs. I
>> > have to do this because timers created with add_timer_on are documented
>> > to be incompatible with del_timer_sync():
>> >
>> >  * Synchronization rules: Callers must prevent restarting of the timer,
>> >  * otherwise this function is meaningless. It must not be called from
>> >  * interrupt contexts. The caller must not hold locks which would prevent
>> >  * completion of the timer's handler. The timer's handler must not call
>> >  * add_timer_on(). Upon exit the timer is not queued and the handler is
>> >  * not running on any CPU.
>>
>> Errm. The documentation says:
>>
>>       "The timer's handler must not call add_timer_on()."
>>
>> It's not talking about a timer which was initialized with
>> add_timer_on().
>>
>>  And your per cpu timer handlers have no requirement to call
>> add_timer_on() simply because add/mod_timer() is requeueing the timer
>> on the same cpu on which the handler runs.
>>
>> So the IPI is just a solution for a non existing problem.
>
> Oh, right. Thanks for the explanation. I'll look into moving LTTng to a
> saner del_timer_sync() scheme to delete the timers.

Could you give more info regarding, what kind of changes we can work on.
let me also work around on it.

Best regards,
Naresh Kamboju

>
> Thanks,
>
> Mathieu
>
>>
>> Thanks,
>>
>>       tglx
>>
>
> --
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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