linux-kernel - Re: Fw: RCU boot debug patch

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Message-ID: <CAAVPGOMQ5AWDVb0Cce2EBM84Q-jEG1_TzQn=6PSegn-thEe9TQ@mail.gmail.com>
Date:	Thu, 28 Jul 2011 20:56:25 +0100
From:	Julie Sullivan <kernelmail.jms@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Kyle Moffett <kyle@...fetthome.net>,
	RKK <kulkarni.ravi4@...il.com>, linux-kernel@...r.kernel.org,
	cmm@...ibm.com
Subject: Re: Fw: RCU boot debug patch

On Thu, Jul 28, 2011 at 1:02 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Jul 27, 2011 at 07:56:10PM -0400, Kyle Moffett wrote:
>> On Wed, Jul 27, 2011 at 17:47,  <kernelmail.jms@...il.com> wrote:
>> >>A debug patch to verify if there is RCU callbacks before the rcu scheduler is active
>> > So something gives me the impression we may have an answer somewhere in this dmesg for this... ;-)
>> >
>> > Here is my dmesg (the whole thing):
>> >
>> > function free_object_rcu
>> > [    0.166707] RCU scheduler is not active yet, Calling _call_rcu() with this function free_object_rcu
>> > [....thousands of lines snipped...]
>> > [    0.225223] RCU scheduler is not active yet, Calling _call_rcu() with this function free_object_rcu
>
> Thank you, Julie!
>
>> Well this looks an awful lot like a smoking gun here...
>>
>> I can only find one function called "free_object_rcu", and it seems to be a
>> static function in mm/kmemleak.c, and it certainly does this:
>>    call_rcu(&object->rcu, free_object_rcu);
>>
>> So the next question for you would be:  Do all the messages go away if you
>> turn off the kmemleak config option?
>
> Hello, Kyle,
>
> This is not at all showing a problem in free_object_rcu(), but rather
> as a sanity-check for a shoot-from-the-hip fix.  The fix seemed to
> work, but my paranoia dictated that I check that my guess was correct.
> Which it appears that it was.
>
> So again, these messages do not indicate a problem in free_object_rcu().
>
>                                                        Thanx, Paul
>

Let me know if you want me to test anything else. :-)

Cheers
Julie
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