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

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Message-ID: <20110728000254.GB2318@linux.vnet.ibm.com>
Date:	Wed, 27 Jul 2011 17:02:54 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Kyle Moffett <kyle@...fetthome.net>
Cc:	kernelmail.jms@...il.com, RKK <kulkarni.ravi4@...il.com>,
	linux-kernel@...r.kernel.org, cmm@...ibm.com
Subject: Re: Fw: RCU boot debug patch

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
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