netdev - Re: [0/8] netpoll/bridge fixes

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Message-ID: <20100617101830.GJ7912@redhat.com>
Date:	Thu, 17 Jun 2010 13:18:30 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	David Miller <davem@...emloft.net>, herbert@...dor.hengli.com.au,
	eric.dumazet@...il.com, shemminger@...tta.com, frzhang@...hat.com,
	netdev@...r.kernel.org, amwang@...hat.com, mpm@...enic.com
Subject: Re: [0/8] netpoll/bridge fixes

On Wed, Jun 16, 2010 at 04:02:49PM -0700, Paul E. McKenney wrote:
> On Tue, Jun 15, 2010 at 09:47:02PM -0700, David Miller wrote:
> > From: Herbert Xu <herbert@...dor.apana.org.au>
> > Date: Wed, 16 Jun 2010 13:33:36 +1000
> > 
> > > On Wed, Jun 16, 2010 at 05:03:20AM +0200, Eric Dumazet wrote:
> > >>
> > >> I wonder how these patches were tested, Herbert ?
> > > 
> > > You know, not everyone enables RCU debugging...
> > 
> > Even though I'm as guilty as you, I have to agree with Eric that
> > especially us core folks should be running with the various lock
> > debugging options on all the time.
> > 
> > Maybe someone should add the RCU debugging config option to
> > Documentation/SubmitChecklist :-)
> 
> How about the following added to Documentation/RCU/checklist.txt?
> 
> The first is in mainline, the second partly there, and the third
> is still languishing in my tree.  I did manage to remove a dependency
> on other maintainers, so things will hopefully move a bit faster.
> 
> 							Thanx, Paul
> 
> diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
> index 790d1a8..c7c6788 100644
> --- a/Documentation/RCU/checklist.txt
> +++ b/Documentation/RCU/checklist.txt
> @@ -365,3 +365,26 @@ over a rather long period of time, but improvements are always welcome!
>  	and the compiler to freely reorder code into and out of RCU
>  	read-side critical sections.  It is the responsibility of the
>  	RCU update-side primitives to deal with this.
> +
> +17.	Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and
> +	the __rcu sparse checks to validate your RCU code.  These
> +	can help find problems as follows:
> +
> +	CONFIG_PROVE_RCU: check that accesses to RCU-protected data
> +		structures are carried out under the proper RCU
> +		read-side critical section, while holding the right
> +		combination of locks, or whatever other conditions
> +		are appropriate.
> +
> +	CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the
> +		same object to call_rcu() (or friends) before an RCU
> +		grace period has elapsed since the last time that you
> +		passed that same object to call_rcu() (or friends).
> +

Cool, will this also work with synchronize etc?

> +	__rcu sparse checks: tag the pointer to the RCU-protected data
> +		structure with __rcu, and sparse will warn you if you
> +		access that pointer without the services of one of the
> +		variants of rcu_dereference().
> +
> +	These debugging aids can help you find problems that are
> +	otherwise extremely difficult to spot.
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