Subject: Re: [0/8] netpoll/bridge fixes

From: "Paul E. McKenney" <[email-masked]>
Date: Wed, 16 Jun 2010 16:02:49 -0700

On Tue, Jun 15, 2010 at 09:47:02PM -0700, David Miller wrote:
> From: Herbert Xu <[email-masked]>
> 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).
+
+	__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.