linux-kernel - Re: Weird rcu lockdep warning

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Date:	Wed, 14 Apr 2010 21:24:26 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	David Miller <davem@...emloft.net>, a.p.zijlstra@...llo.nl,
	mingo@...e.hu, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Weird rcu lockdep warning

On Wed, Apr 14, 2010 at 09:00:57AM -0700, Paul E. McKenney wrote:
> On Wed, Apr 14, 2010 at 05:51:11PM +0200, Frederic Weisbecker wrote:

[ . . .]

> > Note I just tested the patch the previous one and it looks fine now.
> > You can then safely consider the "general idea" fixes the problem :)
> 
> Thank you, Frederic!!!

And here is what I hope is the official fix.

Could you please test it?

							Thanx, Paul

------------------------------------------------------------------------

commit 9be39c445a41e458d53cf9a57d25dbfa4b74c970
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Tue Apr 13 18:45:51 2010 -0700

    rcu: Make RCU lockdep check the lockdep_recursion variable
    
    The lockdep facility temporarily disables lockdep checking by incrementing
    the current->lockdep_recursion variable.  Such disabling happens in NMIs
    and in other situations where lockdep might expect to recurse on itself.
    This patch therefore checks current->lockdep_recursion, disabling RCU
    lockdep splats when this variable is non-zero.  In addition, this patch
    removes the "likely()", as suggested by Lai Jiangshan.
    
    Reported-by: Frederic Weisbecker <fweisbec@...il.com>
    Reported-by: David Miller <davem@...emloft.net>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 9f1ddfe..07db2fe 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -101,10 +101,7 @@ extern struct lockdep_map rcu_sched_lock_map;
 # define rcu_read_release_sched() \
 		lock_release(&rcu_sched_lock_map, 1, _THIS_IP_)
 
-static inline int debug_lockdep_rcu_enabled(void)
-{
-	return likely(rcu_scheduler_active && debug_locks);
-}
+extern int debug_lockdep_rcu_enabled(void);
 
 /**
  * rcu_read_lock_held - might we be in RCU read-side critical section?
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 63fe254..03a7ea1 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -69,6 +69,13 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
+int debug_lockdep_rcu_enabled(void)
+{
+	return rcu_scheduler_active && debug_locks &&
+	       current->lockdep_recursion == 0;
+}
+EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
+
 /**
  * rcu_read_lock_bh_held - might we be in RCU-bh read-side critical section?
  *
--
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