On Tue, Apr 13, 2010 at 05:13:06PM -0700, David Miller wrote:
> From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Date: Wed, 14 Apr 2010 02:02:27 +0200
>
> > I just have a guess though....
> > This seems to always happen from NMI path, and lockdep is disabled on NMI.
> > I suspect the lock_acquire() performed by rcu_read_lock() is just ignored
> > and then the rcu_read_lock_held() check has the wrong result...
>
> Yeah, I bet that's it too.
>
> lock_is_held() can't return anything meaningful while lockdep is
> disabled, which it is during NMIs.
Ah! So I just need to add a "current->lockdep_recursion"
check to debug_lockdep_rcu_enabled(). And move the function to
kernel/rcutree_plugin.h to avoid #include hell.
See below for (untested) patch.
Thanx, Paul
------------------------------------------------------------------------
include/linux/rcupdate.h | 5 +----
kernel/rcutree_plugin.h | 11 +++++++++++
2 files changed, 12 insertions(+), 4 deletions(-)
commit 304d8da6cd791a81ce3164f867e1b3ef4f9af1d1
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
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.
Reported-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Reported-by: David Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
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/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 79b53bd..2169abe 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1067,3 +1067,14 @@ static void rcu_needs_cpu_flush(void)
}
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int debug_lockdep_rcu_enabled(void)
+{
+ return likely(rcu_scheduler_active &&
+ debug_locks &&
+ current->lockdep_recursion == 0);
+}
+
+#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
--
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