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Subject[RFC][PATCH 3/6] lockdep: rcu_dereference() vs preempt_disable()
Don't warn when preemption is disabled using preempt_disable()

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/preempt.h | 19 +++++++++++--------
kernel/sched.c | 14 ++++++++++----
lib/Kconfig.debug | 1 +
3 files changed, 22 insertions(+), 12 deletions(-)
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -3396,7 +3396,7 @@ void scheduler_tick(void)

#if defined(CONFIG_PREEMPT) && defined(CONFIG_DEBUG_PREEMPT)

-void fastcall add_preempt_count(int val)
+void fastcall __add_preempt_count(int val, int exp)
{
/*
* Underflow?
@@ -3409,10 +3409,13 @@ void fastcall add_preempt_count(int val)
*/
DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
PREEMPT_MASK - 10);
+
+ if (exp)
+ rcu_read_acquire();
}
-EXPORT_SYMBOL(add_preempt_count);
+EXPORT_SYMBOL(__add_preempt_count);

-void fastcall sub_preempt_count(int val)
+void fastcall __sub_preempt_count(int val, int exp)
{
/*
* Underflow?
@@ -3427,8 +3430,11 @@ void fastcall sub_preempt_count(int val)
return;

preempt_count() -= val;
+
+ if (exp)
+ rcu_read_release();
}
-EXPORT_SYMBOL(sub_preempt_count);
+EXPORT_SYMBOL(__sub_preempt_count);

#endif

Index: linux-2.6/include/linux/preempt.h
===================================================================
--- linux-2.6.orig/include/linux/preempt.h
+++ linux-2.6/include/linux/preempt.h
@@ -11,15 +11,18 @@
#include <linux/list.h>

#ifdef CONFIG_DEBUG_PREEMPT
- extern void fastcall add_preempt_count(int val);
- extern void fastcall sub_preempt_count(int val);
+ extern void fastcall __add_preempt_count(int val, int exp);
+ extern void fastcall __sub_preempt_count(int val, int exp);
#else
-# define add_preempt_count(val) do { preempt_count() += (val); } while (0)
-# define sub_preempt_count(val) do { preempt_count() -= (val); } while (0)
+# define __add_preempt_count(val, exp) do { preempt_count() += (val); } while (0)
+# define __sub_preempt_count(val, exp) do { preempt_count() -= (val); } while (0)
#endif

-#define inc_preempt_count() add_preempt_count(1)
-#define dec_preempt_count() sub_preempt_count(1)
+#define add_preempt_count(val) __add_preempt_count(val, 0);
+#define sub_preempt_count(val) __sub_preempt_count(val, 0);
+
+#define inc_preempt_count() __add_preempt_count(1, 0)
+#define dec_preempt_count() __sub_preempt_count(1, 0)

#define preempt_count() (current_thread_info()->preempt_count)

@@ -29,14 +32,14 @@ asmlinkage void preempt_schedule(void);

#define preempt_disable() \
do { \
- inc_preempt_count(); \
+ __add_preempt_count(1, 1); \
barrier(); \
} while (0)

#define preempt_enable_no_resched() \
do { \
barrier(); \
- dec_preempt_count(); \
+ __sub_preempt_count(1, 1); \
} while (0)

#define preempt_check_resched() \
Index: linux-2.6/lib/Kconfig.debug
===================================================================
--- linux-2.6.orig/lib/Kconfig.debug
+++ linux-2.6/lib/Kconfig.debug
@@ -237,6 +237,7 @@ config DEBUG_SEMAPHORE
config DEBUG_LOCK_ALLOC
bool "Lock debugging: detect incorrect freeing of live locks"
depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
+ select DEBUG_PREEMPT
select DEBUG_SPINLOCK
select DEBUG_MUTEXES
select LOCKDEP
--

-
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