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Subject[PATCH v2] check spinlock_t/rwlock_t argument type on non-SMP builds
Date
When writing code for UP without CONFIG_DEBUG_SPINLOCK it's easy to get
the first argument to the spinlock/rwlock functions wrong. This is
because the parameter is not actually used in this configuration.

Typically you will only find out it's wrong
* by rebuilding with CONFIG_SMP or CONFIG_DEBUG_SPINLOCK
* after you've submitted your beautiful patch series.

The first means a long wait, and the latter is a bit late.

Change the intermediate macros into inline functions.

Signed-off-by: David Kilroy <kilroyd@googlemail.com>
Cc: Ingo Molnar <mingo@elte.hu>
---

The previous version of this patch achieved the typechecking by
explicitly calling typecheck() within the macros. This version, at the
behest of Ingo, turns the macros into proper C functions. One benefit of
this is that the compiler no longer complains about how net/ipv4/route.c
passes NULL into spinlock_xx()

I've made the functions static inline, so there should be minimal impact
on generated code (assuming the compiler is listening). I haven't done
any comparisons yet.

In an allyesconfig build, compiler warnings are unchanged. One
side-effect of this is that sparse (with -Wcontext) reports certain
locking errors against spinlock_api_up.h instead of the file containing
the function doing the spinlock call. For example:

CHECK kernel/rtmutex.c
kernel/rtmutex.c:149:5: warning: symbol 'max_lock_depth' was not declared. Should it be static?
kernel/rtmutex.c:291:2: warning: context imbalance in 'rt_mutex_adjust_prio_chain' - different lock contexts for basic block
kernel/rtmutex.c:675:3: warning: context imbalance in '__rt_mutex_slowlock' - unexpected unlock
kernel/rtmutex.c:1029:5: warning: context imbalance in 'rt_mutex_start_proxy_lock' - wrong count at exit
CC kernel/rtmutex.o

becomes...

CHECK kernel/rtmutex.c
kernel/rtmutex.c:149:5: warning: symbol 'max_lock_depth' was not declared. Should it be static?
kernel/rtmutex.c:291:2: warning: context imbalance in 'rt_mutex_adjust_prio_chain' - different lock contexts for basic block
include/linux/spinlock_api_up.h:103:3: warning: context imbalance in '__rt_mutex_slowlock' - unexpected unlock
kernel/rtmutex.c:1029:5: warning: context imbalance in 'rt_mutex_start_proxy_lock' - wrong count at exit
CC kernel/rtmutex.o

This might just be my version of sparse. I tried adding the __acquires()
tag to the inline functions, but sparse didn't behave any differently.

Ingo - is this what you were thinking of?


Thanks,

Dave.

---
include/linux/spinlock.h | 6 +-
include/linux/spinlock_api_up.h | 118 +++++++++++++++++++++++++++++----------
2 files changed, 92 insertions(+), 32 deletions(-)

diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
index 252b245..6462de1 100644
--- a/include/linux/spinlock.h
+++ b/include/linux/spinlock.h
@@ -244,17 +244,17 @@ do { \
#define spin_lock_irqsave(lock, flags) \
do { \
typecheck(unsigned long, flags); \
- _spin_lock_irqsave(lock, flags); \
+ _spin_lock_irqsave(lock, &flags); \
} while (0)
#define read_lock_irqsave(lock, flags) \
do { \
typecheck(unsigned long, flags); \
- _read_lock_irqsave(lock, flags); \
+ _read_lock_irqsave(lock, &flags); \
} while (0)
#define write_lock_irqsave(lock, flags) \
do { \
typecheck(unsigned long, flags); \
- _write_lock_irqsave(lock, flags); \
+ _write_lock_irqsave(lock, &flags); \
} while (0)
#define spin_lock_irqsave_nested(lock, flags, subclass) \
spin_lock_irqsave(lock, flags)
diff --git a/include/linux/spinlock_api_up.h b/include/linux/spinlock_api_up.h
index 04e1d31..ed9197d 100644
--- a/include/linux/spinlock_api_up.h
+++ b/include/linux/spinlock_api_up.h
@@ -48,34 +48,94 @@
#define __UNLOCK_IRQRESTORE(lock, flags) \
do { local_irq_restore(flags); __UNLOCK(lock); } while (0)

-#define _spin_lock(lock) __LOCK(lock)
-#define _spin_lock_nested(lock, subclass) __LOCK(lock)
-#define _read_lock(lock) __LOCK(lock)
-#define _write_lock(lock) __LOCK(lock)
-#define _spin_lock_bh(lock) __LOCK_BH(lock)
-#define _read_lock_bh(lock) __LOCK_BH(lock)
-#define _write_lock_bh(lock) __LOCK_BH(lock)
-#define _spin_lock_irq(lock) __LOCK_IRQ(lock)
-#define _read_lock_irq(lock) __LOCK_IRQ(lock)
-#define _write_lock_irq(lock) __LOCK_IRQ(lock)
-#define _spin_lock_irqsave(lock, flags) __LOCK_IRQSAVE(lock, flags)
-#define _read_lock_irqsave(lock, flags) __LOCK_IRQSAVE(lock, flags)
-#define _write_lock_irqsave(lock, flags) __LOCK_IRQSAVE(lock, flags)
-#define _spin_trylock(lock) ({ __LOCK(lock); 1; })
-#define _read_trylock(lock) ({ __LOCK(lock); 1; })
-#define _write_trylock(lock) ({ __LOCK(lock); 1; })
-#define _spin_trylock_bh(lock) ({ __LOCK_BH(lock); 1; })
-#define _spin_unlock(lock) __UNLOCK(lock)
-#define _read_unlock(lock) __UNLOCK(lock)
-#define _write_unlock(lock) __UNLOCK(lock)
-#define _spin_unlock_bh(lock) __UNLOCK_BH(lock)
-#define _write_unlock_bh(lock) __UNLOCK_BH(lock)
-#define _read_unlock_bh(lock) __UNLOCK_BH(lock)
-#define _spin_unlock_irq(lock) __UNLOCK_IRQ(lock)
-#define _read_unlock_irq(lock) __UNLOCK_IRQ(lock)
-#define _write_unlock_irq(lock) __UNLOCK_IRQ(lock)
-#define _spin_unlock_irqrestore(lock, flags) __UNLOCK_IRQRESTORE(lock, flags)
-#define _read_unlock_irqrestore(lock, flags) __UNLOCK_IRQRESTORE(lock, flags)
-#define _write_unlock_irqrestore(lock, flags) __UNLOCK_IRQRESTORE(lock, flags)
+static inline void _spin_lock(spinlock_t *lock)
+{ __LOCK(lock); }
+
+static inline void _spin_lock_nested(spinlock_t *lock, int subclass)
+{ __LOCK(lock); }
+
+static inline void _read_lock(rwlock_t *lock)
+{ __LOCK(lock); }
+
+static inline void _write_lock(rwlock_t *lock)
+{ __LOCK(lock); }
+
+static inline void _spin_lock_bh(spinlock_t *lock)
+{ __LOCK_BH(lock); }
+
+static inline void _read_lock_bh(rwlock_t *lock)
+{ __LOCK_BH(lock); }
+
+static inline void _write_lock_bh(rwlock_t *lock)
+{ __LOCK_BH(lock); }
+
+static inline void _spin_lock_irq(spinlock_t *lock)
+{ __LOCK_IRQ(lock); }
+
+static inline void _read_lock_irq(rwlock_t *lock)
+{ __LOCK_IRQ(lock); }
+
+static inline void _write_lock_irq(rwlock_t *lock)
+{ __LOCK_IRQ(lock); }
+
+static inline void _spin_lock_irqsave(spinlock_t *lock, unsigned long *flags)
+{ __LOCK_IRQSAVE(lock, *flags); }
+
+static inline void _read_lock_irqsave(rwlock_t *lock, unsigned long *flags)
+{ __LOCK_IRQSAVE(lock, *flags); }
+
+static inline void _write_lock_irqsave(rwlock_t *lock, unsigned long *flags)
+{ __LOCK_IRQSAVE(lock, *flags); }
+
+static inline int _spin_trylock(spinlock_t *lock)
+{ __LOCK(lock); return 1; }
+
+static inline int _read_trylock(rwlock_t *lock)
+{ __LOCK(lock); return 1; }
+
+static inline int _write_trylock(rwlock_t *lock)
+{ __LOCK(lock); return 1; }
+
+static inline int _spin_trylock_bh(spinlock_t *lock)
+{ __LOCK(lock); return 1; }
+
+static inline void _spin_unlock(spinlock_t *lock)
+{ __UNLOCK(lock); }
+
+static inline void _read_unlock(rwlock_t *lock)
+{ __UNLOCK(lock); }
+
+static inline void _write_unlock(rwlock_t *lock)
+{ __UNLOCK(lock); }
+
+static inline void _spin_unlock_bh(spinlock_t *lock)
+{ __UNLOCK_BH(lock); }
+
+static inline void _read_unlock_bh(rwlock_t *lock)
+{ __UNLOCK_BH(lock); }
+
+static inline void _write_unlock_bh(rwlock_t *lock)
+{ __UNLOCK_BH(lock); }
+
+static inline void _spin_unlock_irq(spinlock_t *lock)
+{ __UNLOCK_IRQ(lock); }
+
+static inline void _read_unlock_irq(rwlock_t *lock)
+{ __UNLOCK_IRQ(lock); }
+
+static inline void _write_unlock_irq(rwlock_t *lock)
+{ __UNLOCK_IRQ(lock); }
+
+static inline void _spin_unlock_irqrestore(spinlock_t *lock,
+ unsigned long flags)
+{ __UNLOCK_IRQRESTORE(lock, flags); }
+
+static inline void _read_unlock_irqrestore(rwlock_t *lock,
+ unsigned long flags)
+{ __UNLOCK_IRQRESTORE(lock, flags); }
+
+static inline void _write_unlock_irqrestore(rwlock_t *lock,
+ unsigned long flags)
+{ __UNLOCK_IRQRESTORE(lock, flags); }

#endif /* __LINUX_SPINLOCK_API_UP_H */
--
1.6.3.3


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