[PATCH] reduce code in generic spinlock.h

[Dave Hansen]

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The last time lockmeter was ported to 2.5, it was getting a little
messy.  There were separate declarations for spin_*lock() for each
combination of lockmeter and preemption, which made four, plus the
no-smp definition.  While lockmeter's mess isn't the kernel's fault, 
we noticed some some simplifications which could be made to the 
generic spinlock code.  This patch uses a single definition for each 
of the macros, eliminating some redundant code.

In the preemption-off case, spin lock is changed from this:
_raw_spin_lock(lock)
to this:
do {
	preempt_disable();
	_raw_spin_lock(lock)
} while (0)
The preemption-on case is unchanged.

Since preempt_disable() is a do{}while(0) with preemption off anyway,
it gets back to the same effective result as before, with a little
extra work from the compiler.  The preempt_disable() macro just had to
be moved up in the file a bit.

Thanks to Adam Litke <[e-mail]>, who has been doing the
lockmeter port and who initially wrote this patch.

Compiles in all combinations of SMP and preempt.
-- 
Dave Hansen
[e-mail]

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diff -ur linux-2.5.27-clean/include/linux/spinlock.h linux-2.5.27/include/linux/spinlock.h
--- linux-2.5.27-clean/include/linux/spinlock.h	Tue Jul 23 09:19:51 2002
+++ linux-2.5.27/include/linux/spinlock.h	Tue Jul 23 09:26:16 2002
@@ -150,6 +150,14 @@
 		preempt_schedule(); \
 } while (0)
 
+#else /* !CONFIG_PREEMPT */
+#define preempt_get_count()		(0)
+#define preempt_disable()		do { } while(0)
+#define preempt_enable_no_resched()	do { } while(0)
+#define preempt_enable()		do { } while(0)
+#define preempt_check_resched()		do { } while(0)
+#endif /* !CONFIG_PREEMPT */
+
 #define spin_lock(lock)	\
 do { \
 	preempt_disable(); \
@@ -176,26 +184,6 @@
 #define write_unlock(lock)	({_raw_write_unlock(lock); preempt_enable();})
 #define write_trylock(lock)	({preempt_disable();_raw_write_trylock(lock) ? \
 				1 : ({preempt_enable(); 0;});})
-
-#else
-
-#define preempt_get_count()		(0)
-#define preempt_disable()		do { } while (0)
-#define preempt_enable_no_resched()	do {} while(0)
-#define preempt_enable()		do { } while (0)
-#define preempt_check_resched()		do { } while (0)
-
-#define spin_lock(lock)			_raw_spin_lock(lock)
-#define spin_trylock(lock)		_raw_spin_trylock(lock)
-#define spin_unlock(lock)		_raw_spin_unlock(lock)
-#define spin_unlock_no_resched(lock)	_raw_spin_unlock(lock)
-
-#define read_lock(lock)			_raw_read_lock(lock)
-#define read_unlock(lock)		_raw_read_unlock(lock)
-#define write_lock(lock)		_raw_write_lock(lock)
-#define write_unlock(lock)		_raw_write_unlock(lock)
-#define write_trylock(lock)		_raw_write_trylock(lock)
-#endif
 
 /* "lock on reference count zero" */
 #ifndef ATOMIC_DEC_AND_LOCK
Only in linux-2.5.27-clean/include/linux: spinlock.h.orig

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