[PATCH] spinlock debugging on uniprocessors

Patch from Manfred Spraul <manfred@colorfullife.com>

This enables spinlock debuggng on uniprocessor builds, under
CONFIG_DEBUG_SPINLOCK.

The reason I want this is that one day we'll need to pull out the debugging
support from the timer code which detects uninitialised timers.  And once
that has gone, uniprocessor developers and testers have no way of detecting
uninitialised timers - there will be mysterious deadlocks on SMP machines.
And there will surely be more uninitialised timers

The patch also removes the last pieces of the support for including
<asm/spinlock.h> directly.  Doesn't work since (IIRC) 2.3.x

include/linux/spinlock.h

@@ -37,30 +37,120 @@
 #ifdef CONFIG_SMP
 #include <asm/spinlock.h>
 
-/*
- * !CONFIG_SMP and spin_lock_init not previously defined
- * (e.g. by including include/asm/spinlock.h)
- */
-#elif !defined(spin_lock_init)
+#else
 
-#ifndef CONFIG_PREEMPT
+#if !defined(CONFIG_PREEMPT) && !defined(CONFIG_DEBUG_SPINLOCK)
 # define atomic_dec_and_lock(atomic,lock) atomic_dec_and_test(atomic)
 # define ATOMIC_DEC_AND_LOCK
 #endif
 
+#ifdef CONFIG_DEBUG_SPINLOCK
+ 
+#define SPINLOCK_MAGIC	0x1D244B3C
+typedef struct {
+	unsigned long magic;
+	volatile unsigned long lock;
+	volatile unsigned int babble;
+	const char *module;
+	char *owner;
+	int oline;
+} spinlock_t;
+#define SPIN_LOCK_UNLOCKED (spinlock_t) { SPINLOCK_MAGIC, 0, 10, __FILE__ , NULL, 0}
+
+#define spin_lock_init(x) \
+	do { \
+		(x)->magic = SPINLOCK_MAGIC; \
+		(x)->lock = 0; \
+		(x)->babble = 5; \
+		(x)->module = __FILE__; \
+		(x)->owner = NULL; \
+		(x)->oline = 0; \
+	} while (0)
+
+#define CHECK_LOCK(x) \
+	do { \
+	 	if ((x)->magic != SPINLOCK_MAGIC) { \
+			printk(KERN_ERR "%s:%d: spin_is_locked on uninitialized spinlock %p.\n", \
+					__FILE__, __LINE__, (x)); \
+		} \
+	} while(0)
+
+#define _raw_spin_lock(x)		\
+	do { \
+	 	CHECK_LOCK(x); \
+		if ((x)->lock&&(x)->babble) { \
+			printk("%s:%d: spin_lock(%s:%p) already locked by %s/%d\n", \
+					__FILE__,__LINE__, (x)->module, \
+					(x), (x)->owner, (x)->oline); \
+			(x)->babble--; \
+		} \
+		(x)->lock = 1; \
+		(x)->owner = __FILE__; \
+		(x)->oline = __LINE__; \
+	} while (0)
+
+/* without debugging, spin_is_locked on UP always says
+ * FALSE. --> printk if already locked. */
+#define spin_is_locked(x) \
+	({ \
+	 	CHECK_LOCK(x); \
+		if ((x)->lock&&(x)->babble) { \
+			printk("%s:%d: spin_is_locked(%s:%p) already locked by %s/%d\n", \
+					__FILE__,__LINE__, (x)->module, \
+					(x), (x)->owner, (x)->oline); \
+			(x)->babble--; \
+		} \
+		0; \
+	})
+
+/* without debugging, spin_trylock on UP always says
+ * TRUE. --> printk if already locked. */
+#define _raw_spin_trylock(x) \
+	({ \
+	 	CHECK_LOCK(x); \
+		if ((x)->lock&&(x)->babble) { \
+			printk("%s:%d: spin_trylock(%s:%p) already locked by %s/%d\n", \
+					__FILE__,__LINE__, (x)->module, \
+					(x), (x)->owner, (x)->oline); \
+			(x)->babble--; \
+		} \
+		(x)->lock = 1; \
+		(x)->owner = __FILE__; \
+		(x)->oline = __LINE__; \
+		1; \
+	})
+
+#define spin_unlock_wait(x)	\
+	do { \
+	 	CHECK_LOCK(x); \
+		if ((x)->lock&&(x)->babble) { \
+			printk("%s:%d: spin_unlock_wait(%s:%p) owned by %s/%d\n", \
+					__FILE__,__LINE__, (x)->module, (x), \
+					(x)->owner, (x)->oline); \
+			(x)->babble--; \
+		}\
+	} while (0)
+
+#define _raw_spin_unlock(x) \
+	do { \
+	 	CHECK_LOCK(x); \
+		if (!(x)->lock&&(x)->babble) { \
+			printk("%s:%d: spin_unlock(%s:%p) not locked\n", \
+					__FILE__,__LINE__, (x)->module, (x));\
+			(x)->babble--; \
+		} \
+		(x)->lock = 0; \
+	} while (0)
+#else
 /*
  * gcc versions before ~2.95 have a nasty bug with empty initializers.
  */
 #if (__GNUC__ > 2)
   typedef struct { } spinlock_t;
-  typedef struct { } rwlock_t;
   #define SPIN_LOCK_UNLOCKED (spinlock_t) { }
-  #define RW_LOCK_UNLOCKED (rwlock_t) { }
 #else
   typedef struct { int gcc_is_buggy; } spinlock_t;
-  typedef struct { int gcc_is_buggy; } rwlock_t;
   #define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 }
-  #define RW_LOCK_UNLOCKED (rwlock_t) { 0 }
 #endif
 
 /*
@@ -72,6 +162,18 @@
 #define _raw_spin_trylock(lock)	((void)(lock), 1)
 #define spin_unlock_wait(lock)	do { (void)(lock); } while(0)
 #define _raw_spin_unlock(lock)	do { (void)(lock); } while(0)
+#endif /* CONFIG_DEBUG_SPINLOCK */
+
+/* RW spinlocks: No debug version */
+
+#if (__GNUC__ > 2)
+  typedef struct { } rwlock_t;
+  #define RW_LOCK_UNLOCKED (rwlock_t) { }
+#else
+  typedef struct { int gcc_is_buggy; } rwlock_t;
+  #define RW_LOCK_UNLOCKED (rwlock_t) { 0 }
+#endif
+
 #define rwlock_init(lock)	do { (void)(lock); } while(0)
 #define _raw_read_lock(lock)	do { (void)(lock); } while(0)
 #define _raw_read_unlock(lock)	do { (void)(lock); } while(0)