[PARISC] Fix our spinlock implementation

We actually have two separate bad bugs

1. The read_lock implementation spins with disabled interrupts.  This is
completely wrong
2. Our spin_lock_irqsave should check to see if interrupts were enabled
before the call and re-enable interrupts around the inner spin loop.

The problem is that if we spin with interrupts off, we can't receive
IPIs. This has resulted in a bug where SMP machines suddenly spit
smp_call_function timeout messages and hang.

The scenario I've caught is

CPU0 does a flush_tlb_all holding the vmlist_lock for write.
CPU1 tries a cat of /proc/meminfo which tries to acquire vmlist_lock for
     read
CPU1 is now spinning with interrupts disabled
CPU0 tries to execute a smp_call_function to flush the local tlb caches

This is now a deadlock because CPU1 is spinning with interrupts disabled
and can never receive the IPI

Signed-off-by: James Bottomley <jejb@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

include/asm-parisc/spinlock.h

@@ -11,18 +11,25 @@ static inline int __raw_spin_is_locked(raw_spinlock_t *x)
 	return *a == 0;
 }
 
-#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
 #define __raw_spin_unlock_wait(x) \
 		do { cpu_relax(); } while (__raw_spin_is_locked(x))
 
-static inline void __raw_spin_lock(raw_spinlock_t *x)
+static inline void __raw_spin_lock_flags(raw_spinlock_t *x,
+					 unsigned long flags)
 {
 	volatile unsigned int *a;
 
 	mb();
 	a = __ldcw_align(x);
 	while (__ldcw(a) == 0)
-		while (*a == 0);
+		while (*a == 0)
+			if (flags & PSW_SM_I) {
+				local_irq_enable();
+				cpu_relax();
+				local_irq_disable();
+			} else
+				cpu_relax();
 	mb();
 }
 
@@ -60,26 +67,20 @@ static inline int __raw_spin_trylock(raw_spinlock_t *x)
 
 static  __inline__ void __raw_read_lock(raw_rwlock_t *rw)
 {
-	unsigned long flags;
-	local_irq_save(flags);
 	__raw_spin_lock(&rw->lock);
 
 	rw->counter++;
 
 	__raw_spin_unlock(&rw->lock);
-	local_irq_restore(flags);
 }
 
 static  __inline__ void __raw_read_unlock(raw_rwlock_t *rw)
 {
-	unsigned long flags;
-	local_irq_save(flags);
 	__raw_spin_lock(&rw->lock);
 
 	rw->counter--;
 
 	__raw_spin_unlock(&rw->lock);
-	local_irq_restore(flags);
 }
 
 /* write_lock is less trivial.  We optimistically grab the lock and check