[S390] do local_irq_restore while spinning in spin_lock_irqsave.

In s390's spin_lock_irqsave, interrupts remain disabled while
spinning. In other architectures like x86 and powerpc, interrupts are
re-enabled while spinning if IRQ is not masked before spin_lock_irqsave
is called.

The following patch re-enables interrupts through local_irq_restore
while spinning for a lock acquisition.
This can improve system response.

[[e-mail]: removed saving of pc]

Signed-off-by: Hisashi Hifumi <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/lib/spinlock.c

···
 }
 EXPORT_SYMBOL(_raw_spin_lock_wait);
 
+void _raw_spin_lock_wait_flags(raw_spinlock_t *lp, unsigned long flags)
+{
+	int count = spin_retry;
+	unsigned int cpu = ~smp_processor_id();
+
+	local_irq_restore(flags);
+	while (1) {
+		if (count-- <= 0) {
+			unsigned int owner = lp->owner_cpu;
+			if (owner != 0)
+				_raw_yield_cpu(~owner);
+			count = spin_retry;
+		}
+		if (__raw_spin_is_locked(lp))
+			continue;
+		local_irq_disable();
+		if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
+			return;
+		local_irq_restore(flags);
+	}
+}
+EXPORT_SYMBOL(_raw_spin_lock_wait_flags);
+
 int _raw_spin_trylock_retry(raw_spinlock_t *lp)
 {
 	unsigned int cpu = ~smp_processor_id();

include/asm-s390/spinlock.h

···
  */
 
 #define __raw_spin_is_locked(x) ((x)->owner_cpu != 0)
-#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
 #define __raw_spin_unlock_wait(lock) \
 	do { while (__raw_spin_is_locked(lock)) \
 		 _raw_spin_relax(lock); } while (0)
 
 extern void _raw_spin_lock_wait(raw_spinlock_t *);
+extern void _raw_spin_lock_wait_flags(raw_spinlock_t *, unsigned long flags);
 extern int _raw_spin_trylock_retry(raw_spinlock_t *);
 extern void _raw_spin_relax(raw_spinlock_t *lock);
 
···
 	if (likely(old == 0))
 		return;
 	_raw_spin_lock_wait(lp);
+}
+
+static inline void __raw_spin_lock_flags(raw_spinlock_t *lp,
+					 unsigned long flags)
+{
+	int old;
+
+	old = _raw_compare_and_swap(&lp->owner_cpu, 0, ~smp_processor_id());
+	if (likely(old == 0))
+		return;
+	_raw_spin_lock_wait_flags(lp, flags);
 }
 
 static inline int __raw_spin_trylock(raw_spinlock_t *lp)