s390/spinlock: fix system hang with spin_retry <= 0

On LPAR, when spin_retry is set to <= 0, arch_spin_lock_wait() and
arch_spin_lock_wait_flags() may end up in a while(1) loop w/o doing
any compare and swap operation. To fix this, use do/while instead of
for loop.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index 3ca9de4d9cb9..3f0e682b7e62 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -26,19 +26,20 @@ __setup("spin_retry=", spin_retry_setup);
 
 void arch_spin_lock_wait(arch_spinlock_t *lp)
 {
-        int count = spin_retry;
         unsigned int cpu = SPINLOCK_LOCKVAL;
         unsigned int owner;
+        int count;
 
         while (1) {
                 owner = lp->lock;
                 if (!owner || smp_vcpu_scheduled(~owner)) {
-                        for (count = spin_retry; count > 0; count--) {
+                        count = spin_retry;
+                        do {
                                 if (arch_spin_is_locked(lp))
                                         continue;
                                 if (_raw_compare_and_swap(&lp->lock, 0, cpu))
                                         return;
-                        }
+                        } while (count-- > 0);
                         if (MACHINE_IS_LPAR)
                                 continue;
                 }
@@ -53,22 +54,23 @@ EXPORT_SYMBOL(arch_spin_lock_wait);
 
 void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
 {
-        int count = spin_retry;
         unsigned int cpu = SPINLOCK_LOCKVAL;
         unsigned int owner;
+        int count;
 
         local_irq_restore(flags);
         while (1) {
                 owner = lp->lock;
                 if (!owner || smp_vcpu_scheduled(~owner)) {
-                        for (count = spin_retry; count > 0; count--) {
+                        count = spin_retry;
+                        do {
                                 if (arch_spin_is_locked(lp))
                                         continue;
                                 local_irq_disable();
                                 if (_raw_compare_and_swap(&lp->lock, 0, cpu))
                                         return;
                                 local_irq_restore(flags);
-                        }
+                        } while (count-- > 0);
                         if (MACHINE_IS_LPAR)
                                 continue;
                 }