ARM: 7749/1: spinlock: retry trylock operation if strex fails on free lock

[mirror_ubuntu-bionic-kernel.git] / arch / arm / include / asm / spinlock.h

diff --git a/arch/arm/include/asm/spinlock.h b/arch/arm/include/asm/spinlock.h
index 6220e9fdf4c7d0917fe50dc54b23f70502ea43a5..f8b8965666e9b14842786742f48ccdef49000802 100644 (file)
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -97,19 +97,22 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
 
 static inline int arch_spin_trylock(arch_spinlock_t *lock)
 {
-       unsigned long tmp;
+       unsigned long contended, res;
        u32 slock;
 
-       __asm__ __volatile__(
-"      ldrex   %0, [%2]\n"
-"      subs    %1, %0, %0, ror #16\n"
-"      addeq   %0, %0, %3\n"
-"      strexeq %1, %0, [%2]"
-       : "=&r" (slock), "=&r" (tmp)
-       : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
-       : "cc");
-
-       if (tmp == 0) {
+       do {
+               __asm__ __volatile__(
+               "       ldrex   %0, [%3]\n"
+               "       mov     %2, #0\n"
+               "       subs    %1, %0, %0, ror #16\n"
+               "       addeq   %0, %0, %4\n"
+               "       strexeq %2, %0, [%3]"
+               : "=&r" (slock), "=&r" (contended), "=r" (res)
+               : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
+               : "cc");
+       } while (res);
+
+       if (!contended) {
                smp_mb();
                return 1;
        } else {