x86/ticketlock: Fix spin_unlock_wait() livelock

[firefly-linux-kernel-4.4.55.git] / arch / x86 / include / asm / spinlock.h

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index bf156ded74b56006a76cc02b8917984117af8afd..abc34e95398d561bad992f626db3642ca4b54c3d 100644 (file)
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -184,8 +184,20 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
 
 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 {
-       while (arch_spin_is_locked(lock))
+       __ticket_t head = ACCESS_ONCE(lock->tickets.head);
+
+       for (;;) {
+               struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
+               /*
+                * We need to check "unlocked" in a loop, tmp.head == head
+                * can be false positive because of overflow.
+                */
+               if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) ||
+                   tmp.head != head)
+                       break;
+
                cpu_relax();
+       }
 }
 
 /*