Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking tree changes from Ingo Molnar:
 "Two changes: a documentation update and a ticket locks live lock fix"

* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/ticketlock: Fix spin_unlock_wait() livelock
  locking/lglocks: Add documentation of current lglocks implementation

1 files changed, 13 insertions, 1 deletions

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 9295016485c9..a4efe477ceab 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -183,8 +183,20 @@ 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();
+        }
 }
 
 /*