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

Pull locking fixes from Ingo Molnar:
 "Spinlock performance regression fix, plus documentation fixes"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/static_keys: Fix up the static keys documentation
  locking/qspinlock/x86: Only emit the test-and-set fallback when building guest support
  locking/qspinlock/x86: Fix performance regression under unaccelerated VMs
  locking/static_keys: Fix a silly typo

Documentation/static-keys.txt

@@ -15,8 +15,8 @@ The updated API replacements are:
 
 DEFINE_STATIC_KEY_TRUE(key);
 DEFINE_STATIC_KEY_FALSE(key);
-static_key_likely()
-statick_key_unlikely()
+static_branch_likely()
+static_branch_unlikely()
 
 0) Abstract
 

arch/x86/include/asm/qspinlock.h

@@ -39,18 +39,27 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
 }
 #endif
 
-#define virt_queued_spin_lock virt_queued_spin_lock
-
-static inline bool virt_queued_spin_lock(struct qspinlock *lock)
+#ifdef CONFIG_PARAVIRT
+#define virt_spin_lock virt_spin_lock
+static inline bool virt_spin_lock(struct qspinlock *lock)
 {
 	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
 		return false;
 
-	while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)
-		cpu_relax();
+	/*
+	 * On hypervisors without PARAVIRT_SPINLOCKS support we fall
+	 * back to a Test-and-Set spinlock, because fair locks have
+	 * horrible lock 'holder' preemption issues.
+	 */
+
+	do {
+		while (atomic_read(&lock->val) != 0)
+			cpu_relax();
+	} while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
 
 	return true;
 }
+#endif /* CONFIG_PARAVIRT */
 
 #include <asm-generic/qspinlock.h>
 

include/asm-generic/qspinlock.h

@@ -111,8 +111,8 @@ static inline void queued_spin_unlock_wait(struct qspinlock *lock)
 		cpu_relax();
 }
 
-#ifndef virt_queued_spin_lock
-static __always_inline bool virt_queued_spin_lock(struct qspinlock *lock)
+#ifndef virt_spin_lock
+static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 {
 	return false;
 }

include/linux/jump_label.h

@@ -21,8 +21,8 @@
  *
  * DEFINE_STATIC_KEY_TRUE(key);
  * DEFINE_STATIC_KEY_FALSE(key);
- * static_key_likely()
- * statick_key_unlikely()
+ * static_branch_likely()
+ * static_branch_unlikely()
  *
  * Jump labels provide an interface to generate dynamic branches using
  * self-modifying code. Assuming toolchain and architecture support, if we
@@ -45,12 +45,10 @@
  * statement, setting the key to true requires us to patch in a jump
  * to the out-of-line of true branch.
  *
- * In addtion to static_branch_{enable,disable}, we can also reference count
+ * In addition to static_branch_{enable,disable}, we can also reference count
  * the key or branch direction via static_branch_{inc,dec}. Thus,
  * static_branch_inc() can be thought of as a 'make more true' and
- * static_branch_dec() as a 'make more false'. The inc()/dec()
- * interface is meant to be used exclusively from the inc()/dec() for a given
- * key.
+ * static_branch_dec() as a 'make more false'.
  *
  * Since this relies on modifying code, the branch modifying functions
  * must be considered absolute slow paths (machine wide synchronization etc.).

kernel/locking/qspinlock.c

@@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	if (pv_enabled())
 		goto queue;
 
-	if (virt_queued_spin_lock(lock))
+	if (virt_spin_lock(lock))
 		return;
 
 	/*