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

Pull locking updates from Ingo Molnar:

 - improve rwsem scalability

 - add uninitialized rwsem debugging check

 - reduce lockdep's stacktrace memory usage and add diagnostics

 - misc cleanups, code consolidation and constification

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  mutex: Fix up mutex_waiter usage
  locking/mutex: Use mutex flags macro instead of hard code
  locking/mutex: Make __mutex_owner static to mutex.c
  locking/qspinlock,x86: Clarify virt_spin_lock_key
  locking/rwsem: Check for operations on an uninitialized rwsem
  locking/rwsem: Make handoff writer optimistically spin on owner
  locking/lockdep: Report more stack trace statistics
  locking/lockdep: Reduce space occupied by stack traces
  stacktrace: Constify 'entries' arguments
  locking/lockdep: Make it clear that what lock_class::key points at is not modified

arch/x86/include/asm/qspinlock.h

@@ -63,10 +63,25 @@ static inline bool vcpu_is_preempted(long cpu)
 #endif
 
 #ifdef CONFIG_PARAVIRT
+/*
+ * virt_spin_lock_key - enables (by default) the virt_spin_lock() hijack.
+ *
+ * Native (and PV wanting native due to vCPU pinning) should disable this key.
+ * It is done in this backwards fashion to only have a single direction change,
+ * which removes ordering between native_pv_spin_init() and HV setup.
+ */
 DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
 
 void native_pv_lock_init(void) __init;
 
+/*
+ * Shortcut for the queued_spin_lock_slowpath() function that allows
+ * virt to hijack it.
+ *
+ * Returns:
+ *   true - lock has been negotiated, all done;
+ *   false - queued_spin_lock_slowpath() will do its thing.
+ */
 #define virt_spin_lock virt_spin_lock
 static inline bool virt_spin_lock(struct qspinlock *lock)
 {