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

Pull locking and misc x86 updates from Ingo Molnar:
 "Lots of changes in this cycle - in part because locking/core attracted
  a number of related x86 low level work which was easier to handle in a
  single tree:

   - Linux Kernel Memory Consistency Model updates (Alan Stern, Paul E.
     McKenney, Andrea Parri)

   - lockdep scalability improvements and micro-optimizations (Waiman
     Long)

   - rwsem improvements (Waiman Long)

   - spinlock micro-optimization (Matthew Wilcox)

   - qspinlocks: Provide a liveness guarantee (more fairness) on x86.
     (Peter Zijlstra)

   - Add support for relative references in jump tables on arm64, x86
     and s390 to optimize jump labels (Ard Biesheuvel, Heiko Carstens)

   - Be a lot less permissive on weird (kernel address) uaccess faults
     on x86: BUG() when uaccess helpers fault on kernel addresses (Jann
     Horn)

   - macrofy x86 asm statements to un-confuse the GCC inliner. (Nadav
     Amit)

   - ... and a handful of other smaller changes as well"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (57 commits)
  locking/lockdep: Make global debug_locks* variables read-mostly
  locking/lockdep: Fix debug_locks off performance problem
  locking/pvqspinlock: Extend node size when pvqspinlock is configured
  locking/qspinlock_stat: Count instances of nested lock slowpaths
  locking/qspinlock, x86: Provide liveness guarantee
  x86/asm: 'Simplify' GEN_*_RMWcc() macros
  locking/qspinlock: Rework some comments
  locking/qspinlock: Re-order code
  locking/lockdep: Remove duplicated 'lock_class_ops' percpu array
  x86/defconfig: Enable CONFIG_USB_XHCI_HCD=y
  futex: Replace spin_is_locked() with lockdep
  locking/lockdep: Make class->ops a percpu counter and move it under CONFIG_DEBUG_LOCKDEP=y
  x86/jump-labels: Macrofy inline assembly code to work around GCC inlining bugs
  x86/cpufeature: Macrofy inline assembly code to work around GCC inlining bugs
  x86/extable: Macrofy inline assembly code to work around GCC inlining bugs
  x86/paravirt: Work around GCC inlining bugs when compiling paravirt ops
  x86/bug: Macrofy the BUG table section handling, to work around GCC inlining bugs
  x86/alternatives: Macrofy lock prefixes to work around GCC inlining bugs
  x86/refcount: Work around GCC inlining bug
  x86/objtool: Use asm macros to work around GCC inlining bugs
  ...

1 files changed, 13 insertions, 2 deletions

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 3064c50e181e..09b180063ee1 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -180,7 +180,7 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem,
                  * but it gives the spinners an early indication that the
                  * readers now have the lock.
                  */
-                rwsem_set_reader_owned(sem);
+                __rwsem_set_reader_owned(sem, waiter->task);
         }
 
         /*
@@ -233,8 +233,19 @@ __rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
         waiter.type = RWSEM_WAITING_FOR_READ;
 
         raw_spin_lock_irq(&sem->wait_lock);
-        if (list_empty(&sem->wait_list))
+        if (list_empty(&sem->wait_list)) {
+                /*
+                 * In case the wait queue is empty and the lock isn't owned
+                 * by a writer, this reader can exit the slowpath and return
+                 * immediately as its RWSEM_ACTIVE_READ_BIAS has already
+                 * been set in the count.
+                 */
+                if (atomic_long_read(&sem->count) >= 0) {
+                        raw_spin_unlock_irq(&sem->wait_lock);
+                        return sem;
+                }
                 adjustment += RWSEM_WAITING_BIAS;
+        }
         list_add_tail(&waiter.list, &sem->wait_list);
 
         /* we're now waiting on the lock, but no longer actively locking */