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

Pull RCU changes from Ingo Molnar:

 0. 'idle RCU':

     Adds RCU APIs that allow non-idle tasks to enter RCU idle mode and
     provides x86 code to make use of them, allowing RCU to treat
     user-mode execution as an extended quiescent state when the new
     RCU_USER_QS kernel configuration parameter is specified.  (Work is
     in progress to port this to a few other architectures, but is not
     part of this series.)

 1.  A fix for a latent bug that has been in RCU ever since the addition
     of CPU stall warnings.  This bug results in false-positive stall
     warnings, but thus far only on embedded systems with severely
     cut-down userspace configurations.

 2.  Further reductions in latency spikes for huge systems, along with
     additional boot-time adaptation to the actual hardware.

     This is a large change, as it moves RCU grace-period initialization
     and cleanup, along with quiescent-state forcing, from softirq to a
     kthread.  However, it appears to be in quite good shape (famous
     last words).

 3.  Updates to documentation and rcutorture, the latter category
     including keeping statistics on CPU-hotplug latencies and fixing
     some initialization-time races.

 4.  CPU-hotplug fixes and improvements.

 5.  Idle-loop fixes that were omitted on an earlier submission.

 6.  Miscellaneous fixes and improvements

In certain RCU configurations new kernel threads will show up (rcu_bh,
rcu_sched), showing RCU processing overhead.

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (90 commits)
  rcu: Apply micro-optimization and int/bool fixes to RCU's idle handling
  rcu: Userspace RCU extended QS selftest
  x86: Exit RCU extended QS on notify resume
  x86: Use the new schedule_user API on userspace preemption
  rcu: Exit RCU extended QS on user preemption
  rcu: Exit RCU extended QS on kernel preemption after irq/exception
  x86: Exception hooks for userspace RCU extended QS
  x86: Unspaghettize do_general_protection()
  x86: Syscall hooks for userspace RCU extended QS
  rcu: Switch task's syscall hooks on context switch
  rcu: Ignore userspace extended quiescent state by default
  rcu: Allow rcu_user_enter()/exit() to nest
  rcu: Settle config for userspace extended quiescent state
  rcu: Make RCU_FAST_NO_HZ handle adaptive ticks
  rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIs
  rcu: New rcu_user_enter() and rcu_user_exit() APIs
  ia64: Add missing RCU idle APIs on idle loop
  xtensa: Add missing RCU idle APIs on idle loop
  score: Add missing RCU idle APIs on idle loop
  parisc: Add missing RCU idle APIs on idle loop
  ...

1 files changed, 18 insertions, 15 deletions

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 547b1fe5b052..e4c6a598d6f7 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -56,25 +56,28 @@ static void __call_rcu(struct rcu_head *head,
 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 
 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
-static void rcu_idle_enter_common(long long oldval)
+static void rcu_idle_enter_common(long long newval)
 {
-        if (rcu_dynticks_nesting) {
+        if (newval) {
                 RCU_TRACE(trace_rcu_dyntick("--=",
-                                            oldval, rcu_dynticks_nesting));
+                                            rcu_dynticks_nesting, newval));
+                rcu_dynticks_nesting = newval;
                 return;
         }
-        RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
+        RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
         if (!is_idle_task(current)) {
                 struct task_struct *idle = idle_task(smp_processor_id());
 
                 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
-                                            oldval, rcu_dynticks_nesting));
+                                            rcu_dynticks_nesting, newval));
                 ftrace_dump(DUMP_ALL);
                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
                           current->pid, current->comm,
                           idle->pid, idle->comm); /* must be idle task! */
         }
         rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
+        barrier();
+        rcu_dynticks_nesting = newval;
 }
 
 /*
@@ -84,17 +87,16 @@ static void rcu_idle_enter_common(long long oldval)
 void rcu_idle_enter(void)
 {
         unsigned long flags;
-        long long oldval;
+        long long newval;
 
         local_irq_save(flags);
-        oldval = rcu_dynticks_nesting;
         WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
         if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
             DYNTICK_TASK_NEST_VALUE)
-                rcu_dynticks_nesting = 0;
+                newval = 0;
         else
-                rcu_dynticks_nesting  -= DYNTICK_TASK_NEST_VALUE;
-        rcu_idle_enter_common(oldval);
+                newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
+        rcu_idle_enter_common(newval);
         local_irq_restore(flags);
 }
 EXPORT_SYMBOL_GPL(rcu_idle_enter);
@@ -105,15 +107,15 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter);
 void rcu_irq_exit(void)
 {
         unsigned long flags;
-        long long oldval;
+        long long newval;
 
         local_irq_save(flags);
-        oldval = rcu_dynticks_nesting;
-        rcu_dynticks_nesting--;
-        WARN_ON_ONCE(rcu_dynticks_nesting < 0);
-        rcu_idle_enter_common(oldval);
+        newval = rcu_dynticks_nesting - 1;
+        WARN_ON_ONCE(newval < 0);
+        rcu_idle_enter_common(newval);
         local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_exit);
 
 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 static void rcu_idle_exit_common(long long oldval)
@@ -171,6 +173,7 @@ void rcu_irq_enter(void)
         rcu_idle_exit_common(oldval);
         local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(rcu_irq_enter);
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC