Merge commit '29ce831000081dd757d3116bf774aafffc4b6b20' into next

* commit '29ce831000081dd757d3116bf774aafffc4b6b20': (34 commits)
  rcu: provide rcu_virt_note_context_switch() function.
  rcu: get rid of signed overflow in check_cpu_stall()
  rcu: optimize rcutiny
  rcu: prevent call_rcu() from diving into rcu core if irqs disabled
  rcu: further lower priority in rcu_yield()
  rcu: introduce kfree_rcu()
  rcu: fix spelling
  rcu: call __rcu_read_unlock() in exit_rcu for tree RCU
  rcu: Converge TINY_RCU expedited and normal boosting
  rcu: remove useless ->boosted_this_gp field
  rcu: code cleanups in TINY_RCU priority boosting.
  rcu: Switch to this_cpu() primitives
  rcu: Use WARN_ON_ONCE for DEBUG_OBJECTS_RCU_HEAD warnings
  rcu: mark rcutorture boosting callback as being on-stack
  rcu: add DEBUG_OBJECTS_RCU_HEAD check for alignment
  rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPT
  rcu: Add forward-progress diagnostic for per-CPU kthreads
  rcu: add grace-period age and more kthread state to tracing
  rcu: fix tracing bug thinko on boost-balk attribution
  rcu: update tracing documentation for new rcutorture and rcuboost
  ...

Pulling in rcu_virt_note_context_switch().

Signed-off-by: Avi Kivity <avi@redhat.com>

* commit '29ce831000081dd757d3116bf774aafffc4b6b20': (34 commits)
  rcu: provide rcu_virt_note_context_switch() function.
  rcu: get rid of signed overflow in check_cpu_stall()
  rcu: optimize rcutiny
  rcu: prevent call_rcu() from diving into rcu core if irqs disabled
  rcu: further lower priority in rcu_yield()
  rcu: introduce kfree_rcu()
  rcu: fix spelling
  rcu: call __rcu_read_unlock() in exit_rcu for tree RCU
  rcu: Converge TINY_RCU expedited and normal boosting
  rcu: remove useless ->boosted_this_gp field
  rcu: code cleanups in TINY_RCU priority boosting.
  rcu: Switch to this_cpu() primitives
  rcu: Use WARN_ON_ONCE for DEBUG_OBJECTS_RCU_HEAD warnings
  rcu: mark rcutorture boosting callback as being on-stack
  rcu: add DEBUG_OBJECTS_RCU_HEAD check for alignment
  rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPT
  rcu: Add forward-progress diagnostic for per-CPU kthreads
  rcu: add grace-period age and more kthread state to tracing
  rcu: fix tracing bug thinko on boost-balk attribution
  rcu: update tracing documentation for new rcutorture and rcuboost
  ...

9 files changed, 1438 insertions, 445 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f3240e987928..7784bd216b6a 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -142,10 +142,17 @@ static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
                  * Ensure that queued callbacks are all executed.
                  * If we detect that we are nested in a RCU read-side critical
                  * section, we should simply fail, otherwise we would deadlock.
+                 * In !PREEMPT configurations, there is no way to tell if we are
+                 * in a RCU read-side critical section or not, so we never
+                 * attempt any fixup and just print a warning.
                  */
+#ifndef CONFIG_PREEMPT
+                WARN_ON_ONCE(1);
+                return 0;
+#endif
                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                     irqs_disabled()) {
-                        WARN_ON(1);
+                        WARN_ON_ONCE(1);
                         return 0;
                 }
                 rcu_barrier();
@@ -184,10 +191,17 @@ static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
                  * Ensure that queued callbacks are all executed.
                  * If we detect that we are nested in a RCU read-side critical
                  * section, we should simply fail, otherwise we would deadlock.
+                 * In !PREEMPT configurations, there is no way to tell if we are
+                 * in a RCU read-side critical section or not, so we never
+                 * attempt any fixup and just print a warning.
                  */
+#ifndef CONFIG_PREEMPT
+                WARN_ON_ONCE(1);
+                return 0;
+#endif
                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                     irqs_disabled()) {
-                        WARN_ON(1);
+                        WARN_ON_ONCE(1);
                         return 0;
                 }
                 rcu_barrier();
@@ -214,15 +228,17 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
                  * Ensure that queued callbacks are all executed.
                  * If we detect that we are nested in a RCU read-side critical
                  * section, we should simply fail, otherwise we would deadlock.
-                 * Note that the machinery to reliably determine whether
-                 * or not we are in an RCU read-side critical section
-                 * exists only in the preemptible RCU implementations
-                 * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why
-                 * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT.
+                 * In !PREEMPT configurations, there is no way to tell if we are
+                 * in a RCU read-side critical section or not, so we never
+                 * attempt any fixup and just print a warning.
                  */
+#ifndef CONFIG_PREEMPT
+                WARN_ON_ONCE(1);
+                return 0;
+#endif
                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                     irqs_disabled()) {
-                        WARN_ON(1);
+                        WARN_ON_ONCE(1);
                         return 0;
                 }
                 rcu_barrier();
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 0c343b9a46d5..421abfd3641d 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -40,10 +40,10 @@
 static struct task_struct *rcu_kthread_task;
 static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
 static unsigned long have_rcu_kthread_work;
-static void invoke_rcu_kthread(void);
 
 /* Forward declarations for rcutiny_plugin.h. */
 struct rcu_ctrlblk;
+static void invoke_rcu_kthread(void);
 static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
 static int rcu_kthread(void *arg);
 static void __call_rcu(struct rcu_head *head,
@@ -79,36 +79,45 @@ void rcu_exit_nohz(void)
 #endif /* #ifdef CONFIG_NO_HZ */
 
 /*
- * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
- * Also disable irqs to avoid confusion due to interrupt handlers
+ * Helper function for rcu_sched_qs() and rcu_bh_qs().
+ * Also irqs are disabled to avoid confusion due to interrupt handlers
  * invoking call_rcu().
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-        unsigned long flags;
-
-        local_irq_save(flags);
         if (rcp->rcucblist != NULL &&
             rcp->donetail != rcp->curtail) {
                 rcp->donetail = rcp->curtail;
-                local_irq_restore(flags);
                 return 1;
         }
-        local_irq_restore(flags);
 
         return 0;
 }
 
 /*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_kthread(void)
+{
+        have_rcu_kthread_work = 1;
+        wake_up(&rcu_kthread_wq);
+}
+
+/*
  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
  * are at it, given that any rcu quiescent state is also an rcu_bh
  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  */
 void rcu_sched_qs(int cpu)
 {
+        unsigned long flags;
+
+        local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
             rcu_qsctr_help(&rcu_bh_ctrlblk))
                 invoke_rcu_kthread();
+        local_irq_restore(flags);
 }
 
 /*
@@ -116,8 +125,12 @@ void rcu_sched_qs(int cpu)
  */
 void rcu_bh_qs(int cpu)
 {
+        unsigned long flags;
+
+        local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
                 invoke_rcu_kthread();
+        local_irq_restore(flags);
 }
 
 /*
@@ -167,7 +180,7 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)