rcu: Permit call_rcu() from CPU_DYING notifiers

[linux-flexiantxendom0-3.2.10.git] / kernel / rcu.h

diff --git a/kernel/rcu.h b/kernel/rcu.h
index 30876f4..8ba99cd 100644 (file)
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -33,8 +33,27 @@
  * Process-level increment to ->dynticks_nesting field.  This allows for
  * architectures that use half-interrupts and half-exceptions from
  * process context.
+ *
+ * DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
+ * that counts the number of process-based reasons why RCU cannot
+ * consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
+ * is the value used to increment or decrement this field.
+ *
+ * The rest of the bits could in principle be used to count interrupts,
+ * but this would mean that a negative-one value in the interrupt
+ * field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
+ * We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
+ * that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
+ * The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
+ * initial exit from idle.
  */
-#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
+#define DYNTICK_TASK_NEST_WIDTH 7
+#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
+#define DYNTICK_TASK_NEST_MASK  (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
+#define DYNTICK_TASK_FLAG         ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
+#define DYNTICK_TASK_MASK         ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
+#define DYNTICK_TASK_EXIT_IDLE    (DYNTICK_TASK_NEST_VALUE + \
+                                   DYNTICK_TASK_FLAG)
 
 /*
  * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally