in_atomic(): document why it is unsuitable for general use

[sfrench/cifs-2.6.git] / include / linux / hardirq.h

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 2961ec788046627c823feb291d7d522f15982fbf..897f723bd222f73a9c9e72519fe4b8cd14e40f14 100644 (file)
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -72,6 +72,13 @@
 #define in_softirq()           (softirq_count())
 #define in_interrupt()         (irq_count())
 
+/*
+ * Are we running in atomic context?  WARNING: this macro cannot
+ * always detect atomic context; in particular, it cannot know about
+ * held spinlocks in non-preemptible kernels.  Thus it should not be
+ * used in the general case to determine whether sleeping is possible.
+ * Do not use in_atomic() in driver code.
+ */
 #define in_atomic()            ((preempt_count() & ~PREEMPT_ACTIVE) != 0)
 
 #ifdef CONFIG_PREEMPT
@@ -109,6 +116,14 @@ static inline void account_system_vtime(struct task_struct *tsk)
 }
 #endif
 
+#if defined(CONFIG_PREEMPT_RCU) && defined(CONFIG_NO_HZ)
+extern void rcu_irq_enter(void);
+extern void rcu_irq_exit(void);
+#else
+# define rcu_irq_enter() do { } while (0)
+# define rcu_irq_exit() do { } while (0)
+#endif /* CONFIG_PREEMPT_RCU */
+
 /*
  * It is safe to do non-atomic ops on ->hardirq_context,
  * because NMI handlers may not preempt and the ops are
@@ -117,6 +132,7 @@ static inline void account_system_vtime(struct task_struct *tsk)
  */
 #define __irq_enter()                                  \
        do {                                            \
+               rcu_irq_enter();                        \
                account_system_vtime(current);          \
                add_preempt_count(HARDIRQ_OFFSET);      \
                trace_hardirq_enter();                  \
@@ -135,6 +151,7 @@ extern void irq_enter(void);
                trace_hardirq_exit();                   \
                account_system_vtime(current);          \
                sub_preempt_count(HARDIRQ_OFFSET);      \
+               rcu_irq_exit();                         \
        } while (0)
 
 /*