[PATCH] Deprecate synchronize_kernel, GPL replacement

The synchronize_kernel() primitive is used for quite a few different purposes:
waiting for RCU readers, waiting for NMIs, waiting for interrupts, and so on.
This makes RCU code harder to read, since synchronize_kernel() might or might
not have matching rcu_read_lock()s.  This patch creates a new
synchronize_rcu() that is to be used for RCU readers and a new
synchronize_sched() that is used for the rest.  These two new primitives
currently have the same implementation, but this is might well change with
additional real-time support.  Both new primitives are GPL-only, the old
primitive is deprecated.

Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 20 insertions, 3 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 4d747433916b..fd276adf0fd5 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -157,9 +157,9 @@ static inline int rcu_pending(int cpu)
 /**
  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  *
- * When synchronize_kernel() is invoked on one CPU while other CPUs
+ * When synchronize_rcu() is invoked on one CPU while other CPUs
  * are within RCU read-side critical sections, then the
- * synchronize_kernel() is guaranteed to block until after all the other
+ * synchronize_rcu() is guaranteed to block until after all the other
  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  * on one CPU while other CPUs are within RCU read-side critical
  * sections, invocation of the corresponding RCU callback is deferred
@@ -256,6 +256,21 @@ static inline int rcu_pending(int cpu)
 						(p) = (v); \
 					})
 
+/**
+ * synchronize_sched - block until all CPUs have exited any non-preemptive
+ * kernel code sequences.
+ *
+ * This means that all preempt_disable code sequences, including NMI and
+ * hardware-interrupt handlers, in progress on entry will have completed
+ * before this primitive returns.  However, this does not guarantee that
+ * softirq handlers will have completed, since in some kernels
+ *
+ * This primitive provides the guarantees made by the (deprecated)
+ * synchronize_kernel() API.  In contrast, synchronize_rcu() only
+ * guarantees that rcu_read_lock() sections will have completed.
+ */
+#define synchronize_sched() synchronize_rcu()
+
 extern void rcu_init(void);
 extern void rcu_check_callbacks(int cpu, int user);
 extern void rcu_restart_cpu(int cpu);
@@ -265,7 +280,9 @@ extern void FASTCALL(call_rcu(struct rcu_head *head,
 				void (*func)(struct rcu_head *head)));
 extern void FASTCALL(call_rcu_bh(struct rcu_head *head,
 				void (*func)(struct rcu_head *head)));
-extern void synchronize_kernel(void);
+extern __deprecated_for_modules void synchronize_kernel(void);
+extern void synchronize_rcu(void);
+void synchronize_idle(void);
 
 #endif /* __KERNEL__ */
 #endif /* __LINUX_RCUPDATE_H */