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Subject[RFC,PATCH 2/4] 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: <paulmck@us.ibm.com>
---
Depends on earlier "Add deprecated_for_modules" patch.
include/linux/rcupdate.h | 24 +++++++++++++++++++++---
kernel/rcupdate.c | 16 ++++++++++++++--
2 files changed, 35 insertions(+), 5 deletions(-)
diff -urpN -X dontdiff linux-2.6.12-rc1/include/linux/rcupdate.h linux-2.6.12-rc1-bettersk/include/linux/rcupdate.h
--- linux-2.6.12-rc1/include/linux/rcupdate.h Tue Mar 1 23:37:50 2005
+++ linux-2.6.12-rc1-bettersk/include/linux/rcupdate.h Sat Apr 2 13:06:15 2005
@@ -41,6 +41,7 @@
#include <linux/percpu.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
+#include <linux/module.h>

/**
* struct rcu_head - callback structure for use with RCU
@@ -157,9 +158,9 @@ 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 +257,21 @@ 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 +281,9 @@ extern void FASTCALL(call_rcu(struct rcu
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 */
diff -urpN -X dontdiff linux-2.6.12-rc1/kernel/rcupdate.c linux-2.6.12-rc1-bettersk/kernel/rcupdate.c
--- linux-2.6.12-rc1/kernel/rcupdate.c Tue Mar 1 23:37:30 2005
+++ linux-2.6.12-rc1-bettersk/kernel/rcupdate.c Sat Apr 2 13:10:09 2005
@@ -444,15 +444,18 @@ static void wakeme_after_rcu(struct rcu_
}

/**
- * synchronize_kernel - wait until a grace period has elapsed.
+ * synchronize_rcu - wait until a grace period has elapsed.
*
* Control will return to the caller some time after a full grace
* period has elapsed, in other words after all currently executing RCU
* read-side critical sections have completed. RCU read-side critical
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
* and may be nested.
+ *
+ * If your read-side code is not protected by rcu_read_lock(), do -not-
+ * use synchronize_rcu().
*/
-void synchronize_kernel(void)
+void synchronize_rcu(void)
{
struct rcu_synchronize rcu;

@@ -464,7 +467,16 @@ void synchronize_kernel(void)
wait_for_completion(&rcu.completion);
}

+/*
+ * Deprecated, use synchronize_rcu() or synchronize_sched() instead.
+ */
+void synchronize_kernel(void)
+{
+ synchronize_rcu();
+}
+
module_param(maxbatch, int, 0);
EXPORT_SYMBOL(call_rcu);
EXPORT_SYMBOL(call_rcu_bh);
+EXPORT_SYMBOL_GPL(synchronize_rcu);
EXPORT_SYMBOL(synchronize_kernel);
-
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