From: Hans Reiser <reiser@namesys.com>
This patch is by Dipankar Sarma <dipankar@in.ibm.com>. His description:
This patch introduces a new interface - rcu_barrier() which waits until
all the RCUs queued until this call have been completed.
Reiser4 needs this patch, because we do more than just freeing memory object
in our RCU callback: we also remove it from the list hanging off super-block.
This means, that before freeing reiser4-specific portion of super-block
(during umount) we have to wait until all pending RCU callbacks are executed.
The only change of reiser4 made to the original patch, is exporting of
rcu_barrier().
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
include/linux/rcupdate.h | 2 ++
kernel/rcupdate.c | 41 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 43 insertions(+)
diff -puN include/linux/rcupdate.h~reiser4-rcu-barrier include/linux/rcupdate.h
--- devel/include/linux/rcupdate.h~reiser4-rcu-barrier 2005-08-06 15:35:09.000000000 -0700
+++ devel-akpm/include/linux/rcupdate.h 2005-08-06 15:35:09.000000000 -0700
@@ -99,6 +99,7 @@ struct rcu_data {
struct rcu_head *donelist;
struct rcu_head **donetail;
int cpu;
+ struct rcu_head barrier;
};
DECLARE_PER_CPU(struct rcu_data, rcu_data);
@@ -283,6 +284,7 @@ extern void FASTCALL(call_rcu_bh(struct
extern __deprecated_for_modules void synchronize_kernel(void);
extern void synchronize_rcu(void);
void synchronize_idle(void);
+extern void rcu_barrier(void);
#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */
diff -puN kernel/rcupdate.c~reiser4-rcu-barrier kernel/rcupdate.c
--- devel/kernel/rcupdate.c~reiser4-rcu-barrier 2005-08-06 15:35:09.000000000 -0700
+++ devel-akpm/kernel/rcupdate.c 2005-08-06 15:35:09.000000000 -0700
@@ -98,6 +98,10 @@ void fastcall call_rcu(struct rcu_head *
local_irq_restore(flags);
}
+static atomic_t rcu_barrier_cpu_count;
+static struct semaphore rcu_barrier_sema;
+static struct completion rcu_barrier_completion;
+
/**
* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
@@ -129,6 +133,42 @@ void fastcall call_rcu_bh(struct rcu_hea
local_irq_restore(flags);
}
+static void rcu_barrier_callback(struct rcu_head *notused)
+{
+ if (atomic_dec_and_test(&rcu_barrier_cpu_count))
+ complete(&rcu_barrier_completion);
+}
+
+/*
+ * Called with preemption disabled, and from cross-cpu IRQ context.
+ */
+static void rcu_barrier_func(void *notused)
+{
+ int cpu = smp_processor_id();
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ struct rcu_head *head;
+
+ head = &rdp->barrier;
+ atomic_inc(&rcu_barrier_cpu_count);
+ call_rcu(head, rcu_barrier_callback);
+}
+
+/**
+ * rcu_barrier - Wait until all the in-flight RCUs are complete.
+ */
+void rcu_barrier(void)
+{
+ BUG_ON(in_interrupt());
+ /* Take cpucontrol semaphore to protect against CPU hotplug */
+ down(&rcu_barrier_sema);
+ init_completion(&rcu_barrier_completion);
+ atomic_set(&rcu_barrier_cpu_count, 0);
+ on_each_cpu(rcu_barrier_func, NULL, 0, 1);
+ wait_for_completion(&rcu_barrier_completion);
+ up(&rcu_barrier_sema);
+}
+EXPORT_SYMBOL(rcu_barrier);
+
/*
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
@@ -423,6 +463,7 @@ static struct notifier_block __devinitda
*/
void __init rcu_init(void)
{
+ sema_init(&rcu_barrier_sema, 1);
rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
(void *)(long)smp_processor_id());
/* Register notifier for non-boot CPUs */
_