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authorDipankar Sarma <dipankar@in.ibm.com>2005-12-12 00:37:05 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2005-12-12 08:57:42 -0800
commitab4720ec76b756e1f8705e207a7b392b0453afd6 (patch)
tree1c4235ec8ac0e8e7f75a6f97ea6169e93647004f /kernel/rcupdate.c
parent85b872424984e79519be904e7df02a91ba0a9486 (diff)
[PATCH] add rcu_barrier() synchronization point
This introduces a new interface - rcu_barrier() which waits until all the RCUs queued until this call have been completed. Reiser4 needs this, 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(). Cc: Hans Reiser <reiser@namesys.com> Cc: Vladimir V. Saveliev <vs@namesys.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/rcupdate.c')
-rw-r--r--kernel/rcupdate.c41
1 files changed, 41 insertions, 0 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index c4d159a21e04..f45b91723dc6 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -116,6 +116,10 @@ void fastcall call_rcu(struct rcu_head *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.
@@ -162,6 +166,42 @@ long rcu_batches_completed(void)
return rcu_ctrlblk.completed;
}
+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_GPL(rcu_barrier);
+
/*
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
@@ -457,6 +497,7 @@ static struct notifier_block __devinitdata rcu_nb = {
*/
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 */

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