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-rw-r--r--kernel/smp.c83
1 files changed, 44 insertions, 39 deletions
diff --git a/kernel/smp.c b/kernel/smp.c
index bbedbb7..6ecf4b9 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -74,9 +74,16 @@ static void generic_exec_single(int cpu, struct call_single_data *data)
spin_unlock_irqrestore(&dst->lock, flags);
/*
- * Make the list addition visible before sending the ipi.
+ * The list addition should be visible before sending the IPI
+ * handler locks the list to pull the entry off it because of
+ * normal cache coherency rules implied by spinlocks.
+ *
+ * If IPIs can go out of order to the cache coherency protocol
+ * in an architecture, sufficient synchronisation should be added
+ * to arch code to make it appear to obey cache coherency WRT
+ * locking and barrier primitives. Generic code isn't really equipped
+ * to do the right thing...
*/
- smp_mb();
if (ipi)
arch_send_call_function_single_ipi(cpu);
@@ -104,6 +111,14 @@ void generic_smp_call_function_interrupt(void)
int cpu = get_cpu();
/*
+ * Ensure entry is visible on call_function_queue after we have
+ * entered the IPI. See comment in smp_call_function_many.
+ * If we don't have this, then we may miss an entry on the list
+ * and never get another IPI to process it.
+ */
+ smp_mb();
+
+ /*
* It's ok to use list_for_each_rcu() here even though we may delete
* 'pos', since list_del_rcu() doesn't clear ->next
*/
@@ -154,49 +169,37 @@ void generic_smp_call_function_single_interrupt(void)
{
struct call_single_queue *q = &__get_cpu_var(call_single_queue);
LIST_HEAD(list);
+ unsigned int data_flags;
- /*
- * Need to see other stores to list head for checking whether
- * list is empty without holding q->lock
- */
- smp_read_barrier_depends();
- while (!list_empty(&q->list)) {
- unsigned int data_flags;
-
- spin_lock(&q->lock);
- list_replace_init(&q->list, &list);
- spin_unlock(&q->lock);
+ spin_lock(&q->lock);
+ list_replace_init(&q->list, &list);
+ spin_unlock(&q->lock);
- while (!list_empty(&list)) {
- struct call_single_data *data;
+ while (!list_empty(&list)) {
+ struct call_single_data *data;
- data = list_entry(list.next, struct call_single_data,
- list);
- list_del(&data->list);
+ data = list_entry(list.next, struct call_single_data,
+ list);
+ list_del(&data->list);
- /*
- * 'data' can be invalid after this call if
- * flags == 0 (when called through
- * generic_exec_single(), so save them away before
- * making the call.
- */
- data_flags = data->flags;
-
- data->func(data->info);
-
- if (data_flags & CSD_FLAG_WAIT) {
- smp_wmb();
- data->flags &= ~CSD_FLAG_WAIT;
- } else if (data_flags & CSD_FLAG_LOCK) {
- smp_wmb();
- data->flags &= ~CSD_FLAG_LOCK;
- } else if (data_flags & CSD_FLAG_ALLOC)
- kfree(data);
- }
/*
- * See comment on outer loop
+ * 'data' can be invalid after this call if
+ * flags == 0 (when called through
+ * generic_exec_single(), so save them away before
+ * making the call.
*/
- smp_read_barrier_depends();
+ data_flags = data->flags;
+
+ data->func(data->info);
+
+ if (data_flags & CSD_FLAG_WAIT) {
+ smp_wmb();
+ data->flags &= ~CSD_FLAG_WAIT;
+ } else if (data_flags & CSD_FLAG_LOCK) {
+ smp_wmb();
+ data->flags &= ~CSD_FLAG_LOCK;
+ } else if (data_flags & CSD_FLAG_ALLOC)
+ kfree(data);
}
}
@@ -375,6 +378,8 @@ void smp_call_function_many(const struct cpumask *mask,
/*
* Make the list addition visible before sending the ipi.
+ * (IPIs must obey or appear to obey normal Linux cache coherency
+ * rules -- see comment in generic_exec_single).
*/
smp_mb();
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