--- kernel/smp.c
+++ kernel/smp.c
@@ -388,7 +388,7 @@ void smp_call_function_many(const struct
{
struct call_function_data *data;
unsigned long flags;
- int refs, cpu, next_cpu, this_cpu = smp_processor_id();
+ int cpu, next_cpu, this_cpu = smp_processor_id();
/*
* Can deadlock when called with interrupts disabled.
@@ -399,7 +399,7 @@ void smp_call_function_many(const struct
WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
&& !oops_in_progress);
- /* Try to fastpath. So, what's a CPU they want? Ignoring this one. */
+ /* So, what's a CPU they want? Ignoring this one. */
cpu = cpumask_first_and(mask, cpu_online_mask);
if (cpu == this_cpu)
cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
@@ -421,49 +421,22 @@ void smp_call_function_many(const struct
data = &__get_cpu_var(cfd_data);
csd_lock(&data->csd);
-
- /* This BUG_ON verifies our reuse assertions and can be removed */
BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask));
- /*
- * The global call function queue list add and delete are protected
- * by a lock, but the list is traversed without any lock, relying
- * on the rcu list add and delete to allow safe concurrent traversal.
- * We reuse the call function data without waiting for any grace
- * period after some other cpu removes it from the global queue.
- * This means a cpu might find our data block as it is being
- * filled out.
- *
- * We hold off the interrupt handler on the other cpu by
- * ordering our writes to the cpu mask vs our setting of the
- * refs counter. We assert only the cpu owning the data block
- * will set a bit in cpumask, and each bit will only be cleared
- * by the subject cpu. Each cpu must first find its bit is
- * set and then check that refs is set indicating the element is
- * ready to be processed, otherwise it must skip the entry.
- *
- * On the previous iteration refs was set to 0 by another cpu.
- * To avoid the use of transitivity, set the counter to 0 here
- * so the wmb will pair with the rmb in the interrupt handler.
- */
- atomic_set(&data->refs, 0); /* convert 3rd to 1st party write */
-
data->csd.func = func;
data->csd.info = info;
-
- /* Ensure 0 refs is visible before mask. Also orders func and info */
- smp_wmb();
-
- /* We rely on the "and" being processed before the store */
cpumask_and(data->cpumask, mask, cpu_online_mask);
cpumask_clear_cpu(this_cpu, data->cpumask);
- refs = cpumask_weight(data->cpumask);
- /* Some callers race with other cpus changing the passed mask */
- if (unlikely(!refs)) {
- csd_unlock(&data->csd);
- return;
- }
+ /*
+ * To ensure the interrupt handler gets an complete view
+ * we order the cpumask and refs writes and order the read
+ * of them in the interrupt handler. In addition we may
+ * only clear our own cpu bit from the mask.
+ */
+ smp_wmb();
+
+ atomic_set(&data->refs, cpumask_weight(data->cpumask));
spin_lock_irqsave(&call_function.lock, flags);
/*
@@ -472,12 +445,6 @@ void smp_call_function_many(const struct
* will not miss any other list entries:
*/
list_add_rcu(&data->csd.list, &call_function.queue);
- /*
- * We rely on the wmb() in list_add_rcu to complete our writes
- * to the cpumask before this write to refs, which indicates
- * data is on the list and is ready to be processed.
- */
- atomic_set(&data->refs, refs);
spin_unlock_irqrestore(&call_function.lock, flags);
/*
projects / ziggy471-frankenstein-kernel.git / blobdiff