generic-ipi: remove CSD_FLAG_WAIT
Oleg noticed that we don't strictly need CSD_FLAG_WAIT, rework
the code so that we can use CSD_FLAG_LOCK for both purposes.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/smp.c b/kernel/smp.c
index 7a0ce25..f530825 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -23,8 +23,7 @@
};
enum {
- CSD_FLAG_WAIT = 0x01,
- CSD_FLAG_LOCK = 0x02,
+ CSD_FLAG_LOCK = 0x01,
};
struct call_function_data {
@@ -95,41 +94,21 @@
early_initcall(init_call_single_data);
/*
- * csd_wait/csd_complete are used for synchronous ipi calls
- */
-static void csd_wait_prepare(struct call_single_data *data)
-{
- data->flags |= CSD_FLAG_WAIT;
-}
-
-static void csd_complete(struct call_single_data *data)
-{
- if (data->flags & CSD_FLAG_WAIT) {
- /*
- * ensure we're all done before saying we are
- */
- smp_mb();
- data->flags &= ~CSD_FLAG_WAIT;
- }
-}
-
-static void csd_wait(struct call_single_data *data)
-{
- while (data->flags & CSD_FLAG_WAIT)
- cpu_relax();
-}
-
-/*
* csd_lock/csd_unlock used to serialize access to per-cpu csd resources
*
* For non-synchronous ipi calls the csd can still be in use by the previous
* function call. For multi-cpu calls its even more interesting as we'll have
* to ensure no other cpu is observing our csd.
*/
-static void csd_lock(struct call_single_data *data)
+static void csd_lock_wait(struct call_single_data *data)
{
while (data->flags & CSD_FLAG_LOCK)
cpu_relax();
+}
+
+static void csd_lock(struct call_single_data *data)
+{
+ csd_lock_wait(data);
data->flags = CSD_FLAG_LOCK;
/*
@@ -155,11 +134,12 @@
* Insert a previously allocated call_single_data element for execution
* on the given CPU. data must already have ->func, ->info, and ->flags set.
*/
-static void generic_exec_single(int cpu, struct call_single_data *data)
+static
+void generic_exec_single(int cpu, struct call_single_data *data, int wait)
{
struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
- int wait = data->flags & CSD_FLAG_WAIT, ipi;
unsigned long flags;
+ int ipi;
spin_lock_irqsave(&dst->lock, flags);
ipi = list_empty(&dst->list);
@@ -182,7 +162,7 @@
arch_send_call_function_single_ipi(cpu);
if (wait)
- csd_wait(data);
+ csd_lock_wait(data);
}
/*
@@ -232,7 +212,6 @@
if (refs)
continue;
- csd_complete(&data->csd);
csd_unlock(&data->csd);
}
@@ -270,9 +249,6 @@
data->func(data->info);
- if (data_flags & CSD_FLAG_WAIT)
- csd_complete(data);
-
/*
* Unlocked CSDs are valid through generic_exec_single()
*/
@@ -313,36 +289,16 @@
func(info);
local_irq_restore(flags);
} else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
- struct call_single_data *data;
+ struct call_single_data *data = &d;
- if (!wait) {
- /*
- * We are calling a function on a single CPU
- * and we are not going to wait for it to finish.
- * We use a per cpu data to pass the information to
- * that CPU. Since all callers of this code will
- * use the same data, we must synchronize the
- * callers to prevent a new caller from corrupting
- * the data before the callee can access it.
- *
- * The CSD_FLAG_LOCK is used to let us know when
- * the IPI handler is done with the data.
- * The first caller will set it, and the callee
- * will clear it. The next caller must wait for
- * it to clear before we set it again. This
- * will make sure the callee is done with the
- * data before a new caller will use it.
- */
+ if (!wait)
data = &__get_cpu_var(csd_data);
- csd_lock(data);
- } else {
- data = &d;
- csd_wait_prepare(data);
- }
+
+ csd_lock(data);
data->func = func;
data->info = info;
- generic_exec_single(cpu, data);
+ generic_exec_single(cpu, data, wait);
} else {
err = -ENXIO; /* CPU not online */
}
@@ -362,12 +318,15 @@
* instance.
*
*/
-void __smp_call_function_single(int cpu, struct call_single_data *data)
+void __smp_call_function_single(int cpu, struct call_single_data *data,
+ int wait)
{
- /* Can deadlock when called with interrupts disabled */
- WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
+ csd_lock(data);
- generic_exec_single(cpu, data);
+ /* Can deadlock when called with interrupts disabled */
+ WARN_ON(wait && irqs_disabled());
+
+ generic_exec_single(cpu, data, wait);
}
/* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
@@ -425,9 +384,6 @@
csd_lock(&data->csd);
spin_lock_irqsave(&data->lock, flags);
- if (wait)
- csd_wait_prepare(&data->csd);
-
data->csd.func = func;
data->csd.info = info;
cpumask_and(data->cpumask, mask, cpu_online_mask);
@@ -456,7 +412,7 @@
/* optionally wait for the CPUs to complete */
if (wait)
- csd_wait(&data->csd);
+ csd_lock_wait(&data->csd);
}
EXPORT_SYMBOL(smp_call_function_many);