"k->vfork_done != NULL" with a barrier() after to_kthread(k) in
task_get_live_kthread(k) looks unclear, and sub-optimal because
we load ->vfork_done twice.
All we need is to ensure that we do not return to_kthread(NULL).
Add a new trivial helper which loads/checks ->vfork_done once,
this also looks more understandable.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/kthread.c | 26 ++++++++++++++++----------
1 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 691dc2e..fa4a013 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -52,8 +52,21 @@ enum KTHREAD_BITS {
KTHREAD_IS_PARKED,
};
-#define to_kthread(tsk) \
- container_of((tsk)->vfork_done, struct kthread, exited)
+#define __to_kthread(vfork) \
+ container_of(vfork, struct kthread, exited)
+
+static inline struct kthread *to_kthread(struct task_struct *k)
+{
+ return __to_kthread(k->vfork_done);
+}
+
+static struct kthread *to_live_kthread(struct task_struct *k)
+{
+ struct completion *vfork = ACCESS_ONCE(k->vfork_done);
+ if (likely(vfork))
+ return __to_kthread(vfork);
+ return NULL;
+}
/**
* kthread_should_stop - should this kthread return now?
@@ -313,15 +326,8 @@ struct task_struct *kthread_create_on_cpu(int
(*threadfn)(void *data),
static struct kthread *task_get_live_kthread(struct task_struct *k)
{
- struct kthread *kthread;
-
get_task_struct(k);
- kthread = to_kthread(k);
- /* It might have exited */
- barrier();
- if (k->vfork_done != NULL)
- return kthread;
- return NULL;
+ return to_live_kthread(k);
}
/**
--
1.5.5.1
--
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