Messages in this thread Patch in this message | | | Date | Mon, 11 Mar 2013 18:36:43 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 1/2] kthread: introduce to_live_kthread() |
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"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 <oleg@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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