kthread: introduce to_live_kthread() (4ecdafc8) · Commits · 戴 / test

"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> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Namhyung Kim <namhyung@kernel.org> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> Cc: Tejun Heo <tj@kernel.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/kthread.c

+16 −10

Original line number	Diff line number	Diff line
		@@ -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);
		}

		static void __kthread_unpark(struct task_struct k, struct kthread kthread)

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