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Commit 4ecdafc8 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

kthread: introduce to_live_kthread() 



"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: default avatarOleg 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ec25e246

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)