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: Oleg Nesterov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: "Srivatsa S. Bhat" <[email protected]>
Cc: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions