redefine thread_group_leader() as exit_signal >= 0

Change de_thread() to set old_leader->exit_signal = -1. This is
good for the consistency, it is no longer the leader and all
sub-threads have exit_signal = -1 set by copy_process(CLONE_THREAD).

And this allows us to micro-optimize thread_group_leader(), it can
simply check exit_signal >= 0. This also makes sense because we
should move ->group_leader from task_struct to signal_struct.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 39acee2c8929..b38ed51d5c64 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2284,8 +2284,10 @@ static inline int get_nr_threads(struct task_struct *tsk)
         return tsk->signal->nr_threads;
 }
 
-/* de_thread depends on thread_group_leader not being a pid based check */
-#define thread_group_leader(p)  (p == p->group_leader)
+static inline bool thread_group_leader(struct task_struct *p)
+{
+        return p->exit_signal >= 0;
+}
 
 /* Do to the insanities of de_thread it is possible for a process
  * to have the pid of the thread group leader without actually being