exit: hoist get_pid() in release_task() outside of tasklist_lock

Reduces hold time as get_pid() contains an atomic.

Reviewed-by: Oleg Nesterov <[email protected]>
Signed-off-by: Mateusz Guzik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: "Liam R. Howlett" <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: mjguzik

kernel/exit.c

@@ -240,9 +240,10 @@ void release_task(struct task_struct *p)
 
 	cgroup_release(p);
 
+	thread_pid = get_pid(p->thread_pid);
+
 	write_lock_irq(&tasklist_lock);
 	ptrace_release_task(p);
-	thread_pid = get_pid(p->thread_pid);
 	__exit_signal(p);
 
 	/*