[PATCH 5/8] introduce find_get_task_by_vpid()

[Oleg Nesterov <oleg@redhat.com>]

Introduce the new helper, find_get_task_by_vpid(), which simply
does find_task_by_vpid() + get_task_struct() under rcu_read_lock().

It has several potential users which currently do this by hand,
and we are going to add clone_vfork_restart() which needs it too.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 include/linux/sched.h |    1 +
 kernel/pid.c          |   13 +++++++++++++
 2 files changed, 14 insertions(+)

--- 3.1/include/linux/sched.h~5_find_get_task	2011-07-26 20:35:55.000000000 +0200
+++ 3.1/include/linux/sched.h	2011-07-26 20:36:10.000000000 +0200
@@ -2107,6 +2107,7 @@ extern struct pid_namespace init_pid_ns;
  */
 
 extern struct task_struct *find_task_by_vpid(pid_t nr);
+extern struct task_struct *find_get_task_by_vpid(pid_t vnr);
 extern struct task_struct *find_task_by_pid_ns(pid_t nr,
 		struct pid_namespace *ns);
 
--- 3.1/kernel/pid.c~5_find_get_task	2011-07-26 15:50:15.000000000 +0200
+++ 3.1/kernel/pid.c	2011-07-26 20:33:18.000000000 +0200
@@ -427,6 +427,19 @@ struct task_struct *find_task_by_vpid(pi
 	return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns);
 }
 
+struct task_struct *find_get_task_by_vpid(pid_t vnr)
+{
+	struct task_struct *task;
+
+	rcu_read_lock();
+	task = find_task_by_vpid(vnr);
+	if (task)
+		get_task_struct(task);
+	rcu_read_unlock();
+
+	return task;
+}
+
 struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
 {
 	struct pid *pid;