Use find_task_by_pid_ns() in places that operate with virtual pids

When the pid comes from the userspace, the find_task_by_pid_ns() should be used to find the task by pid in particular (usually the current) namespace. These places were lost in earlier patches.

Think over: all these places work like this:

	if (pid == 0)
		task = current;
	else
		task = find_task_by_pid_ns(pid);

the question is: does it worth introducing a common helper for such case and (if it does) what should its name be?

---

This is a lost hunks of the -mm patch named pid-namespaces-changes-to-show-virtual-ids-to-user.patch

fs/ioprio.c           |    6 ++++--
kernel/futex.c        |    6 ++++--
kernel/futex_compat.c |    3 ++-
kernel/sched.c        |    3 ++-
mm/mempolicy.c        |    3 ++-
mm/migrate.c          |    3 ++-
6 files changed, 16 insertions(+), 8 deletions(-)

index c99fe7b..0a615f8 100644
@@ -94,7 +94,8 @@ asmlinkage long sys_ioprio_set(int which

			if (!who)
				p = current;
			else
-				p = find_task_by_pid(who);
+				p = find_task_by_pid_ns(who,
+						current->nsproxy->pid_ns);
			if (p)
				ret = set_task_ioprio(p, ioprio);
			break;
@@ -181,7 +182,8 @@ asmlinkage long sys_ioprio_get(int which
			if (!who)
				p = current;
			else
-				p = find_task_by_pid(who);
+				p = find_task_by_pid_ns(who,
+						current->nsproxy->pid_ns);
			if (p)
				ret = get_task_ioprio(p);
			break;

index c61634a..0c1b777 100644
@@ -444,7 +444,8 @@ static struct task_struct * futex_find_g

	struct task_struct *p;

	rcu_read_lock();

- p = find_task_by_pid(pid);
+ p = find_task_by_pid_ns(pid,
+ current->nsproxy->pid_ns);

	if (!p || ((current->euid != p->euid) && (current->euid != p->uid)))
		p = ERR_PTR(-ESRCH);

@@ -1855,7 +1856,8 @@ sys_get_robust_list(int pid, struct robu

		ret = -ESRCH;
		rcu_read_lock();
-		p = find_task_by_pid(pid);
+		p = find_task_by_pid_ns(pid,
+				current->nsproxy->pid_ns);
		if (!p)
			goto err_unlock;
		ret = -EPERM;

index f792136..e7563bf 100644
@@ -116,7 +116,8 @@ compat_sys_get_robust_list(int pid, comp
 

		ret = -ESRCH;
		read_lock(&tasklist_lock);
-		p = find_task_by_pid(pid);
+		p = find_task_by_pid_ns(pid,
+				current->nsproxy->pid_ns);
		if (!p)
			goto err_unlock;
		ret = -EPERM;

index 4359b6b..1f81803 100644
@@ -4108,7 +4108,8 @@ struct task_struct *idle_task(int cpu)
 */

static inline struct task_struct *find_process_by_pid(pid_t pid) {
- return pid ? find_task_by_pid(pid) : current;
+ return pid ?
+ find_task_by_pid_ns(pid, current->nsproxy->pid_ns) : current;
}

/* Actually do priority change: must hold rq lock. */

index e7eb2bb..934abc9 100644
@@ -930,7 +930,8 @@ asmlinkage long sys_migrate_pages(pid_t 
 

	/* Find the mm_struct */
	read_lock(&tasklist_lock);
-	task = pid ? find_task_by_pid(pid) : current;
+	task = pid ?
+		find_task_by_pid_ns(pid, current->nsproxy->pid_ns) : current;
	if (!task) {
		read_unlock(&tasklist_lock);
		return -ESRCH;

index 477b894..7f43c5f 100644
@@ -917,7 +917,8 @@ asmlinkage long sys_move_pages(pid_t pid
 

	/* Find the mm_struct */
	read_lock(&tasklist_lock);
-	task = pid ? find_task_by_pid(pid) : current;
+	task = pid ?
+		find_task_by_pid_ns(pid, current->nsproxy->pid_ns) : current;
	if (!task) {
		read_unlock(&tasklist_lock);
		return -ESRCH;