Merge branch 'bpf-task_group_seq_get_next-misc-cleanups'

Oleg Nesterov says:

====================
bpf: task_group_seq_get_next: misc cleanups

Yonghong,

I am resending 1-5 of 6 as you suggested with your acks included.

The next (final) patch will change this code to use __next_thread when

	https://lore.kernel.org/all/20230824143142.GA31222@redhat.com/

is merged.

Oleg.
====================

Link: https://lore.kernel.org/r/20230905154612.GA24872@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/task_iter.c

@@ -35,16 +35,13 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
 						   u32 *tid,
 						   bool skip_if_dup_files)
 {
-	struct task_struct *task, *next_task;
+	struct task_struct *task;
 	struct pid *pid;
-	u32 saved_tid;
+	u32 next_tid;
 
 	if (!*tid) {
 		/* The first time, the iterator calls this function. */
 		pid = find_pid_ns(common->pid, common->ns);
-		if (!pid)
-			return NULL;
-
 		task = get_pid_task(pid, PIDTYPE_TGID);
 		if (!task)
 			return NULL;
@@ -66,44 +63,27 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
 		return task;
 	}
 
-	pid = find_pid_ns(common->pid_visiting, common->ns);
-	if (!pid)
-		return NULL;
-
-	task = get_pid_task(pid, PIDTYPE_PID);
+	task = find_task_by_pid_ns(common->pid_visiting, common->ns);
 	if (!task)
 		return NULL;
 
 retry:
-	if (!pid_alive(task)) {
-		put_task_struct(task);
-		return NULL;
-	}
-
-	next_task = next_thread(task);
-	put_task_struct(task);
-	if (!next_task)
-		return NULL;
+	task = next_thread(task);
 
-	saved_tid = *tid;
-	*tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
-	if (!*tid || *tid == common->pid) {
+	next_tid = __task_pid_nr_ns(task, PIDTYPE_PID, common->ns);
+	if (!next_tid || next_tid == common->pid) {
 		/* Run out of tasks of a process.  The tasks of a
 		 * thread_group are linked as circular linked list.
 		 */
-		*tid = saved_tid;
 		return NULL;
 	}
 
-	get_task_struct(next_task);
-	common->pid_visiting = *tid;
-
-	if (skip_if_dup_files && task->files == task->group_leader->files) {
-		task = next_task;
+	if (skip_if_dup_files && task->files == task->group_leader->files)
 		goto retry;
-	}
 
-	return next_task;
+	*tid = common->pid_visiting = next_tid;
+	get_task_struct(task);
+	return task;
 }
 
 static struct task_struct *task_seq_get_next(struct bpf_iter_seq_task_common *common,