bpf: task_group_seq_get_next: cleanup the usage of get/put_task_struct

get_pid_task() makes no sense, the code does put_task_struct() soon after.
Use find_task_by_pid_ns() instead of find_pid_ns + get_pid_task and kill
put_task_struct(), this allows to do get_task_struct() only once before
return.

While at it, kill the unnecessary "if (!pid)" check in the "if (!*tid)"
block, this matches the next usage of find_pid_ns() + get_pid_task() in
this function.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230905154649.GA24935@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 4d112510801410759b19e0afe2cf58b7d2a91cfd..1589ec3faded87642de0ec49822d889dafff0dad 100644 (file)
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -42,9 +42,6 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
        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;
@@ -66,17 +63,12 @@ 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:
        next_task = next_thread(task);
-       put_task_struct(task);
 
        saved_tid = *tid;
        *tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
@@ -88,7 +80,6 @@ retry:
                return NULL;
        }
 
-       get_task_struct(next_task);
        common->pid_visiting = *tid;
 
        if (skip_if_dup_files && task->files == task->group_leader->files) {
@@ -96,6 +87,7 @@ retry:
                goto retry;
        }
 
+       get_task_struct(next_task);
        return next_task;
 }