On Fri, Dec 18, 2020 at 12:47 PM Jonathan Lemon
<jonathan.lemon@xxxxxxxxx> wrote:
>
> From: Jonathan Lemon <bsd@xxxxxx>
>
> Only obtain the task reference count at the end of the RCU section
> instead of repeatedly obtaining/releasing it when iterating though
> a thread group.
>
> Jump to the correct branch when it is known that the task is NULL.
>
> Signed-off-by: Jonathan Lemon <jonathan.lemon@xxxxxxxxx>
> ---
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> kernel/bpf/task_iter.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> index dc4007f1843b..598a8d7da5bf 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -33,7 +33,7 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
> pid = find_ge_pid(*tid, ns);
> if (pid) {
> *tid = pid_nr_ns(pid, ns);
> - task = get_pid_task(pid, PIDTYPE_PID);
> + task = pid_task(pid, PIDTYPE_PID);
> if (!task) {
> ++*tid;
> goto retry;
> @@ -44,6 +44,7 @@ static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
> ++*tid;
> goto retry;
> }
> + get_task_struct(task);
> }
> rcu_read_unlock();
>
> @@ -148,12 +149,12 @@ task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
> * it held a reference to the task/files_struct/file.
> * Otherwise, it does not hold any reference.
> */
> -again:
> if (info->task) {
> curr_task = info->task;
> curr_files = info->files;
> curr_fd = info->fd;
> } else {
> +again:
> curr_task = task_seq_get_next(ns, &curr_tid, true);
> if (!curr_task) {
> info->task = NULL;
> --
> 2.24.1
>
