On Sun, 2022-08-14 at 22:24 +0200, Jiri Olsa wrote:
> On Wed, Aug 10, 2022 at 05:16:52PM -0700, Kui-Feng Lee wrote:
>
> SNIP
>
> > +static int bpf_iter_attach_task(struct bpf_prog *prog,
> > + union bpf_iter_link_info *linfo,
> > + struct bpf_iter_aux_info *aux)
> > +{
> > + unsigned int flags;
> > + struct pid_namespace *ns;
> > + struct pid *pid;
> > + pid_t tgid;
> > +
> > + if (linfo->task.tid != 0) {
> > + aux->task.type = BPF_TASK_ITER_TID;
> > + aux->task.tid = linfo->task.tid;
> > + } else if (linfo->task.tgid != 0) {
> > + aux->task.type = BPF_TASK_ITER_TGID;
> > + aux->task.tgid = linfo->task.tgid;
> > + } else if (linfo->task.pid_fd != 0) {
> > + aux->task.type = BPF_TASK_ITER_TGID;
> > + pid = pidfd_get_pid(linfo->task.pid_fd, &flags);
> > + if (IS_ERR(pid))
> > + return PTR_ERR(pid);
> > +
> > + ns = task_active_pid_ns(current);
> > + if (IS_ERR(ns))
> > + return PTR_ERR(ns);
> > +
> > + tgid = pid_nr_ns(pid, ns);
> > + if (tgid <= 0)
> > + return -EINVAL;
> > +
> > + aux->task.tgid = tgid;
> > + } else {
> > + aux->task.type = BPF_TASK_ITER_ALL;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > static const struct seq_operations task_seq_ops = {
> > .start = task_seq_start,
> > .next = task_seq_next,
> > @@ -137,8 +198,7 @@ struct bpf_iter_seq_task_file_info {
> > static struct file *
> > task_file_seq_get_next(struct bpf_iter_seq_task_file_info *info)
> > {
> > - struct pid_namespace *ns = info->common.ns;
> > - u32 curr_tid = info->tid;
> > + u32 saved_tid = info->tid;
>
> we use 'curr_' prefix for other stuff in the function, like
> curr_task, curr_fd .. I think we should either change all of
> them or actually keep curr_tid, which seem better to me
The purpose of the variable is changed, so I think 'curr_tid' is not
feasible anymore. It was the tid of the task that we are visiting.
But, now, it is the tid of the task that the iterator was visiting
when/before entering the function. In this patch, info->tid is always
the value of the current visiting task.
>
> jirka
>
> > struct task_struct *curr_task;
> > unsigned int curr_fd = info->fd;
> >
> > @@ -151,21 +211,18 @@ task_file_seq_get_next(struct
> > bpf_iter_seq_task_file_info *info)
> > curr_task = info->task;
> > curr_fd = info->fd;
> > } else {
> > - curr_task = task_seq_get_next(ns, &curr_tid,
> > true);
> > + curr_task = task_seq_get_next(&info->common, &info-
> > >tid, true);
> > if (!curr_task) {
> > info->task = NULL;
> > - info->tid = curr_tid;
> > return NULL;
> > }
> >
> > - /* set info->task and info->tid */
> > + /* set info->task */
> > info->task = curr_task;
> > - if (curr_tid == info->tid) {
> > + if (saved_tid == info->tid)
> > curr_fd = info->fd;
> > - } else {
> > - info->tid = curr_tid;
> > + else
> > curr_fd = 0;
> > - }
> > }
> >
>
> SNIP
