Re: [PATCH 3/6] bpf: task_group_seq_get_next: fix the skip_if_dup_files check

[Yonghong Song]

On 8/25/23 10:04 AM, Oleg Nesterov wrote:
> Forgot to mention in the changelog...
>
> In any case this doesn't look right. ->group_leader can exit before other
> threads, call exit_files(), and in this case task_group_seq_get_next() will
> check task->files == NULL.

It is okay. This won't be affecting correctness. We will end with
calling bpf program for 'next_task'.

> On 08/25, Oleg Nesterov wrote:
> > Unless I am notally confused it is wrong. We are going to return or
> > skip next_task so we need to check next_task-files, not task->files.
> >
> > Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> > ---
> >   kernel/bpf/task_iter.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
> > index 1589ec3faded..2264870ae3fc 100644
> > --- a/kernel/bpf/task_iter.c
> > +++ b/kernel/bpf/task_iter.c
> > @@ -82,7 +82,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
> >
> >   	common->pid_visiting = *tid;
> >
> > -	if (skip_if_dup_files && task->files == task->group_leader->files) {
> > +	if (skip_if_dup_files && next_task->files == next_task->group_leader->files) {
> >   		task = next_task;
> >   		goto retry;
> >   	}
> > --
> > 2.25.1.362.g51ebf55