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

From: Yonghong Song <yonghong.song@linux.dev>
To: Oleg Nesterov <oleg@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yonghong Song <yhs@fb.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kui-Feng Lee <kuifeng@fb.com>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@kernel.org>,
	bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/6] bpf: task_group_seq_get_next: fix the skip_if_dup_files check
Date: Fri, 25 Aug 2023 15:49:35 -0700	[thread overview]
Message-ID: <344aad78-c664-728c-44f1-e00373c8579c@linux.dev> (raw)
In-Reply-To: <20230825161947.GA16871@redhat.com>

On 8/25/23 9:19 AM, 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.

Thanks for capturing this. This is indeed an oversight.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>   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;
>   	}