Re: [RFC PATCH bpf-next 08/16] bpf: add task and task/file targets

Alexei Starovoitov
2020-04-10T03:22:29Z

On Wed, Apr 08, 2020 at 04:25:29PM -0700, Yonghong Song wrote:
> +
> + spin_lock(&files->file_lock);
> + for (; sfd < files_fdtable(files)->max_fds; sfd++) {
> + struct file *f;
> +
> + f = fcheck_files(files, sfd);
> + if (!f)
> + continue;
> +
> + *fd = sfd;
> + get_file(f);
> + spin_unlock(&files->file_lock);
> + return f;
> + }
> +
> + /* the current task is done, go to the next task */
> + spin_unlock(&files->file_lock);
> + put_files_struct(files);

I think spin_lock is unnecessary.
It's similarly unnecessary in bpf_task_fd_query().
Take a look at proc_readfd_common() in fs/proc/fd.c.
It only needs rcu_read_lock() to iterate fd array.