linux-kernel - Re: [PATCH 09/17] file: Implement fnext

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Message-ID: <CAADnVQKpDaaogmbZPD0bv3SrTXo9i5eSBMz1dd=3wOn9pxDOWA@mail.gmail.com>
Date:   Wed, 19 Aug 2020 08:54:50 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>,
        criu@...nvz.org, bpf <bpf@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...ian.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Matthew Wilcox <matthew@....cx>,
        Trond Myklebust <trond.myklebust@....uio.no>,
        Chris Wright <chrisw@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH 09/17] file: Implement fnext_task

On Wed, Aug 19, 2020 at 6:25 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> The bug in the existing code is that bpf_iter does get_file instead
> of get_file_rcu.  Does anyone have any sense of how to add debugging
> to get_file to notice when it is being called in the wrong context?

That bug is already fixed in bpf tree.
See commit cf28f3bbfca0 ("bpf: Use get_file_rcu() instead of
get_file() for task_file iterator")