linux-kernel - Re: [PATCH v2 11/24] file: Implement task_lookup_fd

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Message-ID: <20201121181933.GH875895@grain>
Date:   Sat, 21 Nov 2020 21:19:33 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        criu@...nvz.org, bpf@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.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@...radead.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        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 v2 11/24] file: Implement task_lookup_fd_rcu

On Fri, Nov 20, 2020 at 05:14:28PM -0600, Eric W. Biederman wrote:
> 
> diff --git a/fs/file.c b/fs/file.c
> index 5861c4f89419..6448523ca29e 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -865,6 +865,21 @@ struct file *fget_task(struct task_struct *task, unsigned int fd)
>  	return file;
>  }
>  
> +struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd)
> +{
> +	/* Must be called with rcu_read_lock held */

Eric, maybe worth to have something like

	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
			 "suspicious task_lookup_fd_rcu() usage");

here?