linux-kernel - Re: [PATCH] fs/pipe: Fix lockdep false-positive in watchqueue pipe

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Date:   Fri, 24 Nov 2023 15:53:47 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     dhowells@...hat.com, Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] fs/pipe: Fix lockdep false-positive in watchqueue pipe_write()

Jann Horn <jannh@...gle.com> wrote:

> +	/*
> +	 * Reject writing to watch queue pipes before the point where we lock
> +	 * the pipe.
> +	 * Otherwise, lockdep would be unhappy if the caller already has another
> +	 * pipe locked.
> +	 * If we had to support locking a normal pipe and a notification pipe at
> +	 * the same time, we could set up lockdep annotations for that, but
> +	 * since we don't actually need that, it's simpler to just bail here.
> +	 */
> +	if (pipe_has_watch_queue(pipe))
> +		return -EXDEV;
> +

Linus wanted it to be possible for the user to write to a notificaiton pipe.

David