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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20231124150822.2121798-1-jannh@google.com>
References: <20231124150822.2121798-1-jannh@google.com>
To:     Jann Horn <jannh@google.com>
Cc:     dhowells@redhat.com, Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
Subject: Re: [PATCH] fs/pipe: Fix lockdep false-positive in watchqueue pipe_write()
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Content-ID: <1210482.1700841227.1@warthog.procyon.org.uk>
Date:   Fri, 24 Nov 2023 15:53:47 +0000
Message-ID: <1210483.1700841227@warthog.procyon.org.uk>
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Jann Horn <jannh@google.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