linux-kernel - Re: [PATCH v4 7/9] rust: file: add `Kuid` wrapper

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Date: Fri, 2 Feb 2024 07:36:21 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Carlos Llamas <cmllamas@...gle.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Kees Cook <keescook@...omium.org>,
	Matthew Wilcox <willy@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Daniel Xu <dxu@...uu.xyz>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4 7/9] rust: file: add `Kuid` wrapper

On Fri, Feb 02, 2024 at 10:55:41AM +0000, Alice Ryhl wrote:
> +    /// Returns the given task's pid in the current pid namespace.
> +    pub fn pid_in_current_ns(&self) -> Pid {
> +        let current = Task::current_raw();
> +        // SAFETY: Calling `task_active_pid_ns` with the current task is always safe.
> +        let namespace = unsafe { bindings::task_active_pid_ns(current) };
> +        // SAFETY: We know that `self.0.get()` is valid by the type invariant, and the namespace
> +        // pointer is not dangling since it points at this task's namespace.
> +        unsafe { bindings::task_tgid_nr_ns(self.0.get(), namespace) }
> +    }

pids are reference counted in the kernel, how does this deal with that?
Are they just ignored somehow?  Where is the reference count given back?

thanks,

greg k-h