linux-kernel - Re: [PATCH v10 1/8] rust: types: add `NotThreadSafe`

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Message-ID: <20240925135904.GA654417@mail.hallyn.com>
Date: Wed, 25 Sep 2024 08:59:04 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: "Serge E. Hallyn" <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>, Miguel Ojeda <ojeda@...nel.org>,
	Christian Brauner <brauner@...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>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.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>,
	Matthew Wilcox <willy@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Daniel Xu <dxu@...uu.xyz>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v10 1/8] rust: types: add `NotThreadSafe`

On Wed, Sep 25, 2024 at 01:06:10PM +0200, Alice Ryhl wrote:
> On Tue, Sep 24, 2024 at 9:45 PM Serge E. Hallyn <serge@...lyn.com> wrote:
> >
> > On Sun, Sep 15, 2024 at 02:31:27PM +0000, Alice Ryhl wrote:
> > > This introduces a new marker type for types that shouldn't be thread
> > > safe. By adding a field of this type to a struct, it becomes non-Send
> > > and non-Sync, which means that it cannot be accessed in any way from
> > > threads other than the one it was created on.
> > >
> > > This is useful for APIs that require globals such as `current` to remain
> > > constant while the value exists.
> > >
> > > We update two existing users in the Kernel to use this helper:
> > >
> > >  * `Task::current()` - moving the return type of this value to a
> > >    different thread would not be safe as you can no longer be guaranteed
> > >    that the `current` pointer remains valid.
> > >  * Lock guards. Mutexes and spinlocks should be unlocked on the same
> > >    thread as where they were locked, so we enforce this using the Send
> > >    trait.
> >
> > Hi,
> >
> > this sounds useful, however from kernel side when I think thread-safe,
> > I think must not be used across a sleep.  Would something like ThreadLocked
> > or LockedToThread make sense?
> 
> Hmm, those names seem pretty similar to the current name to me?

Seems very different to me:

If @foo is not threadsafe, it may be global or be usable by many
threads, but must be locked to one thread during access.

What you're describing here is (iiuc) that @foo must only be used
by one particular thread.

-serge