linux-kernel - Re: [PATCH 03/13] rust: lock: introduce `Mutex`

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Date:   Mon, 3 Apr 2023 10:20:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        rust-for-linux@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        linux-kernel@...r.kernel.org,
        Wedson Almeida Filho <walmeida@...rosoft.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 03/13] rust: lock: introduce `Mutex`

On Thu, Mar 30, 2023 at 11:47:12AM -0700, Boqun Feng wrote:
> On Thu, Mar 30, 2023 at 03:01:08PM +0200, Peter Zijlstra wrote:
> > On Thu, Mar 30, 2023 at 01:39:44AM -0300, Wedson Almeida Filho wrote:
> > > From: Wedson Almeida Filho <walmeida@...rosoft.com>
> > > 
> > > This is the `struct mutex` lock backend and allows Rust code to use the
> > > kernel mutex idiomatically.
> > 
> > What, if anything, are the plans to support the various lockdep
> > annotations? Idem for the spinlock thing in the other patch I suppose.
> 
> FWIW:
> 
> *	At the init stage, SpinLock and Mutex in Rust use initializers
> 	that are aware of the lockdep, so everything (lockdep_map and
> 	lock_class) is all set up.
> 
> *	At acquire or release time, Rust locks just use ffi to call C
> 	functions that have lockdep annotations in them, so lockdep
> 	should just work.
> 

ffi is what the C++ world calls RAII ?

But yes, I got that far, but I wondered about things like
spin_lock_nested(&foo, SINGLE_DEPTH_NESTING) and other such 'advanced'
annotations.

Surely we're going to be needing them at some point. I suppose you can
do the single depth nesting one with a special guard type (or whatever
you call that in the rust world) ?