From: Boqun Feng <boqun.feng@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "Miguel Ojeda" <miguel.ojeda.sandonis@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Peter Zijlstra" <peterz@infradead.org>,
rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
"Will Deacon" <will@kernel.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Miguel Ojeda" <ojeda@kernel.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Vincenzo Palazzo" <vincenzopalazzodev@gmail.com>
Subject: Re: [RFC 2/5] rust: sync: Arc: Introduces ArcInner::count()
Date: Thu, 2 Feb 2023 23:43:23 -0800 [thread overview]
Message-ID: <Y9y7G4AY8MPy5E3r@Boquns-Mac-mini.local> (raw)
In-Reply-To: <Y9y58cy1GKZLdyjb@kroah.com>
On Fri, Feb 03, 2023 at 08:38:25AM +0100, Greg KH wrote:
> On Thu, Feb 02, 2023 at 11:25:08PM -0800, Boqun Feng wrote:
> > On Fri, Feb 03, 2023 at 06:22:15AM +0100, Greg KH wrote:
> > > On Thu, Feb 02, 2023 at 10:47:12PM +0100, Miguel Ojeda wrote:
> > > > On Thu, Feb 2, 2023 at 5:52 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> > > > >
> > > > > As I said, I'm open to remove the printing of the refcount, and if you
> > > > > and Peter think maybe it's OK to do that after the explanation above,
> > > >
> > > > Perhaps part of the confusion came from the overloaded "safe" term.
> > > >
> > > > When Gary and Boqun used the term "safe", they meant it in the Rust
> > > > sense, i.e. calling the method will not allow to introduce undefined
> > > > behavior. While I think Peter and Greg are using the term to mean
> > > > something different.
> > >
> > > Yes, I mean it in a "this is not giving you the value you think you are
> > > getting and you can not rely on it for anything at all as it is going to
> > > be incorrect" meaning.
> > >
> > > Which in kernel code means "this is not something you should do".
> > >
> >
> > Now what really confuses me is why kref_read() is safe..
>
> It isn't, and I hate it and it should be removed from the kernel
> entirely. But the scsi and drm developers seem to insist that "their
> locking model ensures it will be safe to use" and I lost that argument
> :(
>
> > or how this is different than kref_read().
>
> It isn't, but again, I don't like that and do not agree it should be
> used as it is almost always a sign that the logic in the code is
> incorrect.
>
> > Needless to say that ArcInner::count() can guarantee not reading 0
>
> How? Because you have an implicit reference on it already? If so, then
> why does reading from it matter at all, as if you have a reference, you
> know it isn't 0, and that's all that you can really care about. You
> don't care about any number other than 0 for a reference count, as by
> definition, that's what a reference count does :)
>
Fair enough!
> > (because of the type invariants) but kref_read() cannot..
>
> I totally agree with you. Let's not mirror bad decisions of legacy
> subsystems in the kernel written in C with new designs in Rust please.
>
Roger that, will remove this in the next version ;-)
Regards,
Boqun
> thanks,
>
> greg k-h
next prev parent reply other threads:[~2023-02-03 7:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-01 23:22 [RFC 0/5] rust: sync: Arc: Implement Debug and Display Boqun Feng
2023-02-01 23:22 ` [RFC 1/5] rust: sync: impl Display for {Unique,}Arc Boqun Feng
2023-02-02 14:15 ` Gary Guo
2023-02-02 16:50 ` Björn Roy Baron
2023-02-04 10:20 ` Finn Behrens
2023-02-04 18:47 ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 2/5] rust: sync: Arc: Introduces ArcInner::count() Boqun Feng
2023-02-02 9:14 ` Peter Zijlstra
2023-02-02 13:46 ` Boqun Feng
2023-02-02 14:21 ` Gary Guo
2023-02-02 15:41 ` Greg KH
2023-02-02 16:10 ` Boqun Feng
2023-02-02 16:17 ` Greg KH
2023-02-02 16:51 ` Boqun Feng
2023-02-02 21:47 ` Miguel Ojeda
2023-02-03 5:22 ` Greg KH
2023-02-03 7:25 ` Boqun Feng
2023-02-03 7:38 ` Greg KH
2023-02-03 7:43 ` Boqun Feng [this message]
2023-02-03 8:01 ` Boqun Feng
2023-02-03 19:17 ` Josh Stone
2023-02-03 19:22 ` Wedson Almeida Filho
2023-02-02 14:22 ` Gary Guo
2023-02-04 18:48 ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 3/5] rust: sync: Arc: Introduces Arc::get_inner() helper Boqun Feng
2023-02-02 14:24 ` Gary Guo
2023-02-02 16:53 ` Björn Roy Baron
2023-02-04 18:51 ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 4/5] rust: sync: impl Debug for {Unique,}Arc Boqun Feng
2023-02-02 14:28 ` Gary Guo
2023-02-03 19:46 ` Boqun Feng
2023-02-04 18:56 ` Vincenzo Palazzo
2023-02-01 23:22 ` [RFC 5/5] sample: rust: print: Add sampe code for Arc printing Boqun Feng
2023-02-02 16:56 ` Björn Roy Baron
2023-02-04 10:22 ` Finn Behrens
2023-02-04 19:05 ` Vincenzo Palazzo
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