On Thu, Apr 15, 2021 at 9:27 PM Boqun Feng <boqun.feng@xxxxxxxxx> wrote: > > [Copy LKMM people, Josh, Nick and Wedson] > > On Thu, Apr 15, 2021 at 08:58:16PM +0200, Peter Zijlstra wrote: > > On Wed, Apr 14, 2021 at 08:45:51PM +0200, ojeda@xxxxxxxxxx wrote: > > > > > Rust is a systems programming language that brings several key > > > advantages over C in the context of the Linux kernel: > > > > > > - No undefined behavior in the safe subset (when unsafe code is > > > sound), including memory safety and the absence of data races. > > > > And yet I see not a single mention of the Rust Memory Model and how it > > aligns (or not) with the LKMM. The C11 memory model for example is a > > really poor fit for LKMM. > > > > I think Rust currently uses C11 memory model as per: > > https://doc.rust-lang.org/nomicon/atomics.html > > , also I guess another reason that they pick C11 memory model is because > LLVM has the support by default. > > But I think the Rust Community still wants to have a good memory model, > and they are open to any kind of suggestion and input. I think we (LKMM > people) should really get involved, because the recent discussion on > RISC-V's atomics shows that if we didn't people might get a "broken" > design because they thought C11 memory model is good enough: > > https://lore.kernel.org/lkml/YGyZPCxJYGOvqYZQ@boqun-archlinux/ > > And the benefits are mutual: a) Linux Kernel Memory Model (LKMM) is > defined by combining the requirements of developers and the behavior of > hardwares, it's pratical and can be a very good input for memory model > designing in Rust; b) Once Rust has a better memory model, the compiler > technologies whatever Rust compilers use to suppor the memory model can > be adopted to C compilers and we can get that part for free. Yes, I agree; I think that's a very good approach. Avoiding the ISO WG14 is interesting; at least the merits could be debated in the public and not behind closed doors. > > At least I personally is very intereted to help Rust on a complete and > pratical memory model ;-) > > Josh, I think it's good if we can connect to the people working on Rust > memoryg model, I think the right person is Ralf Jung and the right place > is https://github.com/rust-lang/unsafe-code-guidelines, but you > cerntainly know better than me ;-) Or maybe we can use Rust-for-Linux or > linux-toolchains list to discuss. > > [...] > > > - Boqun Feng is working hard on the different options for > > > threading abstractions and has reviewed most of the `sync` PRs. > > > > Boqun, I know you're familiar with LKMM, can you please talk about how > > Rust does things and how it interacts? > > As Wedson said in the other email, currently there is no code requiring > synchronization between C side and Rust side, so we are currently fine. > But in the longer term, we need to teach Rust memory model about the > "design patterns" used in Linux kernel for parallel programming. > > What I have been doing so far is reviewing patches which have memory > orderings in Rust-for-Linux project, try to make sure we don't include > memory ordering bugs for the beginning. > > Regards, > Boqun -- Thanks, ~Nick Desaulniers
