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[103.168.172.200]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b6b5a5b38asm756057285a.27.2024.12.12.09.07.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Dec 2024 09:07:09 -0800 (PST) Received: from phl-compute-05.internal (phl-compute-05.phl.internal [10.202.2.45]) by mailfauth.phl.internal (Postfix) with ESMTP id 6D25F1200066; Thu, 12 Dec 2024 12:07:08 -0500 (EST) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-05.internal (MEProxy); Thu, 12 Dec 2024 12:07:08 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefuddrkeehgdelhecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpggftfghnshhusghstghrihgsvgdpuffr tefokffrpgfnqfghnecuuegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnth hsucdlqddutddtmdenucfjughrpeffhffvvefukfhfgggtugfgjgesthekredttddtjeen ucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrd gtohhmqeenucggtffrrghtthgvrhhnpeegkeegtedtleffkeeftdevleeuieduveejgeei kedvgeekudefteefieeivdeuleenucffohhmrghinhepghhithhhuhgsrdgtohhmnecuve hluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepsghoqhhunhdo mhgvshhmthhprghuthhhphgvrhhsohhnrghlihhthidqieelvdeghedtieegqddujeejke ehheehvddqsghoqhhunhdrfhgvnhhgpeepghhmrghilhdrtghomhesfhhigihmvgdrnhgr mhgvpdhnsggprhgtphhtthhopeehjedpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtoh eprghlihgtvghrhihhlhesghhoohhglhgvrdgtohhmpdhrtghpthhtoheprhhushhtqdhf ohhrqdhlihhnuhigsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtoheprhgtuh esvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehlihhnuhigqdhkvghrnhgv lhesvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehlihhnuhigqdgrrhgthh esvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehllhhvmheslhhishhtshdr lhhinhhugidruggvvhdprhgtphhtthhopehlkhhmmheslhhishhtshdrlhhinhhugidrug gvvhdprhgtphhtthhopehojhgvuggrsehkvghrnhgvlhdrohhrghdprhgtphhtthhopegr lhgvgidrghgrhihnohhrsehgmhgrihhlrdgtohhm X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 12 Dec 2024 12:07:06 -0500 (EST) Date: Thu, 12 Dec 2024 09:07:00 -0800 From: Boqun Feng To: Alice Ryhl Cc: rust-for-linux@vger.kernel.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, llvm@lists.linux.dev, lkmm@lists.linux.dev, Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alan Stern , Andrea Parri , Will Deacon , Peter Zijlstra , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , Daniel Lustig , Joel Fernandes , Nathan Chancellor , Nick Desaulniers , kent.overstreet@gmail.com, Greg Kroah-Hartman , elver@google.com, Mark Rutland , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Catalin Marinas , torvalds@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, Trevor Gross , dakr@redhat.com, Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org Subject: Re: [RFC v2 02/13] rust: sync: Add basic atomic operation mapping framework Message-ID: References: <20241101060237.1185533-1-boqun.feng@gmail.com> <20241101060237.1185533-3-boqun.feng@gmail.com> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu, Dec 12, 2024 at 11:51:23AM +0100, Alice Ryhl wrote: > On Fri, Nov 1, 2024 at 7:03 AM Boqun Feng wrote: > > > > Preparation for generic atomic implementation. To unify the > > ipmlementation of a generic method over `i32` and `i64`, the C side > > atomic methods need to be grouped so that in a generic method, they can > > be referred as ::, otherwise their parameters and return > > value are different between `i32` and `i64`, which would require using > > `transmute()` to unify the type into a `T`. > > > > Introduce `AtomicIpml` to represent a basic type in Rust that has the > > direct mapping to an atomic implementation from C. This trait is sealed, > > and currently only `i32` and `i64` ipml this. > > There seems to be quite a few instances of "impl" spelled as "ipml" here. > Will fix! > > Further, different methods are put into different `*Ops` trait groups, > > and this is for the future when smaller types like `i8`/`i16` are > > supported but only with a limited set of API (e.g. only set(), load(), > > xchg() and cmpxchg(), no add() or sub() etc). > > > > While the atomic mod is introduced, documentation is also added for > > memory models and data races. > > > > Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect > > my responsiblity on the Rust atomic mod. > > > > Signed-off-by: Boqun Feng > > --- > > MAINTAINERS | 4 +- > > rust/kernel/sync.rs | 1 + > > rust/kernel/sync/atomic.rs | 19 ++++ > > rust/kernel/sync/atomic/ops.rs | 199 +++++++++++++++++++++++++++++++++ > > 4 files changed, 222 insertions(+), 1 deletion(-) > > create mode 100644 rust/kernel/sync/atomic.rs > > create mode 100644 rust/kernel/sync/atomic/ops.rs > > > > diff --git a/MAINTAINERS b/MAINTAINERS > > index b77f4495dcf4..e09471027a63 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -3635,7 +3635,7 @@ F: drivers/input/touchscreen/atmel_mxt_ts.c > > ATOMIC INFRASTRUCTURE > > M: Will Deacon > > M: Peter Zijlstra > > -R: Boqun Feng > > +M: Boqun Feng > > R: Mark Rutland > > L: linux-kernel@vger.kernel.org > > S: Maintained > > @@ -3644,6 +3644,8 @@ F: arch/*/include/asm/atomic*.h > > F: include/*/atomic*.h > > F: include/linux/refcount.h > > F: scripts/atomic/ > > +F: rust/kernel/sync/atomic.rs > > +F: rust/kernel/sync/atomic/ > > This is why mod.rs files are superior :) > ;-) Not going to do anything right now, but let me think about this. > > @@ -0,0 +1,19 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +//! Atomic primitives. > > +//! > > +//! These primitives have the same semantics as their C counterparts: and the precise definitions of > > +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory (Consistency) Model is the > > +//! only model for Rust code in kernel, and Rust's own atomics should be avoided. > > +//! > > +//! # Data races > > +//! > > +//! [`LKMM`] atomics have different rules regarding data races: > > +//! > > +//! - A normal read doesn't data-race with an atomic read. > > This was fixed: > https://github.com/rust-lang/rust/pull/128778 > Yeah, I was aware of that effort, and good to know it's finally merged. Thanks! This will be in 1.83, right? If so, we will still need the above until we bump up the minimal rustc version to 1.83 or beyond. I will handle this properly with the minimal rustc 1.83 (i.e. if this goes in first, will send a follow up patch). I will also mention in the above that this has been changed in 1.83. This also reminds that I should add that LKMM allows mixed-size atomic accesses (as non data race), I will add that in the version. > > +mod private { > > + /// Sealed trait marker to disable customized impls on atomic implementation traits. > > + pub trait Sealed {} > > +} > > Just make the trait unsafe? > And make the safety requirement of `AtomicImpl` something like: The type must have the implementation for atomic operations. ? Hmm.. I don't think that's a good safety requirement TBH. Actually the reason that we need to restrict `AtomicImpl` types is more of an iplementation issue (the implementation need to be done if we want to support i8 or i16) rather than safety issue. So a sealed trait is proper here. Does this make sense? Or am I missing something? Regards, Boqun > Alice