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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d353ff0302sm15846736d6.74.2024.10.31.23.04.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 31 Oct 2024 23:04:07 -0700 (PDT) Received: from phl-compute-03.internal (phl-compute-03.phl.internal [10.202.2.43]) by mailfauth.phl.internal (Postfix) with ESMTP id 8C55F1200043; Fri, 1 Nov 2024 02:04:06 -0400 (EDT) Received: from phl-mailfrontend-02 ([10.202.2.163]) by phl-compute-03.internal (MEProxy); Fri, 01 Nov 2024 02:04:06 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeftddrvdekkedgkeekucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdggtfgfnhhsuhgsshgtrhhisggvpdfu rfetoffkrfgpnffqhgenuceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnh htshculddquddttddmnecujfgurhephffvvefufffkofgjfhgggfestdekredtredttden ucfhrhhomhepuehoqhhunhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrd gtohhmqeenucggtffrrghtthgvrhhnpeegleejiedthedvheeggfejveefjeejkefgveff ieeujefhueeigfegueehgeeggfenucevlhhushhtvghrufhiiigvpedunecurfgrrhgrmh epmhgrihhlfhhrohhmpegsohhquhhnodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhi thihqdeiledvgeehtdeigedqudejjeekheehhedvqdgsohhquhhnrdhfvghngheppehgmh grihhlrdgtohhmsehfihigmhgvrdhnrghmvgdpnhgspghrtghpthhtohepheejpdhmohgu vgepshhmthhpohhuthdprhgtphhtthhopehruhhsthdqfhhorhdqlhhinhhugiesvhhgvg hrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehrtghusehvghgvrhdrkhgvrhhnvghl rdhorhhgpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvg hlrdhorhhgpdhrtghpthhtoheplhhinhhugidqrghrtghhsehvghgvrhdrkhgvrhhnvghl rdhorhhgpdhrtghpthhtoheplhhlvhhmsehlihhsthhsrdhlihhnuhigrdguvghvpdhrtg hpthhtoheplhhkmhhmsehlihhsthhsrdhlihhnuhigrdguvghvpdhrtghpthhtohepohhj vggurgeskhgvrhhnvghlrdhorhhgpdhrtghpthhtoheprghlvgigrdhgrgihnhhorhesgh hmrghilhdrtghomhdprhgtphhtthhopeifvggushhonhgrfhesghhmrghilhdrtghomh X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 1 Nov 2024 02:04:05 -0400 (EDT) From: Boqun Feng To: 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 Cc: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , 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: [RFC v2 10/13] rust: sync: atomic: Add arithmetic ops for Atomic<*mut T> Date: Thu, 31 Oct 2024 23:02:33 -0700 Message-ID: <20241101060237.1185533-11-boqun.feng@gmail.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20241101060237.1185533-1-boqun.feng@gmail.com> References: <20241101060237.1185533-1-boqun.feng@gmail.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (This is more an RFC) Add arithmetic operations support for `Atomic<*mut T>`. Currently the semantics of arithmetic atomic operation is the same as pointer arithmetic, that is, e.g. `Atomic<*mut u64>::add(1)` is adding 8 (`size_of::`) to the pointer value. In Rust std library, there are two sets of pointer arithmetic for `AtomicPtr`: * ptr_add() and ptr_sub(), which is the same as Atomic<*mut T>::add(), pointer arithmetic. * byte_add() and byte_sub(), which use the input as byte offset to change the pointer value, e.g. byte_add(1) means adding 1 to the pointer value. We can either take the approach in the current patch and add byte_add() later on if needed, or start with ptr_add() and byte_add() naming. Signed-off-by: Boqun Feng --- rust/kernel/sync/atomic.rs | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs index e62c3cd1d3ca..cbe5d40d9e36 100644 --- a/rust/kernel/sync/atomic.rs +++ b/rust/kernel/sync/atomic.rs @@ -197,3 +197,32 @@ fn from_repr(repr: Self::Repr) -> Self { repr as _ } } + +/// ```rust +/// use kernel::sync::atomic::{Atomic, Relaxed}; +/// +/// let s: &mut [i32] = &mut [1, 3, 2, 4]; +/// +/// let x = Atomic::new(s.as_mut_ptr()); +/// +/// x.add(1, Relaxed); +/// +/// let ptr = x.fetch_add(1, Relaxed); // points to the 2nd element. +/// let ptr2 = x.load(Relaxed); // points to the 3rd element. +/// +/// // SAFETY: `ptr` and `ptr2` are valid pointers to the 2nd and 3rd elements of `s` with writing +/// // provenance, and no other thread is accessing these elements. +/// unsafe { core::ptr::swap(ptr, ptr2); } +/// +/// assert_eq!(s, &mut [1, 2, 3, 4]); +/// ``` +impl generic::AllowAtomicArithmetic for *mut T { + type Delta = isize; + + /// The behavior of arithmetic operations + fn delta_into_repr(d: Self::Delta) -> Self::Repr { + // Since atomic arithmetic operations are wrapping, so a wrapping_mul() here suffices even + // if overflow may happen. + d.wrapping_mul(core::mem::size_of::() as _) as _ + } +}