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[103.168.172.201]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4a9949fb04asm65446731cf.20.2025.07.07.08.13.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Jul 2025 08:13:27 -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 8712BF40068; Mon, 7 Jul 2025 11:13:26 -0400 (EDT) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Mon, 07 Jul 2025 11:13:26 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdefgdefvddufecutefuodetggdotefrod ftvfcurfhrohhfihhlvgemucfhrghsthforghilhdpuffrtefokffrpgfnqfghnecuuegr ihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjug hrpeffhffvvefukfhfgggtugfgjgesthekredttddtjeenucfhrhhomhepuehoqhhunhcu hfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrdgtohhmqeenucggtffrrghtth gvrhhnpeejhfeikeekffejgeegueevffdtgeefudetleegjeelvdffteeihfelfeehvdeg keenucffohhmrghinhepkhgvrhhnvghlrdhorhhgnecuvehluhhsthgvrhfuihiivgeptd enucfrrghrrghmpehmrghilhhfrhhomhepsghoqhhunhdomhgvshhmthhprghuthhhphgv rhhsohhnrghlihhthidqieelvdeghedtieegqddujeejkeehheehvddqsghoqhhunhdrfh gvnhhgpeepghhmrghilhdrtghomhesfhhigihmvgdrnhgrmhgvpdhnsggprhgtphhtthho pedviedpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtoheprghlihgtvghrhihhlhesgh hoohhglhgvrdgtohhmpdhrtghpthhtoheprgdrhhhinhgusghorhhgsehkvghrnhgvlhdr ohhrghdprhgtphhtthhopehojhgvuggrsehkvghrnhgvlhdrohhrghdprhgtphhtthhope grlhgvgidrghgrhihnohhrsehgmhgrihhlrdgtohhmpdhrtghpthhtohepghgrrhihsehg rghrhihguhhordhnvghtpdhrtghpthhtohepsghjohhrnhefpghghhesphhrohhtohhnmh grihhlrdgtohhmpdhrtghpthhtohepmhgrshgrhhhirhhohieskhgvrhhnvghlrdhorhhg pdhrtghpthhtohepnhgrthhhrghnsehkvghrnhgvlhdrohhrghdprhgtphhtthhopehmtg hgrhhofheskhgvrhhnvghlrdhorhhg X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Mon, 7 Jul 2025 11:13:25 -0400 (EDT) Date: Mon, 7 Jul 2025 08:13:25 -0700 From: Boqun Feng To: Alice Ryhl Cc: Andreas Hindborg , Miguel Ojeda , Alex Gaynor , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Masahiro Yamada , Nathan Chancellor , Luis Chamberlain , Danilo Krummrich , Benno Lossin , Nicolas Schier , Trevor Gross , Adam Bratschi-Kaye , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, Petr Pavlu , Sami Tolvanen , Daniel Gomez , Simona Vetter , Greg KH , Fiona Behrens , Daniel Almeida , linux-modules@vger.kernel.org Subject: Re: [PATCH v15 1/7] rust: sync: add `SetOnce` Message-ID: References: <20250707-module-params-v3-v15-0-c1f4269a57b9@kernel.org> <20250707-module-params-v3-v15-1-c1f4269a57b9@kernel.org> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org 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 Mon, Jul 07, 2025 at 03:38:58PM +0200, Alice Ryhl wrote: > On Mon, Jul 7, 2025 at 3:32 PM Andreas Hindborg wrote: > > > > Introduce the `SetOnce` type, a container that can only be written once. > > The container uses an internal atomic to synchronize writes to the internal > > value. > > > > Signed-off-by: Andreas Hindborg > > LGTM: > Reviewed-by: Alice Ryhl > > > +impl Drop for SetOnce { > > + fn drop(&mut self) { > > + if self.init.load(Acquire) == 2 { > > + // SAFETY: By the type invariants of `Self`, `self.init == 2` means that `self.value` > > + // contains a valid value. We have exclusive access, as we hold a `mut` reference to > > + // `self`. > > + unsafe { drop_in_place(self.value.get()) }; > > This load does not need to be Acquire. It can be a Relaxed load or > even an unsynchronized one since the access is exclusive. Right, I think we can do the similar as Revocable here: if *self.init.get_mut() == 2 { } Further, with my following Benno's suggestion and making `Atomic` an `UnsafeCell: https://lore.kernel.org/rust-for-linux/aGhh-TvNOWhkt0JG@Mac.home/ compiler can generate a noalias reference here, which allows further optimization. Regards, Boqun > > Alice