From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AFF602571A7; Mon, 24 Feb 2025 12:07:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740398839; cv=none; b=XCOuBmt4TanssUJ8bf75GghRB8ndbgXtMUnQdZG5nzPfrUByskHud2FYF+/Cu3UGNVRQ1072nb+Ix0T93i+hb/yR7kZVqzxnuV5PzGz4TDl2V5QfTLF1SXi/4Wi1zvO+SvrX/ZoXjS/Yc8HzIZoT4oS67KpZ+teuKyzPOFRBQdg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740398839; c=relaxed/simple; bh=Lj7AnxrvrJdZGqg0jt9Y26sh/3qsXsYiQTfMs9xf2bo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=bhWeit/ywx05mWPZtJmIg7IPwCqkaZUHaqxCQQzBxQa2MtxeEsxwlLLZlBzLKLO5Jb2xeuNjE3H0eOXeEbnY5YRwf0lEDPNR19sXCfDYE4Xl43ky4Y84VsK0lgNFB+Bms9ZoUNNq7DDyoc/mk2F5zsBOWAjlEIVpsXkvlrV5UZ0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=llLJM4oI; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="llLJM4oI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D4B2C4CEE6; Mon, 24 Feb 2025 12:07:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740398839; bh=Lj7AnxrvrJdZGqg0jt9Y26sh/3qsXsYiQTfMs9xf2bo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=llLJM4oIRH1SLrvaPQn/ZipABAJlry7z52TN2eJOr3wP5G9JsfqnpscjFGCMEcK0x 8h6u8Z8F9FO/IrKvQmSInGHVYZyjCA4n8NPAdChcqiW8pamjDLpiYEm/tjc1KD1chO gPgq6fG6Butmyj5gzgDdtMxtB+a8bgmhCk+9RG+Ra7a56X29e0UiAVXPW3RYiNi45m GKySzUVt2gWhsMERCGpGydGPZc8P0Qu9aivv0nTPC6JCU5JbBR2+BquXhVrMNqw5ve 0hpKJoEX3QmwYqoMfcgj+WrvP2XJq43S05I2/+KvqbGPfdboYqVmmDHe5UMv7BGhRo BxtX0sof8DcyA== Date: Mon, 24 Feb 2025 13:07:14 +0100 From: Danilo Krummrich To: Alexandre Courbot Cc: Dave Airlie , Gary Guo , Joel Fernandes , Boqun Feng , John Hubbard , Ben Skeggs , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org Subject: Re: [RFC PATCH 0/3] gpu: nova-core: add basic timer subdevice implementation Message-ID: References: <20250217-nova_timer-v1-0-78c5ace2d987@nvidia.com> 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=us-ascii Content-Disposition: inline In-Reply-To: CC: Gary On Mon, Feb 24, 2025 at 10:40:00AM +0900, Alexandre Courbot wrote: > This inability to sleep while we are accessing registers seems very > constraining to me, if not dangerous. It is pretty common to have > functions intermingle hardware accesses with other operations that might > sleep, and this constraint means that in such cases the caller would > need to perform guard lifetime management manually: > > let bar_guard = bar.try_access()?; > /* do something non-sleeping with bar_guard */ > drop(bar_guard); > > /* do something that might sleep */ > > let bar_guard = bar.try_access()?; > /* do something non-sleeping with bar_guard */ > drop(bar_guard); > > ... > > Failure to drop the guard potentially introduces a race condition, which > will receive no compile-time warning and potentialy not even a runtime > one unless lockdep is enabled. This problem does not exist with the > equivalent C code AFAICT, which makes the Rust version actually more > error-prone and dangerous, the opposite of what we are trying to achieve > with Rust. Or am I missing something? Generally you are right, but you have to see it from a different perspective. What you describe is not an issue that comes from the design of the API, but is a limitation of Rust in the kernel. People are aware of the issue and with klint [1] there are solutions for that in the pipeline, see also [2] and [3]. [1] https://rust-for-linux.com/klint [2] https://github.com/Rust-for-Linux/klint/blob/trunk/doc/atomic_context.md [3] https://www.memorysafety.org/blog/gary-guo-klint-rust-tools/