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 6F6FC194A44; Mon, 24 Feb 2025 12:11:23 +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=1740399083; cv=none; b=HABZ98tqXMaAqh59+yw7jI9GrHClt6ZzqJWLJDKs6tVDX5h70siZi1smXgQKQjL0/SyRWnzXFuSX9OsSmR5yjbVp+/2/EAQXYFUddxizD1Zqw1gupFqabMbSEHBoMSjZ9TUex/XIm9s9vUBrWygHYxAi+LEhuGlaa5qm7LCrDaY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740399083; c=relaxed/simple; bh=ji86S+6hkK6jvEu8J3uKVH9gFMsbNKK9qSj8rPf2IYo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pNRJv5wJhK6wjaG40kQ3V125mY5SN8YZpTSjoCGabC3D9QuvDAqicXQskchIF3xNP9+LCxqH1GVOpxbIGeVq6Mmqb6Yq04PztoQQshco4Z1Wuz21gAu6Q2e7BQDdoNRfvFwSeow8XGvZ/xb4ZsBFKHUFoAFDUZS2K/tGCJ6o1zE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WjLUBFT+; 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="WjLUBFT+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E8EAC4CED6; Mon, 24 Feb 2025 12:11:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740399083; bh=ji86S+6hkK6jvEu8J3uKVH9gFMsbNKK9qSj8rPf2IYo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WjLUBFT+aQe/w0i30iEK0+Bl/rX6PURlwNIcc12p7APTHAvuAc2UMi+I5qBs2tKGn 4l7p/pxNtSEZpc0qflUFl0Z/Xk2tMeCF42QFAdEru26eHTkPmsTRMHrD1vCs5IZOcJ 8JZXbQETu+0OKu+BkgchYQCFhch7XKPOBvkWYRB78S5RFIW+Rx+yWn4Vh/Cl8usQRI z0R2MlmtaBrGDOOVxWTIjC0mOKnV0iyXgrrm3xiw9NipF9NoQJq08nERJeefr+jg5f XrxpHk1fyYqIP+oiziXTePlI0FAdiu5b+/b3fgxrcQqIe7lUy32DA3QDPHJxttskdc zEPYIgddcwS3w== Date: Mon, 24 Feb 2025 13:11:17 +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: On Mon, Feb 24, 2025 at 01:07:19PM +0100, Danilo Krummrich wrote: > 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 Without klint [1] it is exactly the same as in C, where I have to remember to not call into something that might sleep from atomic context. > > 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/