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 A02E61ABEC5; Sun, 27 Apr 2025 10:13:16 +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=1745748798; cv=none; b=bFOK8Q2vkFcXYPKZXRlqdn6HucFUpPRF+C24MDdyb2C3m0TZrxUPIvPzLeNNWy1D2tBCNlN55VjypoWzRnIrLAEiRZPqoG+gmiz8ffqm2nUcIuMz1j2Y4Uw9CtxfpbeEJbKd1PxNLvehLlkM6FZY10r0gguC+qVqch0mHcqqAak= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745748798; c=relaxed/simple; bh=yegWmCWPr2oBxNhpO1pLh+k+JNbNoD8FKo7GQBRmCuA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mxJ22+zNYkDW6isSR2dNs2H7c4SWyG00GFGvBHMI2AjyPStFVAOuxHTM+XXnYSmnvgow8k5CunuFyNcXR4b+ExlAPWcZbq0/9oX09hsnG0+7aCBa1Gwx10JpiYGoQYiucrU/gOtxogDuqOKvnjZXMnPNxFkzzW5Cn9pn+Dk2bo8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=udUSNP0I; 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="udUSNP0I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 905FEC4CEE3; Sun, 27 Apr 2025 10:13:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745748796; bh=yegWmCWPr2oBxNhpO1pLh+k+JNbNoD8FKo7GQBRmCuA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=udUSNP0IT8mcewRV2I8tuq9DP95xYgTlZ7nt+etgUFssGHTIMXDnKCRuAjv6sxKbq MkFWDdM1bWjKLAYoqeqDqxnDw4NJXs3rVA0iFw1YRewHpCYmO7RwPci+IDD2nCr/vj cI++n+TrL7q7SKO5vTKyconTFptAEzbVto57W2cwBLDD9y+dNr0QLgjvR6cHT6EXxS 264GbpV6Xwk1W4QinDdw5kweYwCRClDl677vTXzRL+6CIXk2dOHtc0O+TjUxB0CcRN OuAaayF1Zrtw1TdS2B3YjBJXlXf8jUZ1f+L7U92+KULcGWSHioEKU/2X8Q+UPODJbl gwwCBC5hs6rxA== Date: Sun, 27 Apr 2025 12:13:08 +0200 From: Danilo Krummrich To: Benno Lossin Cc: gregkh@linuxfoundation.org, rafael@kernel.org, bhelgaas@google.com, kwilczynski@kernel.org, zhiw@nvidia.com, cjia@nvidia.com, jhubbard@nvidia.com, bskeggs@nvidia.com, acurrid@nvidia.com, joelagnelf@nvidia.com, ttabi@nvidia.com, acourbot@nvidia.com, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, linux-pci@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] rust: revocable: implement Revocable::access() Message-ID: References: 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 Sun, Apr 27, 2025 at 08:37:00AM +0000, Benno Lossin wrote: > On Sat Apr 26, 2025 at 11:18 PM CEST, Danilo Krummrich wrote: > > On Sat, Apr 26, 2025 at 08:24:14PM +0000, Benno Lossin wrote: > >> On Sat Apr 26, 2025 at 3:30 PM CEST, Danilo Krummrich wrote: > >> > Implement an unsafe direct accessor for the data stored within the > >> > Revocable. > >> > > >> > This is useful for cases where we can proof that the data stored within > >> > the Revocable is not and cannot be revoked for the duration of the > >> > lifetime of the returned reference. > >> > > >> > Signed-off-by: Danilo Krummrich > >> > --- > >> > The explicit lifetimes in access() probably don't serve a practical > >> > purpose, but I found them to be useful for documentation purposes. > >> > --- > >> > rust/kernel/revocable.rs | 12 ++++++++++++ > >> > 1 file changed, 12 insertions(+) > >> > > >> > diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs > >> > index 971d0dc38d83..33535de141ce 100644 > >> > --- a/rust/kernel/revocable.rs > >> > +++ b/rust/kernel/revocable.rs > >> > @@ -139,6 +139,18 @@ pub fn try_access_with R>(&self, f: F) -> Option { > >> > self.try_access().map(|t| f(&*t)) > >> > } > >> > > >> > + /// Directly access the revocable wrapped object. > >> > + /// > >> > + /// # Safety > >> > + /// > >> > + /// The caller must ensure this [`Revocable`] instance hasn't been revoked and won't be revoked > >> > + /// for the duration of `'a`. > >> > >> Ah I missed this in my other email, in case you want to directly refer > >> to the lifetime, you should keep it defined. I would still remove the > >> `'s` lifetime though. > >> > + pub unsafe fn access<'a, 's: 'a>(&'s self) -> &'a T { > >> > + // SAFETY: By the safety requirement of this function it is guaranteed that > >> > + // `self.data.get()` is a valid pointer to an instance of `T`. > >> > >> I don't see how the "not-being revoked" state makes the `data` ptr be > >> valid. Is that an invariant of `Revocable`? (it's not documented to have > >> any invariants) > > > > What else makes it valid? > > IMO an `# Invariants` section with the corresponding invariant that > `data` is valid when `is_available` is true. Yeah, I agree that the # Invariants section is indeed missing and should be fixed. > > AFAICS, try_access() and try_access_with_guard() argue the exact same way, > > except that the reason for not being revoked is the atomic check and the RCU > > read lock. > > Just because other code is doing the same mistake doesn't make it > correct. If I had reviewed the patch at that time I'm sure I would have > pointed this out. I would say that try_access() and try_access_with_guard() are wrong, they rely on the correct thing, we just missed documenting the corresponding invariant. > I opened an issue about this: > > https://github.com/Rust-for-Linux/linux/issues/1160 Thanks for creating the issue! What do you suggest for this patch?