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 3F764142E67; Sun, 27 Apr 2025 17:28:37 +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=1745774918; cv=none; b=TZ3Znw+4Ijbf2n9pnzay2nAIgnUrJNNtZb59GgcNz7LQ/Sjxt7INC8eSUAxKPhN/piAFZTBpqHSM5mkwru/Rzp4BlYi2eP1Y/CDTFRVseh9WDFDZQ95JVaxfs1vLjCQdZkEDbFkghKBqUW6AL7imfzJ+lXEL58gZTYNDth5tV6s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745774918; c=relaxed/simple; bh=JrwaRlQRSbsnDWUu8IbBHR4MU4nqMGZK9i4gOpXUCBo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AsROD9wA/II3HKTx2diW7VvQejnkPOyjY1JQYd9QYQv8R5VlGkuXeO9i5Nn1Nb3B9QKd3TWdqmZi4wf1jbCB6SjRneXB2KfgxUeS3fgF7lcAxpaxoZo2HaWDYHQScgvt0hoE9VKQHysFXGVaf8I+NKzFg0TAHK0KtmmXTMS3624= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sWezRnjw; 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="sWezRnjw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1347FC4CEE3; Sun, 27 Apr 2025 17:28:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745774917; bh=JrwaRlQRSbsnDWUu8IbBHR4MU4nqMGZK9i4gOpXUCBo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sWezRnjwEwe4W/vTCGZD6EzWc+ng2GZn1SNhcVfbRX2Gt3mGeemTBxqbMV7SEv6V+ /qP0OJqTyfuy6UP75avtZVw0bGQz7Z1rY91rXj+yAMl1gByUeX4hpaq3/vrBJMxsZW xKwoaFbyhfWqbKxi/6jglVtDoCGRGNpK6vEkycx95vN/+QqMrYI18iyTBAkx7X7q0x 5cY09FA5OjJdck/Way8CiGV76uPDPniHJnwizzQCWQzFfwIAIFycN0jmscNJwgqQOK npf+1TzgDJeX5ozl/tP2GTWbF/bfLSFrSerTrKUXwAYEI/ovTBX5ksEw5x66A8oKpn r8DXZIQLcPYBQ== Date: Sun, 27 Apr 2025 19:28:30 +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 05:15:48PM +0000, Benno Lossin wrote: > On Sun Apr 27, 2025 at 12:13 PM CEST, Danilo Krummrich wrote: > > 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 > > Did you mean to write `wouldn't`? Otherwise the second part doesn't > match IMO. Yes, I meant "wouldn't". :) > > > on the correct thing, we just missed documenting the corresponding invariant. > > Yeah it's not a behavior error, but since you agree that something > should be fixed, there also is something that is 'wrong' :) > > >> 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? > > I don't mind if you take it with the lifetime changes, so > > Reviewed-by: Benno Lossin > > But I'd like the invariant to be documented (maybe we should tag the > issue with good-first-issue -- I don't actually think it is one, but > maybe you disagree). Yes, it should be documented; regarding the issue you created, I'd be fine marking it as good-first-issue. But I'd also be fine sending a fix for this myself outside the scope of this series.