linux-kernel - Re: [PATCH 3/4] gpu: nova-core: gsp: fix improper handling of empty slot in cmdq

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Message-Id: <DFV0F28KHNXP.3JU1QGBJCZBUQ@nvidia.com>
Date: Thu, 22 Jan 2026 18:27:45 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Eliot Courtney" <ecourtney@...dia.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "John Hubbard" <jhubbard@...dia.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Alistair Popple"
 <apopple@...dia.com>, <nouveau@...ts.freedesktop.org>,
 <rust-for-linux@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>, "dri-devel"
 <dri-devel-bounces@...ts.freedesktop.org>
Subject: Re: [PATCH 3/4] gpu: nova-core: gsp: fix improper handling of empty
 slot in cmdq

On Thu Jan 22, 2026 at 2:07 PM JST, Eliot Courtney wrote:
> On Thu Jan 22, 2026 at 12:26 PM JST, John Hubbard wrote:
>> On 1/21/26 6:59 PM, Eliot Courtney wrote:
>>> +            // The area is contiguous and we leave an empty slot before `rx`.
>>> +            // PANIC: since `rx > tx` we have `rx - tx - 1 >= 0`
>>> +            // PANIC: since `tx < rx < MSGQ_NUM_PAGES && after_tx.len() == MSGQ_NUM_PAGES - tx`:
>>> +            //   `rx - 1 <= MSGQ_NUM_PAGES` -> `rx - tx - 1 <= MSGQ_NUM_PAGES - tx`
>>> +            //   -> `rx - tx - 1 <= after_tx.len()`
>>
>> Hi Eliot,
>>
>> Documentation nit: the proofs are great, but the above just does
>> not go into my head easily, because it's a proof, rather than a
>> sentence.
> I had a look now and I agree that it looks like plain English is the
> defacto standard for the PANIC comments, so I will update them.
>
> But, I wonder what people think about this. IMO it makes sense to have
> SAFETY and PANIC comments as rigorous proofs (where practical and
> possible) to match the level of work the compiler does for us in the
> infalliable areas of the code - if an issue occurs, unsafe or panicking
> code is often the root cause IMO. Writing these in plain English is
> easier to read but also harder to verify that the proof is correct and
> harder to verify if there are any implicit assumptions.
>
> I see there are some guidelines about SAFETY: comments but not about
> PANIC: comments in Documentation/rust/coding-guidelines.rst.

Would be interesting to have Miguel/Alice and the core team's opinion
on this IMHO.