linux-kernel - Re: [PATCH] rust: Test page_align usize::MAX boundary edges

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Message-ID: <aVO6ISXoEV-43AY2@fedora-g16.bne-home.net>
Date: Tue, 30 Dec 2025 21:40:17 +1000
From: Brendan Shephard <bshephar@...-home.net>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: aliceryhl@...gle.com, lorenzo.stoakes@...cle.com,
	Liam.Howlett@...cle.com, ojeda@...nel.org, boqun.feng@...il.com,
	gary@...yguo.net, bjorn3_gh@...tonmail.com, lossin@...nel.org,
	a.hindborg@...nel.org, tmgross@...ch.edu, dakr@...nel.org,
	linux-mm@...ck.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: Test page_align usize::MAX boundary edges

On Tue, Dec 30, 2025 at 11:14:37AM +0100, Miguel Ojeda wrote:
> On Tue, Dec 30, 2025 at 10:55 AM Brendan Shephard <bshephar@...-home.net> wrote:
> >
> > @miguel, Thanks for the pointers in:
> > https://lore.kernel.org/all/CANiq72kcMLXz=xyZeKC0=j_e0BzJEY3wGpBTTxfJsc6EZhCnXA@mail.gmail.com/
> > https://lore.kernel.org/rust-for-linux/CANiq72mLPvB_6Ow3bW5-V4-km=RyA59chQ1g1x9qUt2P-zZweg@mail.gmail.com/
> >
> > Let me know if this addresses the points you were raising in those.
> > Maybe you just wanted usize::MAX and then one over? The first test
> > case might be unnecessary. The last two do a fine job of illustrating the
> > point I think.
> 
> Thanks! Yeah, either way looks good to me. Personally, I tend to like
> tests that check both edges.
> 
> By the way, the original comment mentioned "overflow" explicitly,
> which was good since it conceptually links to the main docs which also
> mention it. It also seemed more aligned with the other two comments.
> Perhaps you changed it since now one of them doesn't return `None`? In
> that case, I would just remove that bit e.g.
> 
>     // Requested address causes overflow.
> 
Yeah ok, I agree. I like the explicit mention of overflow, and you are
indeed correct in your assumption for why I changed it. I'll change it
back to the original comment.

> i.e. I think it is clear that the first case is not the overflow one.
> But it is not a big deal either way.
> 
> By the way, in commit messages, we normally don't use paragraphs like:
> 
>     This patch is a follow-up of: "[PATCH v8] rust: Return Option from
> page_align and ensure no usize overflow"
> 
Ack. I'll remove this. I found a similar commit message in the history,
but it did feel like an awkward way to handle it. Noted for future
reference.
> Instead, it is better to provide a lore.kernel.org permalink to the
> patch or, if the patch was already applied, refer directly to the
> commit with the hash and title. However, in cases like this where it
> is not really important for the change itself, I would just move that
> line below the `---` line so that it is not part of the commit
> message.
> 
> I hope that helps!
> 
> Cheers,
> Miguel

Thanks, I'll send a new revision.