linux-kernel - Re: [PATCH v3 0/6] Enable strict percpu address space checks

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Message-Id: <20241212193541.fa3dcac867421a971c38135c@linux-foundation.org>
Date: Thu, 12 Dec 2024 19:35:41 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 linux-bcachefs@...r.kernel.org, linux-arch@...r.kernel.org,
 netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Dennis Zhou
 <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter
 <cl@...ux.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Andy
 Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>, Nadav Amit
 <nadav.amit@...il.com>, Brian Gerst <brgerst@...il.com>, Dan Carpenter
 <dan.carpenter@...aro.org>, "H . Peter Anvin" <hpa@...or.com>, Peter
 Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 0/6] Enable strict percpu address space checks

On Sun,  8 Dec 2024 21:45:15 +0100 Uros Bizjak <ubizjak@...il.com> wrote:

> Enable strict percpu address space checks via x86 named address space
> qualifiers. Percpu variables are declared in __seg_gs/__seg_fs named
> AS and kept named AS qualified until they are dereferenced via percpu
> accessor. This approach enables various compiler checks for
> cross-namespace variable assignments.
> 
> Please note that current version of sparse doesn't know anything about
> __typeof_unqual__() operator. Avoid the usage of __typeof_unqual__()
> when sparse checking is active to prevent sparse errors with unknowing
> keyword. The proposed patch by Dan Carpenter to implement
> __typeof_unqual__() handling in sparse is located at:

google("what the hell is typeof_unequal") failed me.

I think it would be nice to include within the changelog (and code
comments!) an explanation-for-others of what this thing is and why
anyone would want to use it.  Rather than assuming that all kernel
developers are typeof() experts!