linux-kernel - Re: [PATCH 00/11] x86: WARN() hackery

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Message-ID: <20250703-spotted-panther-of-blizzard-a887ad@houat>
Date: Thu, 3 Jul 2025 15:40:01 +0200
From: Maxime Ripard <mripard@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kees@...nel.org, 
	acarmina@...hat.com, jpoimboe@...nel.org, mark.rutland@....com, 
	torvalds@...uxfoundation.org
Subject: Re: [PATCH 00/11] x86: WARN() hackery

Hi,

On Sat, Jun 07, 2025 at 11:42:24AM +0200, Peter Zijlstra wrote:
> Slightly less mad this time :-)
> 
> The primary purpose of all this is to get the WARN() printk() and
> __warn() calls into the same context. Notably the current state is that
> WARN() ends up doing printk() in-place, then takes an exception and has
> the exception do the __warn().
> 
> The problem with all this is the ONCE logic. Normal WARN_ON_ONCE()
> (without the printk) has the ONCE logic in the exception
> (__report_bug()). But because WARN() essentially results in two distinct
> actions (printk + trap) this cannot work.  With the result that
> additional ONCE logic is sprinkled around for each such site.
> 
> Current proposals look to make this worse by adding KUnit checks for all
> this, including regular WARN. Making the per-instance code overhead even
> worse.
> 
> As such, by moving the printk() into the exception, and having the
> exception (__report_bug() in fact) do everything, we get rid of the
> external ONCE logic and provide a cental place for additional conditions
> without need to litter all the instances.

Thanks a lot for working on that. What is the status of this patch? It
looks like Linus was happy with it, and I understood that you felt it
was a blocker for the kunit warning work we'd really like to get merged
at some point.

Thanks again,
Maxime

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