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Date: Mon, 15 Apr 2024 09:26:40 -0700
From: Kees Cook <keescook@chromium.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@infradead.org>, Alex Elder <elder@linaro.org>,
	corbet@lwn.net, workflows@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Documentation: coding-style: don't encourage WARN*()
Message-ID: <202404150919.042E6FF@keescook>
References: <20240414170850.148122-1-elder@linaro.org>
 <ZhzgTeEHFF19N3UZ@infradead.org>
 <2024041544-fester-undead-7949@gregkh>
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In-Reply-To: <2024041544-fester-undead-7949@gregkh>

On Mon, Apr 15, 2024 at 10:35:21AM +0200, Greg KH wrote:
> On Mon, Apr 15, 2024 at 01:07:41AM -0700, Christoph Hellwig wrote:
> > No, this advice is wronger than wrong.  If you set panic_on_warn you
> > get to keep the pieces.  
> > 
> 
> But don't add new WARN() calls please, just properly clean up and handle
> the error.  And any WARN() that userspace can trigger ends up triggering
> syzbot reports which also is a major pain, even if you don't have
> panic_on_warn enabled.

Here's what was more recently written on WARN:

https://docs.kernel.org/process/deprecated.html#bug-and-bug-on

Specifically:

- never use BUG*()
- WARN*() should only be used for "expected to be unreachable" situations

This, then, maps correctly to panic_on_warn: System owners may have set
the panic_on_warn sysctl, to make sure their systems do not continue
running in the face of "unreachable" conditions.

As in, userspace should _never_ be able to reach a WARN(). If it can,
either the logic leading to it needs to be fixed, or the WARN() needs to
be changed to a pr_warn().

-- 
Kees Cook