linux-kernel - Re: [PATCH] Documentation: coding-style: don't encourage WARN*()

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Date: Mon, 15 Apr 2024 09:26:40 -0700
From: Kees Cook <keescook@...omium.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Christoph Hellwig <hch@...radead.org>, Alex Elder <elder@...aro.org>,
	corbet@....net, workflows@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Documentation: coding-style: don't encourage WARN*()

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