Re: [PATCH V4] kernel, add bug_on_warn

From: Jason Baron <jbaron@akamai.com>
To: Prarit Bhargava <prarit@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>, Jonathan Corbet <corbet@lwn.net>,
	kexec@lists.infradead.org, Rusty Russell <rusty@rustcorp.com.au>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	Fabian Frederick <fabf@skynet.be>,
	isimatu.yasuaki@jp.fujitsu.com, "H. Peter Anvin" <hpa@zytor.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-api@vger.kernel.org, vgoyal@redhat.com
Subject: Re: [PATCH V4] kernel, add bug_on_warn
Date: Mon, 27 Oct 2014 14:05:57 -0400	[thread overview]
Message-ID: <544E8985.50203@akamai.com> (raw)
In-Reply-To: <1414155207-29839-1-git-send-email-prarit@redhat.com>

Hi Prarit,

On 10/24/2014 08:53 AM, Prarit Bhargava wrote:
> There have been several times where I have had to rebuild a kernel to
> cause a panic when hitting a WARN() in the code in order to get a crash
> dump from a system.  Sometimes this is easy to do, other times (such as
> in the case of a remote admin) it is not trivial to send new images to the
> user.panic_on_stackoverflow
>
> A much easier method would be a switch to change the WARN() over to a
> BUG().  This makes debugging easier in that I can now test the actual
> image the WARN() was seen on and I do not have to engage in remote
> debugging.
>
> This patch adds a bug_on_warn kernel parameter and
> /proc/sys/kernel/bug_on_warn calls BUG() in the warn_slowpath_common()
> path.  The function will still print out the location of the warning.
>
> An example of the bug_on_warn output:
>
> The first line below is from the WARN_ON() to output the WARN_ON()'s location.
> After that the new BUG() call is displayed.
>
>  WARNING: CPU: 27 PID: 3204 at
> /home/rhel7/redhat/debug/dummy-module/dummy-module.c:25 init_dummy+0x28/0x30
> [dummy_module]()
>  bug_on_warn set, calling BUG()...
>  ------------[ cut here ]------------
>  kernel BUG at kernel/panic.c:434!

Seems reasonable-I'm wondering why you just don't call panic() in this
case. The BUG() call at line '434' doesn't at anything since its just being
called from panic.c.

So something like 'panic_on_warn' would seem to be more appropriate
in keeping with things like 'panic_on_oops' or 'panic_on_stackoverflow'.

Thanks,

-Jason

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