linux-kernel - Re: [PATCH V4] kernel, add bug_on

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Date:	Mon, 27 Oct 2014 14:05:57 -0400
From:	Jason Baron <jbaron@...mai.com>
To:	Prarit Bhargava <prarit@...hat.com>
CC:	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Fabian Frederick <fabf@...net.be>, vgoyal@...hat.com,
	isimatu.yasuaki@...fujitsu.com, linux-doc@...r.kernel.org,
	kexec@...ts.infradead.org, linux-api@...r.kernel.org
Subject: Re: [PATCH V4] kernel, add bug_on_warn

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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