Re: [PATCH] kexec, remove panic_on_warn kernel parameter from kdump situations

From: Vivek Goyal <vgoyal@redhat.com>
To: Prarit Bhargava <prarit@redhat.com>
Cc: Dave Young <dyoung@redhat.com>,
	kexec@lists.infradead.org, WANG Chao <chaowang@redhat.com>
Subject: Re: [PATCH] kexec, remove panic_on_warn kernel parameter from kdump situations
Date: Fri, 2 Jan 2015 08:17:09 -0500	[thread overview]
Message-ID: <20150102131709.GB18785@redhat.com> (raw)
In-Reply-To: <54A69808.4010401@redhat.com>

On Fri, Jan 02, 2015 at 08:07:20AM -0500, Prarit Bhargava wrote:
> 
> 
> On 01/02/2015 07:54 AM, Vivek Goyal wrote:
> > On Tue, Dec 30, 2014 at 09:57:51AM -0500, Prarit Bhargava wrote:
> >> panic_on_warn kernel parameter will cause the kernel to panic when a
> >> WARN() is hit in the kernel.  This is not a good situation for the kdump
> >> kernel because then it would be possible for the kdump kernel to panic in
> >> a non-fatal WARN().
> >>
> >> This patch removes panic_on_warn as a kernel parameter for the kdump
> >> kernel.
> >>
> > 
> > I think modifying kexec-tools is not best place for this. It probably is better to take care of this in distribution specific scripts.
> > 
> > In the past we have learnt that it is best that kexec-tools does least
> > amount of manipulation with command line.
> 
> Well .. here's the question to think about: what does adding panic_on_warn to
> the kdump kernel get you?  AFAICT, nothing.

Let us consider a hypothetical situation. What if we have some buggy code
which will corrupt file system in certain situation and we detect that
situation and throw a warning. 

In that case as a work around specifying panic_on_warn in kdump kernel
will make sense as we don't want to make further progress if we hit
the warning as it has potential to corrupt fs.

Again this is hypothetical but it can happen. So panic_on_warn might
still be useful in kdump kernel for some corner debugging cases.

That's why I think we should do it in distribution specific scripts
and that too only if user did not specify panic_on_warn for second
kernel explicitly.

> 
> If panic_on_warn is specified, the only thing that will happen is that kdump
> will fail (which is always bad IMO).  There is no real difference in the stack
> trace between the WARN() and panic situations so there is no information loss.
> 
> So I disagree -- we should never specify panic_on_warn on kdump kernel.

I am saying that do it in distribution specific scripts and not in 
kexec-tools.

Thanks
Vivek

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec