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

From: Simon Horman <horms@verge.net.au>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Prarit Bhargava <prarit@redhat.com>,
	kexec@lists.infradead.org, Dave Young <dyoung@redhat.com>,
	WANG Chao <chaowang@redhat.com>
Subject: Re: [PATCH] kexec, remove panic_on_warn kernel parameter from kdump situations
Date: Mon, 5 Jan 2015 10:49:47 +0900	[thread overview]
Message-ID: <20150105014947.GC10874@verge.net.au> (raw)
In-Reply-To: <20150102131709.GB18785@redhat.com>

On Fri, Jan 02, 2015 at 08:17:09AM -0500, Vivek Goyal wrote:
> 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.

I have reverted this patch until some consensus is reached.

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