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

[Vivek Goyal]

On Tue, Jan 06, 2015 at 04:05:00PM +0800, Dave Young wrote:
> On 01/05/15 at 08:54pm, Vivek Goyal wrote:
> > On Tue, Jan 06, 2015 at 09:44:05AM +0800, Dave Young wrote:
> > > On 01/02/15 at 08:17am, 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.
> > > 
> > > Thinking of user who use upstream kexec-tools instead of distribution toolset,
> > > In case kexec --reuse-cmdline, it will copy /proc/cmdline, but user will have
> > > no way to remove part of them.
> > > 
> > > I do want to insist on removing 'panic_on_warn' in upstream kexec-tools, but
> > > we should give user an option to remove it. Something like:
> > > 
> > > kexec --reuse-cmdline --remove-params="panic_on_warn" will be good.
> > 
> > If user is using --reuse-commandline at the same time does not want some
> > of the parameters from command line, then don't use --reuse-commandline.
> > 
> > This is overenginnering. First provide an option to reuse the commandline
> > and provide another option to selectively remove some parameters from that
> > commandline.
> > 
> > What's wrong with existing parameters of --command-line. This just allows
> > user to specify whatever command line is suitable.
> > 
> > So, no, we should not provide --remove-params. If existing command line
> > does not work for new kenrel, then user should not use
> > --reuse-commandline option.
> 
> Hmm, ok. So hope one who is use panic_on_warn in 1st kernel know what he is doing
> and do not simply copy the 1st kernel cmdline for 2nd kernel.

--reuse-commandline will work only for kexec case and not kdump case. And
in case of kexec, it is fine to use panic_on_warn in kexeced kernel. So 
there is no need to worry here.

Thanks
Vivek