Re: [PATCH 0/2] add new notifier function ,take2

[Takenori Nagano <t-nagano@ah.jp.nec.com>]

Vivek Goyal wrote:
> On Thu, Oct 18, 2007 at 12:06:51AM -0700, Andrew Morton wrote:
>> On Thu, 18 Oct 2007 15:45:08 +0900 Takenori Nagano <t-nagano@ah.jp.nec.com> wrote:
>> I can sort-of see what this is doing.  Runtime-definable management of
>> which notifier functions will be called on a panic?  Or maybe I
>> misunderstood.
>>
>> But even if I did understand, I don't understand why Linux needs this
>> feature - what are the use cases, what is the value to our users?
>>
>> Can you please flesh that information out a bit more?
>>
>
> Hi Andrew,
> 
> Takenori wants to make kdb and kdump co-exist. Currently after panic()
> panic_notifier_list is not executed if kdump is configured. Before list
> is executed, system will boot into second kernel to capture the dump. Hence
> if even if kdb was registered on panic_notifier_list, it will never get
> a chance to run.

Yes, it is true. But I don't mind only kdb and kdump co-exist.

Keith Owen said,

> > My stance is that _all_ the RAS tools (kdb, kgdb, nlkd, netdump, lkcd,
> > crash, kdump etc.) should be using a common interface that safely puts
> > the entire system in a stopped state and saves the state of each cpu.
> > Then each tool can do what it likes, instead of every RAS tool doing
> > its own thing and they all conflict with each other, which is why this
> > thread started.
> > 
> > It is not the kernel's job to decide which RAS tool runs first, second
> > etc., it is the user's decision to set that policy. Different sites
> > will want different orders, some will say "go straight to kdump", other
> > sites will want to invoke a debugger first. Sites must be able to
> > define that policy, but we hard code the policy into the kernel. 

I agreed with him and I made new notifier function that users can change
the order. Priority value in notifier blocks are hardcoded. If users want to
change list order, they have to rebuild kernel. I think it is very unhappy.

This is our discussion.
http://www.gossamer-threads.com/lists/linux/kernel/797220?do=post_view_threaded#797220

In addition, we can use new notifier function to reboot_notifier, die_chain
if users want to use.

>> The patches are somewhat wordwrapped - please check your email client
>> configuration, thanks.

Sorry, I'll resend.

Thanks,
  Takenori