[PATCHv2 2/2] [fs] proc/vmcore: check the dummy place holder for offline cpu to avoid warning

[Liu ping fan]

On Wed, Dec 21, 2016 at 11:57 AM, Pratyush Anand <panand at redhat.com> wrote:
>
>
> On Wednesday 21 December 2016 08:56 AM, Xunlei Pang wrote:
>>
>> On 12/20/2016 at 11:38 PM, Pratyush Anand wrote:
>>>
>>>
>>>
>>> On Monday 19 December 2016 08:10 AM, Dave Young wrote:
>>>>
>>>> Hi, Pingfan
>>>>
>>>> On 12/19/16 at 10:08am, Pingfan Liu wrote:
>>>>>>
>>>>>> kexec-tools always allocates program headers for present cpus. But
>>>>>> when crashing, offline cpus have dummy headers. We do not copy these
>>>>>> dummy notes into ELF file, also have no need of warning on them.
>>>>
>>>> I still think it is not worth such a fix, if you feel a lot of warnings
>>>> in case large cpu numbers, I think you can change the pr_warn to
>>>> pr_warn_once, we do not care the null cpu notes if it has nothing bad
>>>> to the vmcore.
>>>>
>>>
>>> I agree. Warning is more like information here. May be, we can count the
>>> number of times real_sz was 0, and then can print an info at the end in
>>> stead of warning, like..."N number of CPUs would have been offline, PT_NOTE
>>> entries was absent for them."
>>
>>
>> Well, OTOH the warning may also be due to some user-space misuse, we can't
>> distinguish that without extra information added.
>
>
> Yes, yes..I agree, I meant that the above info is just indicative. May be
> "might have been" could be better word than "would have been" in the above
> info print message.
>
>
>>
>> Another possible user-space fix would be: Firstly fix kexec-tools to add
>> notes only for online cpus,
>> then utilize udev rules(cpu online/offline events) to automatically
>> trigger kdump kernel reload.
>
>
> Hummm..this is certainly possible. But can we do much even when we get the
> info that the PT_NOTE was compromised by user space?
>
If doing this, kexec should be re-forked each time when
online/offline. I think it is not worth to do so just for suppressing
some warning.

> Therefore, I am of the view that if at all we are concerned about number of
> warning messages in case of multiple offline cpu, then we can just print the
> total number of NULL PT_NOTE at the end of loop.
>
Yes, I think it is a good idea. NULL PT_NOTES are only caused by
offlne cpu, it is better to change the waring to info

Thx,
Pingfan